Diets in Oncology

THE UNDERLYING IDEA

In animal models, short-term starvation protected healthy cells from chemotherapy toxicity while increasing its effect on cancer cells ^[1]. Two variants have been tested in humans: true fasting (several dozen hours on water only, around chemotherapy administration) and the fasting-mimicking diet, a several-day menu very low in calories and protein, designed to make the body respond as it would to a fast ^[1][2].

WHAT THE LARGEST RANDOMISED TRIAL SHOWED

The DIRECT trial (phase 2, 131 patients with HER2-negative stage II/III breast cancer) compared a fasting-mimicking diet used for 3 days before and during neoadjuvant chemotherapy with a regular diet ^[1]. Results:

• no difference in toxicity between the groups, despite dexamethasone being omitted in the fasting arm ^[1];
• a radiologically complete or partial response occurred more often in the diet group (OR 3.168; p=0.039) ^[1];
• in the per-protocol analysis, a Miller-Payne 4/5 pathological response, meaning 90-100% tumour-cell loss, was more likely (OR 4.109; p=0.016) ^[1];
• the diet reduced chemotherapy-induced DNA damage in T-lymphocytes ^[1].

WHY THIS IS STILL NOT ENOUGH

The key pathological-response result comes from a per-protocol analysis rather than from all randomised patients, meaning it counted only those who actually kept to the diet ^[1]. Such an analysis inherently favours the tested method, because patients able to tolerate several days of food restriction are usually in better general condition. An independent 2025 systematic review covering 9 studies and 354 patients concluded plainly that fasting is safe and feasible, but that no effect on treatment outcomes or chemotherapy-related toxicity has been demonstrated ^[2]. The only consistent finding was a fall in insulin and IGF-1, a change in a biological marker rather than in the patient's health ^[2]. The authors explicitly call for large randomised trials before fasting is regarded as an adjunct to therapy ^[2].

WHAT THESE STUDIES DID NOT COVER

DIRECT excluded people with diabetes and those with a BMI below 18 ^[1]. The available studies were dominated by breast cancer patients (258 of 354), generally in good condition and not losing weight ^[2]. This means the data say nothing about fasting in people who are malnourished, losing weight, in cancer cachexia, or with gastrointestinal cancers - and these are precisely the groups most likely to consider restricting food after reading reports about fasting. Absence of data is not the same as evidence of safety.

WHAT THIS MEANS FOR THE READER

Fasting and fasting-mimicking diets remain an investigational approach, not part of standard cancer treatment ^[2]. Maintaining body weight and protein intake during chemotherapy is supported by strong evidence (see the entries on nutritional support and on cachexia), whereas deliberate food restriction is not. Any change to nutrition during cancer treatment is a decision to be made together with the treating team.

Sources

1. de Groot S, et al. — Fasting mimicking diet as an adjunct to neoadjuvant chemotherapy for breast cancer in the multicentre randomized phase 2 DIRECT trial, Nature Communications 2020: europepmc.org ↗
2. Maes J, et al. — Impact of intermittent fasting on patients with cancer undergoing chemotherapy and/or targeted therapies: a systematic review of the literature, Supportive Care in Cancer 2025: europepmc.org ↗

WHAT THIS DIET IS AND WHERE IT CAME FROM. The low-bacterial diet grew out of simple reasoning: if a patient after high-dose chemotherapy has very few granulocytes, cut off the bacteria that come with food. For decades it was standard practice on haematology and transplant wards. Typical restrictions include:

• raw vegetables and fruit, especially those that cannot be peeled,
• mould-ripened and soft ripened cheeses, unpasteurised products,
• raw or undercooked meat, fish and eggs,
• loose nuts, sprouts, unpasteurised honey.

WHAT THE EVIDENCE SHOWS

A 2025 systematic review covered 5 randomised trials and a total of 510 adults after high-dose therapy and haematopoietic stem cell transplantation; none of the analysed endpoints - infections, gastrointestinal complications, mortality, length of hospital stay - favoured the neutropenic diet ^[1].

A second 2025 systematic review, published together with a clinical practice guideline, pooled 8 randomised trials in children with cancer and haematopoietic cell transplant recipients. The data were consistent: food restrictions lack clinically significant benefit in preventing infections, and the panel issued a conditional recommendation AGAINST their use ^[2].

A single randomised trial in paediatric oncology illustrates this best: among 150 participants, infection during neutropenia occurred in 33% of those following food safety guidelines alone and in 35% of those additionally following the neutropenic diet - no statistically significant difference, while the restrictive arm reported a clearly greater adherence burden ^[5].

An earlier 2019 meta-analysis reached the same conclusion in adults: no statistically significant difference in major infections or in bacteraemia and fungaemia between the neutropenic and the regular diet, with a slightly HIGHER infection risk on the restrictive diet in the stem cell transplant subgroup. The authors conclude that there is no evidence to support the use of a neutropenic diet or other food restrictions in neutropenic patients with cancer, and refer instead to food-handling guidelines ^[4].

A 2023 systematic review (12 reports, 3,469 participants) adds the quality-of-life dimension: the low-bacterial diet did not reduce infection or mortality rates compared with a free diet, and was associated with poorer quality of life resulting from a limited and less palatable menu ^[6].

STRENGTH OF EVIDENCE

Moderate and consistent in direction. In its favour: the data come from randomised trials rather than observations, and several independent systematic reviews converge on the same conclusion ^[1][2][4][6]. Against full certainty: the individual trials are small, the definition of the low-bacterial diet varies between centres, and the paediatric guideline recommendation is CONDITIONAL rather than strong ^[2]. The honest summary is therefore: no benefit has been demonstrated - not "the diet has been proven harmful".

DOES LIBERALISING THE DIET HELP BY ITSELF

The honest answer is: on its own, not much. In a randomised trial in patients undergoing haematopoietic stem cell transplantation, a liberalised diet encouraging fresh fruit and vegetables did not improve energy intake during neutropenia (678 versus 724 kcal per day; p=0.46) or protein intake ^[3]. Lifting the restrictions is therefore not by itself a remedy for malnutrition - planned nutritional support is what is needed.

WHAT THESE RESULTS DO NOT SAY

They do not say that food hygiene no longer matters. Safe food-handling rules - thorough washing, avoiding raw meat, fish and eggs, respecting use-by dates, separate boards and utensils for raw produce, avoiding food of uncertain origin - remain recommended regardless of whether a list of banned products is used ^[4][7]. The difference concerns restrictive lists, not hygiene itself.

WHO THIS MATTERS FOR

Primarily patients with haematological malignancies treated with high-dose chemotherapy and stem cell transplantation, because that is the population studied ^[1][2]. For patients with solid tumours who become neutropenic after standard chemotherapy, evidence of this quality does not exist - which does not mean the neutropenic diet helps them, only that it has not been tested in them.

WHAT TO DISCUSS WITH THE TREATING TEAM

Centre practice varies and some units still apply restrictions. The scope of the diet during neutropenia is set by the treating team, which knows the patient's nutritional status and the ward's epidemiological situation.

WHY THIS ENTRY EXISTS AT ALL

Alcohol is rarely treated as a nutritional factor with oncological significance, yet it is one of the best documented. The International Agency for Research on Cancer (IARC) classifies it as a Group 1 carcinogen — the highest category, which also contains asbestos, ionising radiation and tobacco ^[2].

FOR WHICH CANCERS THE LINK IS CAUSAL

The NCI lists cancers of the oral cavity and throat, larynx, oesophagus (squamous cell form), liver, colorectum and breast ^[1]. Risk figures relative to non-drinkers, as given by the NCI ^[1]:

• oral cavity and throat: 1.1 times in light drinkers, 5 times in heavy drinkers;
• oesophagus (squamous cell): 1.3 times in light drinkers, 5 times in heavy drinkers;
• liver: 2 times in heavy drinkers;
• breast: 1.04 times in light, 1.23 times in moderate, 1.6 times in heavy drinkers;
• colorectum: 1.2 to 1.5 times in moderate to heavy drinkers.

IS THERE A SAFE DOSE

WHO answers plainly that there is not: "there is no safe amount that does not affect health", and the risk "starts from the first drop" ^[3]. This is not rhetoric — WHO states that half of alcohol-attributable cancers in the European Region arise from light and moderate consumption (less than 1.5 litres of wine, 3.5 litres of beer or 450 ml of spirits weekly), and that this very pattern accounts for the majority of alcohol-attributable breast cancers in women ^[3].

HOW ALCOHOL DAMAGES CELLS

The NCI points to several parallel mechanisms ^[1]: conversion of ethanol to acetaldehyde, a carcinogen that damages DNA; generation of reactive oxygen species and oxidative damage; impaired absorption of nutrients; increased absorption of other carcinogens (which explains the overlap between alcohol and tobacco); raised oestrogen levels; disrupted folate metabolism.

WHAT STOPPING ACHIEVES

The NCI states that discontinuing alcohol reduces the risk of cancers of the mouth, throat, oesophagus, breast and colorectum, while noting that "it may take years for the risks of cancer to return to those of never drinkers" — and adding that it is never too late to stop ^[1].

WHAT THESE DATA DO NOT SAY

They do not say that, in someone already under cancer treatment, stopping alcohol replaces any part of that treatment; the figures quoted concern the RISK OF DEVELOPING cancer, not the treatment of diagnosed disease. Nor do they establish how large the effect is in an individual — these are population-level risks, overlaid by tobacco use, family history and other factors. Decisions about management of cancer are made by the specialist physician.

Sources

1. National Cancer Institute — Alcohol and Cancer Risk (Fact Sheet): cancer.gov ↗
2. IARC Monographs on the Identification of Carcinogenic Hazards to Humans — Alcohol consumption, Group 1 (via WHO/Europe): who.int ↗
3. World Health Organization, Regional Office for Europe — No level of alcohol consumption is safe for our health (2023): who.int ↗

WHAT EXACTLY IARC ASSESSED

In October 2015 a working group of the International Agency for Research on Cancer assessed two separate things ^[1]:

• PROCESSED MEAT — meat transformed through salting, curing, fermentation, smoking or other processes to enhance flavour or preservation (sausages, ham, cured and canned meats, dried meat): GROUP 1, the category of agents carcinogenic to humans. The basis was SUFFICIENT EVIDENCE from epidemiological studies that eating it causes colorectal cancer ^[1];
• RED MEAT — unprocessed mammalian muscle meat (beef, veal, pork, lamb, mutton, horse, goat): GROUP 2A, probably carcinogenic to humans. Here the epidemiological evidence was LIMITED — positive associations with colorectal cancer were seen, but other explanations could not be ruled out; strong mechanistic evidence tipped the assessment ^[1].

WHAT "GROUP 1" DOES NOT MEAN. Group 1 speaks to the STRENGTH OF EVIDENCE that something causes cancer, not to the SIZE OF THE RISK. Tobacco smoke sits in the same group, but — as IARC itself stresses — this does not make a slice of ham as dangerous as a cigarette ^[1]. The classification answers "does it cause cancer", not "by how much".

SO BY HOW MUCH DOES RISK RISE

WHO gives one concrete figure: each 50 g portion of processed meat eaten daily increases the risk of colorectal cancer by about 18% ^[1]. This is a RELATIVE risk — an increase measured from a person's baseline risk, not 18 extra cases per hundred people. For red meat no comparable firm figure was given, because the evidence is limited ^[1].

IS THERE A SAFE PORTION

WHO states that the available data DID NOT PERMIT a conclusion on whether a risk-free level of consumption exists ^[1]. That is neither confirmation nor denial of a safety threshold — it is an honest statement of the limit of current knowledge.

WHAT FOLLOWS IN PRACTICE

WHO does not issue its own dietary recommendations here — it notes that national governments and health agencies do — but recalls its 2002 position: people who eat meat should moderate their consumption of processed meat in order to reduce the risk of colorectal cancer ^[1]. WHO also notes that red meat has nutritional value (protein, iron, zinc, vitamin B12), so weighing risks against benefits is a matter for national health authorities ^[1].

WHAT THIS ENTRY DOES NOT SAY

It does not say how any individual should eat — whether healthy or ill. The figures quoted concern the RISK OF DEVELOPING cancer in a population, not the treatment of diagnosed disease or diet during therapy. Nor does it say that avoiding meat guarantees freedom from colorectal cancer: risk also reflects family history, age, obesity, physical activity, tobacco and alcohol. Decisions about nutrition during cancer are made by the treating physician together with a clinical dietitian.

Sources

1. World Health Organization — Q&A: Cancer, carcinogenicity of the consumption of red meat and processed meat (IARC Monographs Volume 114): who.int ↗

WHERE THE MYTH COMES FROM

Many tumours take up glucose faster than surrounding tissue (the phenomenon described as the Warburg effect), and PET imaging with labelled glucose is built on exactly this. From that true observation a conclusion is often drawn that does not follow: if the tumour feeds on sugar, then cutting out sugar should starve it. The body, however, keeps blood glucose within a narrow range regardless of what is on the plate - it also produces glucose from other nutrients. Diet does not cut off the tumour's supply.

WHAT THE REFERENCE SOURCE SAYS

The National Cancer Institute answers the question of whether sugar makes cancer worse directly: research has shown that cancer cells consume more glucose than normal cells, but NO study has shown that eating sugar makes cancer worse, or that stopping sugar makes a tumour shrink or disappear ^[1]. The same material notes at the same time that a high-sugar diet may contribute to weight gain, and greater body weight is associated with increased cancer risk ^[1].

THE INDIRECT ROUTE - BODY WEIGHT

• sugar-sweetened drinks: the World Cancer Research Fund grades the evidence that they cause weight gain, overweight and obesity as strong, and describes the mechanism explicitly as indirect - no separate carcinogenic mechanism of the drink itself has been identified ^[2];
• excess body weight in adults: convincing-grade evidence for increased risk of cancers of the oesophagus (adenocarcinoma), pancreas, liver, colorectum, breast (postmenopausal), kidney and endometrium ^[3];
• the prevention conclusion: limiting sugar-sweetened drinks is well justified, but as a tool of weight control, not as a direct anticancer action.

WHAT THIS MEANS FOR A PATIENT ON TREATMENT

This is where the myth can do harm. Patients during chemotherapy, radiotherapy and after gastrointestinal surgery often have reduced appetite, altered taste and difficulty meeting their energy requirements. Introducing a diet at that moment that eliminates simple sugars, and often other carbohydrates too, removes from the menu the foods that are easiest to eat and most energy-dense. Weight loss and malnutrition in cancer are a documented problem with consequences of their own - they worsen tolerance of treatment. No study shows that a benefit from cutting sugar outweighs that risk.

WHAT THIS ENTRY DOES NOT SAY

We are not claiming that sugar is harmless - an excess of simple sugars promotes weight gain, dental caries and type 2 diabetes, and those are reasons to limit it. Nor are we assessing the ketogenic diet as a treatment; that has its own entry in this catalogue. We claim only this much: manipulating the amount of sugar in the diet is not a documented way of treating cancer or slowing its growth.

THE DECISION BELONGS TO THE DOCTOR

Nutrition during cancer treatment, and especially any elimination diet, is decided by the treating team together with a clinical dietitian. This entry describes the state of knowledge, not a recommendation for an individual.

Sources

1. [1] National Cancer Institute — Common Cancer Myths and Misconceptions (sekcja: Does sugar make cancer worse?): cancer.gov ↗
2. [2] World Cancer Research Fund — Limit sugar sweetened drinks: evidence for our recommendations (mocne dowody na przyrost masy ciała, mechanizm opisany jako pośredni): wcrf.org ↗
3. [3] World Cancer Research Fund — Be a healthy weight: evidence for our recommendations (dowody przekonujące dla siedmiu nowotworów): wcrf.org ↗

STRENGTH OF THE EVIDENCE

In the World Cancer Research Fund classification only a few dietary factors reach the top grade. Fibre and wholegrains are among them: the expert panel grades as strong the evidence that wholegrains DECREASE the risk of colorectal cancer, and that foods containing dietary fibre decrease that risk and protect against weight gain ^[1]. In the previous edition of the report the evidence for fibre was graded probable - after review of new data it was upgraded ^[1].

NUMBERS FROM THE META-ANALYSIS

• 25 prospective studies, dose-response analysis ^[2];
• per 10 g of total dietary fibre per day: relative risk 0.90 (95% CI 0.86-0.94), 16 studies ^[2];
• per three servings of wholegrains per day (about 90 g): relative risk 0.83 (95% CI 0.78-0.89), 6 studies ^[2];
• in practice this is a graded relationship: the benefit grows with intake, with no clear threshold at which it begins.

WHERE THE EFFECT MAY COME FROM

WCRF names two main mechanisms. Fibre is fermented by colonic microflora into short-chain fatty acids, including butyrate, which in experimental studies inhibits proliferation of colon cancer cells. The second mechanism is mechanical: fibre shortens intestinal transit time and increases faecal bulk, so potential faecal mutagens have less time in contact with the mucosa ^[1].

TRANSLATING THIS INTO A DIET

• the WCRF recommendation: at least 30 g of fibre a day and at least 400 g of a variety of non-starchy vegetables and fruit a day ^[1];
• sources are wholegrain bread and pasta, groats (buckwheat, barley, oat), brown rice, pulses, vegetables and fruit;
• the recommendation speaks explicitly of fibre FROM FOOD - not of fibre supplements, for which no such cancer-risk data exist;
• the same dietary factor works in a second direction: fibre-rich food protects against weight gain, and excess body weight is a separate, documented risk factor for many cancers ^[1].

WHAT THESE DATA DO NOT SAY

All the cited results come from observational studies of prevention: they concern the risk of DEVELOPING cancer in healthy people. They are not evidence that increasing fibre intake after a cancer diagnosis affects the course of the disease, recurrence or survival. People who eat a lot of fibre also differ from others in other health behaviours, and despite statistical adjustment that influence cannot be fully separated out.

WHEN FIBRE MAY BE CONTRAINDICATED

This is the most important caveat for a reader who is ill rather than healthy. A high-residue diet is not right for everyone: with narrowing or threatened obstruction of the gastrointestinal tract, in the perioperative period after bowel surgery, with a stoma in the early period after formation, during and after pelvic radiotherapy complicated by enteritis, and in severe diarrhoea after treatment - in these situations a diet with the OPPOSITE profile, low-residue, is often advised. This is decided by the treating team together with a clinical dietitian, not by a general prevention recommendation.

Sources

1. [1] World Cancer Research Fund — Eat a diet rich in wholegrains, vegetables, fruit and beans: evidence for our recommendations (mocne dowody dla raka jelita grubego, cel 30 g błonnika dziennie): wcrf.org ↗
2. [2] Aune D i wsp. — Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies, BMJ 2011 (25 badań prospektywnych, PMID 22074852): europepmc.org ↗
3. [3] World Cancer Research Fund — Diet, nutrition, physical activity and colorectal cancer (raport przeglądowy Continuous Update Project): wcrf.org ↗

WHAT EXACTLY IS PROVEN

WCRF frames it as strong evidence that certain high-salt foods are a cause of stomach cancer, and names them: foods preserved by salting, such as meat and fish, and salt-preserved vegetables ^[1]. The more of these foods a person eats, the greater their chance of developing the disease ^[1].

WHAT IS NOT PROVEN - THE MOST COMMONLY CONFUSED PART: The evidence on total dietary salt intake is weaker. WCRF states plainly that studies covering populations worldwide did NOT show a strong link between total salt intake and stomach cancer ^[1]. A statement about the salt cellar and a statement about salted and fermented preserves are not the same statement and do not carry the same evidential weight.

WHERE THESE DATA COME FROM

The main studies were conducted in Asia, above all in Japan and Korea, because in those culinary traditions many foods are preserved by salting and fermentation rather than by refrigeration as in most Western countries ^[1]. This matters directly for a reader in Poland: the intakes observed in those studies are far higher than is typical of a Central European diet, so transferring the result to a Polish menu is an approximation rather than direct data.

PROPOSED MECHANISM

Salt damages the stomach lining and causes lesions which, if left to develop, can become stomach cancer ^[1]. A second strand concerns Helicobacter pylori infection - its effect is made worse in the presence of salt ^[1]. H. pylori infection is a separate, well-documented risk factor for stomach cancer and is the principal factor in this diagnosis, not diet.

A SEPARATE ITEM - CANTONESE-STYLE SALTED FISH

The International Agency for Research on Cancer (IARC) found sufficient evidence that Chinese-style salted fish causes cancer of the nasopharynx, and sufficient evidence linking it with stomach cancer ^[2]. This is a distinct product category singled out by IARC, not a general statement about fish.

WHAT FOLLOWS IN PRACTICE

• WCRF made no global recommendation on salt-preserved foods, because these products are eaten mainly in Asia; the expert panel nevertheless advises that it is best not to consume them ^[1];
• on salt itself, WCRF points to the World Health Organization threshold: below 5 g of salt a day ^[1]. This is a public health recommendation, framed mainly around blood pressure, not an oncological recommendation for an individual;
• preserving food by refrigeration instead of salting is the element that changed the risk picture in Western countries.

WHAT THIS ENTRY DOES NOT SAY

All the evidence cited concerns PREVENTION - the risk of developing cancer in healthy people. It is not data on the effect of reducing salt on the course of a diagnosed cancer, on recurrence or on survival. In patients undergoing cancer treatment the diet is often modified for entirely different reasons (loss of appetite, altered taste, risk of malnutrition, coexisting heart and kidney disease), and those modifications are decided by the treating team together with a clinical dietitian, not by a general prevention recommendation.

Sources

1. [1] World Cancer Research Fund — Salt: shaking up the link with stomach cancer (mocne dowody dla żywności konserwowanej solą; brak silnego związku dla całkowitego spożycia soli; próg WHO 5 g dziennie): wcrf.org ↗
2. [2] World Cancer Research Fund — Limit red and processed meat: evidence for our recommendations (stanowisko IARC: solona ryba w stylu chińskim a rak nosogardła i rak żołądka): wcrf.org ↗

TWO RESULTS THAT DO NOT ADD UP TO ONE RECOMMENDATION:

• colorectal cancer: WCRF grades as strong the evidence that dairy products DECREASE the risk, and separately that taking calcium supplements decreases it too ^[1];
• prostate cancer: there is evidence that higher consumption of dairy products MAY INCREASE the risk of this cancer, and that diets high in calcium may increase it ^[1]; this evidence is weaker than that for colorectal cancer and is stated in conditional terms;
• the consequence for recommendations: WCRF did not include dairy among its Cancer Prevention Recommendations precisely because the balance differs between cancers ^[1].

WHY THIS MATTERS RATHER THAN MERELY BEING INTERESTING

A reader looking for a single answer to whether dairy is good or bad will not find one - not because science has yet to catch up, but because the answer depends on which cancer is meant. The institution that has been collecting these data for decades concluded that the most honest course was to issue no recommendation. Publications that present dairy unambiguously, either as protective or as a threat, omit half of the evidence.

PROPOSED MECHANISM

The protective effect of dairy against colorectal cancer is linked above all to its calcium content ^[1]. That same component, however, is suspected of contributing to the second, opposite signal concerning the prostate ^[1]. These are not two independent strands but one component assessed in two different organs.

ON CALCIUM SUPPLEMENTS

WCRF extends the strong evidence of reduced colorectal cancer risk to calcium supplements as well ^[1]. We give no doses or dosing schedule here: that would be advice for an individual rather than a description of the state of knowledge, and with calcium the decision has to take account of factors outside oncology (kidney stones, kidney disease, concurrent medication). Separately we repeat the general rule: the treating physician should be told about all supplements being taken.

WHAT THIS ENTRY DOES NOT SAY

All the evidence cited concerns PREVENTION - the risk of developing cancer in healthy people. It is not data on the effect of dairy intake on the course of a diagnosed cancer, on recurrence or on survival. Nor does it address situations in which dairy is restricted for entirely different reasons: lactose intolerance, diarrhoea after treatment, disturbances of calcium and phosphate balance. In cancer, on the other hand, dairy can be an important source of energy and protein for people at risk of malnutrition - and in practice that consideration decides more often than the epidemiology of risk.

THE DECISION BELONGS TO THE DOCTOR

Nutrition and supplementation during cancer treatment are decided by the treating team together with a clinical dietitian. This page describes the state of knowledge and is not advice for any individual.

Sources

1. [1] World Cancer Research Fund — Dairy and cancer (mocne dowody na zmniejszenie ryzyka raka jelita grubego przez produkty mleczne i suplementy wapnia; dowody na możliwe zwiększenie ryzyka raka gruczołu krokowego; powód braku zalecenia): wcrf.org ↗
2. [2] World Cancer Research Fund — Be a healthy weight: evidence for our recommendations (kontekst: zalecenia profilaktyczne WCRF i kategorie siły dowodów): wcrf.org ↗

WHY THIS IS A TOPIC AT ALL

A supplement suggests risk; a fruit does not. A patient who honestly lists every preparation they take will usually not mention the daily glass of grapefruit juice. Yet this is one of the best-documented food-drug interactions in all of pharmacology, and in oncology it concerns drugs taken by mouth, daily, for many months.

MECHANISM: The furanocoumarins present in grapefruit inhibit the cytochrome P450 enzyme CYP3A4 ^[1]. CYP3A4 metabolises a great many anticancer drugs, so inhibiting it changes how much drug reaches the bloodstream. The key point is that this change happens OUTSIDE dosing control: the patient takes the prescribed dose, while the body behaves as if it had received a different one.

WHAT HAS BEEN MEASURED — THE NUMBERS:

• NILOTINIB: in a clinical trial, combination with grapefruit juice increased the area under the concentration curve by 29% and peak serum concentration by 60% ^[1];
• SUNITINIB: a clinical trial observed increased bioavailability after grapefruit juice exposure ^[1];
• IMATINIB: a clinical review indicates the juice may raise plasma levels by inhibiting CYP3A4 and trigger organ toxicity ^[1];
• ETOPOSIDE: the OPPOSITE direction — after grapefruit juice pretreatment, bioavailability fell from about 73% to 52%, corresponding to a 26% reduction in area under the curve ^[1].

WHY THE DIRECTION CAN REVERSE

This is the most commonly misunderstood part. The popular belief is that grapefruit makes drugs stronger. With etoposide the opposite occurred, and that situation is the more dangerous one, because lower exposure to an anticancer drug means weaker treatment than planned and produces no symptom by which it could be noticed. Toxicity is visible; loss of efficacy is not.

NOT ONLY GRAPEFRUIT

Alongside grapefruit, NCI names fruits with comparable interaction potential: Seville orange (an ingredient of marmalades and some liqueurs), pomelo and lime ^[1].

WHAT THIS ENTRY DOES NOT SAY

It neither recommends nor discourages eating grapefruit for any individual and gives no safe quantities — NCI publishes interaction tables but makes no explicit recommendation about avoiding grapefruit during cancer therapy ^[1], and the answer depends on the specific drug a patient is taking. Most intravenous chemotherapy is unaffected; the issue concerns chiefly oral drugs metabolised by CYP3A4.

WHAT TO TELL THE TREATING TEAM

About regular consumption of grapefruit juice or these fruits — ideally before oral treatment begins. The question to ask the doctor or clinical pharmacist is simply: is my drug metabolised by CYP3A4. That single question settles the matter, and the answer is in the summary of product characteristics.

Sources

1. [1] National Cancer Institute — Cancer Therapy Interactions With Foods and Dietary Supplements (PDQ), Health Professional Version (furanokumaryny i CYP3A4; nilotynib AUC +29% i Cmax +60%; sunitynib; imatynib; etopozyd 73% do 52%, AUC -26%; pomarancza sewilska, pomelo, limonka): cancer.gov ↗

WHY THIS ENTRY SITS IN THE DIET CATALOGUE

Body weight is not an ingredient of a menu, but in the WCRF classification it is a factor with stronger evidence behind it than most individual foods. Put differently: HOW MUCH a person eats, and how it is stored, weighs more in the risk calculation than WHAT exactly they eat. That is why this entry stands beside the ones on fibre or processed meat, not instead of them.

WHICH CANCERS THIS CONCERNS

WCRF names thirteen diagnoses for which the link with overweight and obesity is established ^[1]:

• bowel cancer,
• post-menopausal breast cancer,
• gallbladder cancer,
• kidney cancer,
• liver cancer,
• cancers of the mouth, pharynx and larynx,
• oesophageal adenocarcinoma,
• ovarian cancer,
• pancreatic cancer,
• advanced prostate cancer,
• stomach (cardia) cancer,
• womb cancer.

Important distinctions in this list: for breast it is the POST-menopausal period, for oesophagus it is adenocarcinoma (not squamous cell carcinoma), for stomach it is the cardia (not the whole organ), and for prostate it is advanced disease. These qualifications are part of the evidence, and dropping them changes the meaning of the sentence.

PROPOSED MECHANISM

WCRF describes it briefly and cautiously: having too much body fat can cause inflammation and increase the levels of certain hormones in the body, and these factors can increase the risk of cancer cells developing ^[1]. This explains why the list covers hormone-dependent cancers (post-menopausal breast, womb) alongside gastrointestinal ones.

WHAT THE RECOMMENDATION SAYS

WCRF puts it in one sentence: as part of our Cancer Prevention Recommendations, we recommend that people be a healthy weight ^[1]. This is a PUBLIC HEALTH recommendation addressed to a population, not advice for an individual.

WHAT THIS ENTRY DOES NOT SAY — THE PART THAT MATTERS MOST TO A READER WHO IS ILL:

• it does not say that losing weight treats cancer. The data concern the risk of DEVELOPING cancer in healthy people, not the course of a diagnosed disease;
• it does not say that a person with a diagnosis should reduce their weight. During cancer treatment the situation is often the OPPOSITE: malnutrition and unintentional weight loss worsen treatment tolerance and are a separate clinical problem, covered on this site in the entries on nutritional support and cancer cachexia;
• unintentional weight loss is not an achievement but a symptom to report to a doctor;
• it contains no thresholds, no weight-loss diets and no target values for any individual. Those are decided by the physician together with a clinical dietitian who know the patient's nutritional status and comorbidities.

AN HONEST CAVEAT ON THE STRENGTH OF EVIDENCE

These are observational data from population studies. They show a reproducible and strong association, but people of differing body weight also differ in other health behaviours, and part of that influence cannot be fully separated out despite statistical adjustment. WCRF grades this evidence as strong, which denotes consistency of results and a plausible mechanism, not a randomised experiment.

Sources

1. [1] World Cancer Research Fund — Obesity, weight gain and cancer risk (lista trzynastu nowotworow zwiazanych z nadmierna iloscia tkanki tluszczowej; mechanizm zapalny i hormonalny; zalecenie utrzymania prawidlowej masy ciala): wcrf.org ↗

WHAT IARC CONCLUDED

In 2016 an IARC Working Group reviewed more than 1000 observational and experimental studies covering over 20 cancer sites and found the evidence for the carcinogenicity of coffee drinking INADEQUATE. Coffee was moved from Group 2B (possibly carcinogenic), where it had sat since 1991, to Group 3 — not classifiable ^[1]. IARC notes that the earlier classification was a valid reading of the data available in 1991; the change reflects accumulated evidence, not a past error.

WHAT THE WCRF GRADING SAYS

The World Cancer Research Fund and the American Institute for Cancer Research grade the evidence that coffee DECREASES risk as probable for two cancers: hepatocellular carcinoma and cancer of the uterine corpus (endometrium) ^[2]. In the WCRF scheme, "probable" is the second strongest grade, after "convincing". For endometrial cancer the association was seen for both caffeinated and decaffeinated coffee, which argues against attributing it to caffeine alone ^[2].

WHERE THE REAL RISK LIES — TEMPERATURE, NOT THE DRINK. The same IARC evaluation classified drinking VERY HOT beverages in Group 2A (probably carcinogenic to humans) in relation to squamous cell carcinoma of the oesophagus; this concerns beverages consumed at around 65°C and above ^[1]. IARC points out that in most countries coffee and tea are not drunk at such temperatures — the habit is common in parts of South America, Central Asia and East Africa. The practical content of this evaluation therefore differs from the headline "hot drinks cause cancer": what was assessed is temperature, not coffee, tea or mate.

WHAT THESE GRADINGS DO NOT SAY

An IARC classification describes the STRENGTH OF EVIDENCE for carcinogenicity, not the size of the risk — Group 2A does not mean an agent is as hazardous as every other agent in that group. The WCRF grading, in turn, describes associations observed across populations; it does not support the conclusion that drinking coffee will protect a given person from liver cancer, or that someone who does not drink coffee should start. Neither grading concerns the TREATMENT of cancer.

WHAT THIS MEANS FOR A PATIENT IN TREATMENT

The data above concern the risk of developing cancer in the general population, not management during therapy. Caffeine can interact with some medicines and affect sleep, hydration and gastrointestinal symptoms, and dietary advice during chemotherapy, radiotherapy and after surgery is set individually. Decisions about diet during cancer treatment are made by the treating physician together with the care team.

SOURCES:

• ^[1] IARC Monographs Volume 116: Drinking Coffee, Mate, and Very Hot Beverages (2016/2018) — IARC news release and materials.
• ^[2] World Cancer Research Fund / American Institute for Cancer Research, Continuous Update Project — coffee and liver cancer, coffee and endometrial cancer.

WHY PEOPLE TURN TO IT

The alkaline diet and alkaline water are promoted by the media and by sellers as a way to "de-acidify the body" and thereby hinder cancer growth. The premise is that because cancer cells grow less well in an alkaline environment, the pH of the whole body can be shifted by what a person eats and drinks.

WHAT PHYSIOLOGY SAYS

A systematic review published in BMJ Open documented that dietary changes can alter URINE pH but do not change BLOOD pH. Dietary interventions moved urine pH by 0.2–1.2 units, while blood pH changed by only 0.01–0.02 units, because the kidneys excrete acid effectively and maintain systemic pH balance ^[1]. The premise on which the whole idea rests therefore fails at the level of physiology.

WHAT THE EVIDENCE SAYS

The same review identified 8278 citations and reviewed 252 abstracts. Exactly ONE study met the inclusion criteria ^[1].

• No randomised trials were located.
• No study was found that examined alkaline diet or alkaline water for cancer TREATMENT.
• The single included study found no association between dietary acid load and bladder cancer (OR 1.15; 95% CI 0.86–1.55; p = 0.36) ^[1].

WHAT THIS MEANS FOR THE READER

The authors write that despite promotion of the alkaline diet and alkaline water by the media and salespeople, there is almost no actual research to either support or disprove these ideas, and promoting them for cancer prevention or treatment is not justified ^[1]. "No high-quality evidence" is a complete and honest answer here — neither a promise nor silence replaces it.

It is also worth noting what is at stake beyond the water itself: restrictive versions of the alkaline diet limit protein and grain foods, and weight loss and malnutrition during cancer treatment are documented clinical problems ^[2]. Whether and how to modify eating during cancer is decided by the treating physician together with a clinical dietitian.

Sources

1. [1] Fenton TR, Huang T. Systematic review of the association between dietary acid load, alkaline water and cancer. BMJ Open 2016;6:e010438: pmc.ncbi.nlm.nih.gov ↗
2. [2] NCI PDQ — Nutrition in Cancer Care (Health Professional Version): cancer.gov ↗

WHY IT IS USED

Radioiodine (I-131) is taken up by thyroid cells in exactly the same way as dietary iodine - the two forms compete for the same transport mechanism. The reasoning behind the diet is therefore simple: lowering the pool of non-radioactive iodine before administration should direct more of the dose to where it is meant to act. The diet does not treat the cancer; it is a preparation for treatment and applies only for a defined period before the isotope is given, not permanently.

WHAT IS USUALLY AVOIDED

Restrictions concern mainly the richest dietary sources of iodine:

• iodised salt and processed foods salted with it,
• sea fish, seafood and seaweed (nori, wakame, kombu),
• milk and dairy products, and egg yolks,
• the food colouring E127 (erythrosine) and iodine-containing supplements,
• iodine-containing medicines and iodinated contrast agents - the latter matter far more than food.

WHAT THE EVIDENCE SHOWS

A 2010 systematic review covered 8 studies in which the diet lasted from 4 days to 4 weeks. It reduced urinary iodine excretion in all of them and was associated with increased radioiodine uptake in three. The authors noted, however, that not a single study assessed recurrence or mortality, and cautiously supported the practice of a 1-2 week diet before I-131 administration ^[1].

A 2022 systematic review with meta-analysis (59 reports) framed this more critically. Patients with iodine deficiency (urinary iodine below 50 µg/L) had a higher chance of successful ablation than those with iodine excess (at least 250 µg/L): odds ratio 2.63 (95% CI 1.18-5.86; n=283). By contrast, comparing a STRICTER with a less strict diet showed no meaningful difference: odds ratio 0.67 (95% CI 0.26-1.73; n=256). The certainty of both results was rated as very low ^[2].

The 2022 consensus statement of the European Thyroid Association puts it plainly: a low-iodine diet "may be prescribed but its utility is not demonstrated unequivocally", while any iodine-containing drug must be avoided. The document describes the practice of some centres - restriction to no more than 50 µg of iodine per day for 1-2 weeks - noting that evidence on the effect on ablation success is conflicting ^[3].

STRENGTH OF EVIDENCE

Limited. What is well documented concerns surrogate measures: urinary iodine concentration and isotope uptake ^[1][2]. What matters most to the patient - whether the diet increases the chance of cure and lowers the risk of recurrence - was not examined in any study included in the 2010 review ^[1], and the 2022 meta-analysis rates the certainty of the available results as very low ^[2]. This does not mean the diet is useless; it means that a strong recommendation about how strict or how long it should be has no basis in current data.

THE COST TO THE PATIENT - PART OF THE RESULT, NOT A FOOTNOTE. The 2022 review also covered qualitative studies and described the diet's effect on wellbeing: patients called it boring, confusing and overwhelming, and reported anxiety, uncertainty about permitted foods and self-blame over possible lapses - at an already stressful time ^[2]. Because the demonstrated benefit concerns surrogate measures while the cost is real and felt, tightening restrictions "just in case" is not a neutral choice.

WHAT THESE RESULTS DO NOT UNDERMINE

They do not undermine the need to avoid iodinated contrast agents and iodine-containing medicines before radioiodine treatment - these deliver iodine on a completely different scale from a meal, and the European statement lists avoiding them as an unconditional requirement ^[3].

WHAT TO DISCUSS WITH THE TREATING TEAM

The scope and duration of the diet, when to start it and how to proceed after contrast-enhanced imaging are decided by the treating team - practice differs between centres and also depends on how much iodine the national diet contains. Diagnostic and therapeutic decisions are made solely by a specialist physician.

WHY THIS ENTRY STANDS ON ITS OWN

Most nutrition content in oncology concerns maintaining weight and preventing malnutrition. In sellar region tumours the problem can be the reverse, and transferring the general principle of "eat more so you do not lose weight" here is not merely inapt but potentially harmful.

WHAT THE SOURCE SAYS

• in craniopharyngioma, obesity may occur that can be life-threatening, together with metabolic syndrome including non-alcoholic fatty liver disease ^[1];
• obesity develops in children after both complete and subtotal resection, which the source says suggests that a predilection to obesity is a component of the disease itself rather than solely a consequence of direct hypothalamic injury ^[1];
• posterior hypothalamic involvement by the tumour, or operative injury to it, appeared to be a key factor in the development of severe obesity ^[1];
• separately described are hormone deficiencies — growth hormone, thyroid and cortisol — and the almost universal need for lifelong replacement of multiple pituitary hormones ^[1].

WHY THIS IS NOT ORDINARY OBESITY

The hypothalamus regulates satiety and energy expenditure. When this region is involved by tumour or damaged during treatment, the satiety signal and metabolic rate cease to track the amount of food eaten. The result is weight gain that cannot be explained by eating pattern — which is why attributing it to "lack of discipline" is both unjust and clinically misleading.

A SECOND LAYER - HORMONES

Hypothyroidism and growth hormone deficiency in themselves alter body composition and energy expenditure, and cortisol deficiency is a state of danger. Assessment of body weight after treatment of a tumour in this region therefore cannot be separated from endocrine assessment; that is a task for an endocrinologist, not a question of choosing a diet.

WHAT THIS ENTRY DOES NOT SAY

We give no diet, no calorie figure and no plan of action. We know of no high-quality evidence that any particular pattern of eating reverses hypothalamic obesity; the cited source does not supply it, and we do not substitute conjecture. The general NCI recommendation for survivors of childhood cancer is stated broadly: healthy dietary practices — a diet rich in plant foods and moderate in animal foods — and an active lifestyle, to reduce treatment-related metabolic and cardiovascular complications ^[2].

THE DECISION BELONGS TO THE DOCTOR

Nutritional management and hormone replacement after surgery for a sellar region tumour are decided by the treating team — neurosurgeon, endocrinologist and clinical dietitian. This page describes the state of knowledge and is not advice for any individual.

Sources

1. [1] National Cancer Institute — Childhood Craniopharyngioma Treatment (PDQ), Health Professional Version (otyłość zagrażająca życiu i zespół metaboliczny z NAFLD; otyłość po resekcji doszczętnej i niedoszczętnej jako możliwa składowa samej choroby; zajęcie/uszkodzenie tylnego podwzgórza jako kluczowy czynnik ciężkiej otyłości; niedobory GH, tarczycy i kortyzolu; dożywotnie uzupełnianie hormonów przysadki): cancer.gov ↗
2. [2] National Cancer Institute — Late Effects of Treatment for Childhood Cancer (PDQ), Health Professional Version (ogólne zalecenie: dieta bogata w produkty roślinne i umiarkowana w produkty zwierzęce oraz aktywny tryb życia w celu zmniejszenia metabolicznych i sercowo-naczyniowych następstw leczenia): cancer.gov ↗

WHY THIS LOCATION IN PARTICULAR

NCI states explicitly that nutrition complications are usually most notable and severe with tumors involving the digestive tract or head and neck, owing to mechanical obstruction or dysfunction ^[1]. For this location NCI lists dysphagia and odynophagia, xerostomia and taste changes as typical consequences, and for radiotherapy of the head and neck region — xerostomia, mucositis and taste changes, with thick saliva as a later effect ^[1].

THE SCALE OF THE PROBLEM

A systematic review published in 2026, covering 31 studies, reports that malnutrition affects 30–50% of patients at diagnosis and up to 90% during therapy ^[2]. This is why nutritional status is treated here as part of the treatment plan rather than a side issue: malnutrition directly affects whether the planned radiotherapy or chemoradiotherapy can be delivered without interruption.

WHAT THE EVIDENCE SAYS ABOUT EACH FORM OF SUPPORT. The same review compares three approaches ^[2]:

• oral nutritional supplements — early use was associated with fewer treatment interruptions, particularly before escalation to enteral feeding;
• prophylactic percutaneous endoscopic gastrostomy — associated with reduced weight loss, fewer unplanned hospitalisations and higher treatment completion rates, although the authors explicitly caution that these findings must be interpreted carefully because the available evidence is observational;
• nasogastric tube feeding — associated with fewer device-related complications and lower long-term dependence, but heterogeneity across studies and the predominance of gastrostomy-focused evidence prevented direct comparison.

WHAT THE EVIDENCE DOES NOT SETTLE

The review authors put it plainly: comparative evidence remains insufficient to define the optimal enteral approach, and mucositis, dysphagia and impaired oral intake remained the most significant outcomes DESPITE the implementation of multiple nutritional support measures ^[2]. In other words, nutritional support mitigates the consequences of treatment but does not remove them, and the choice between gastrostomy and nasogastric tube has no randomised-trial answer today. High-quality randomised trials integrating oral health-related outcomes are needed ^[2].

STRENGTH OF EVIDENCE

Moderate. In favour: the data come from a systematic review conducted in accordance with PRISMA, with methodological quality appraisal of the included studies, and the malnutrition figures are consistent and high ^[2]. Against full certainty: the key observations on the benefit of prophylactic gastrostomy come from observational studies rather than randomisation, and are described as such by the authors ^[2].

WHAT THIS ENTRY DOES NOT SAY

It does not indicate which method of feeding any individual patient should choose, or when a gastrostomy should be placed. That decision is made by the treating team — radiation oncologist, head and neck surgeon, clinical dietitian and speech and language therapist — on the basis of nutritional status, the radiotherapy plan and symptom severity. The service does not interpret individual clinical situations.

Sources

1. [1] National Cancer Institute — PDQ: Nutrition in Cancer Care (Health Professional Version): cancer.gov ↗
2. [2] Nutritional management and oral health-related outcomes in head and neck cancer treated with radiotherapy or chemoradiotherapy: a systematic review, BMC Oral Health 2026 (PMID 42010533): pubmed.ncbi.nlm.nih.gov ↗

WHAT ORAL NUTRITIONAL SUPPLEMENTS ARE

They are ready-made liquid or powdered products registered as foods for special medical purposes. In a small volume they provide concentrated energy, protein, fat and carbohydrate, and often fibre, vitamins and minerals. NCI stresses that they are not intended to serve as the sole source of nutrition — they supplement what the patient eats ^[1].

WHAT THE EVIDENCE SHOWS

The strength of evidence is moderate and concerns nutritional indicators rather than survival.

• Multinutrient, high-protein supplements significantly improved total energy and protein intake and reduced the incidence of complications ^[1].
• In head and neck cancer treated with radiotherapy or chemoradiotherapy, early use of supplements was associated with fewer treatment interruptions, particularly before escalation to tube feeding; the review authors note that comparative data remain too limited to define the optimal approach ^[2].
• In perioperative care (a review of patients undergoing prostate cancer surgery), supplements form part of the recommended pathway alongside early screening for malnutrition ^[3].
• A review of 38 studies found NO benefit from fish-oil-enriched supplements in the treatment of cachexia in advanced cancer ^[1].

WHAT SUPPLEMENTS DO NOT SOLVE

A supplement will not by itself halt progressive cancer cachexia, nor replace treatment of the cause of appetite loss. It is not an anticancer drug and there are no data showing an effect on the outcome of cancer treatment.

A PRACTICAL LIMITATION PATIENTS THEMSELVES RAISE

A review of patient experiences after colorectal surgery found that experiences with oral nutritional supplements vary widely, and that palatability largely determines whether they are consumed ^[4]. This is not a minor detail: a supplement that is not drunk does not nourish, and unacceptable taste is a common reason for abandoning advice.

WHERE TO SEEK HELP

Choosing a supplement (energy density, protein content, form, fibre content, suitability in diabetes or renal impairment) is the responsibility of the treating physician and a clinical dietitian. This site does not give dietary advice and does not recommend specific products.

Sources

1. [1] National Cancer Institute — Nutrition in Cancer Care (PDQ), Health Professional Version (oral nutrition supplements; multinutrient high-protein products; systematic review of 38 studies on fish oil in cachexia): cancer.gov ↗
2. [2] Nutritional management and oral health-related outcomes in head and neck cancer treated with radiotherapy or chemoradiotherapy: a systematic review. BMC Oral Health 2026 (PMC13267656): europepmc.org ↗
3. [3] Evidence-based perioperative nutritional management for patients undergoing prostate cancer surgery: a systematic review. Gland Surgery 2026 (PMC13264766): europepmc.org ↗
4. [4] Patient Experiences of Nutrition in Enhanced Recovery After Colorectal Surgery: A Systematic Review. Nutrients 2026 (PMC13258613): europepmc.org ↗

WHY THIS LOCATION IN PARTICULAR

NCI states explicitly that nutrition complications are usually most notable and severe with tumors involving the digestive tract or head and neck, owing to mechanical obstruction or dysfunction ^[1]. For the oesophagus and stomach NCI lists dysphagia and odynophagia as typical consequences, and describes tumour-induced weight loss as occurring frequently in solid tumours of the lung, pancreas and upper gastrointestinal tract, and less often in breast cancer or lower gastrointestinal cancer ^[1]. Surgery adds a further mechanism: NCI notes that procedures including oesophagectomy and gastrectomy may produce early satiety, a premature feeling of fullness ^[1].

THE SCALE OF THE PROBLEM AFTER CHEMORADIOTHERAPY

A secondary analysis of a prospective cohort of 260 patients with oesophageal squamous cell carcinoma treated with concurrent chemoradiotherapy between 2008 and 2024 found that cachexia developed after treatment in 60.7% of patients ^[2]. Independent predictors of cachexia were greater tumour length and a larger tumour-occupying proportion of the lumen, with cut-offs of at least 6 cm in length and at least 70% of the luminal area ^[2].

PRETREATMENT FEEDING STOMA — WHO ACTUALLY BENEFITED. This is the crux of the topic and the part most often oversimplified. Across the cohort as a whole, creating a gastrostomy or jejunostomy before chemoradiotherapy was NOT associated with longer progression-free or overall survival ^[2]. Benefit appeared only in the subgroup whose tumour occupied at least 70% of the lumen: less cachexia, better treatment response (odds ratio 2.78; P=0.028), longer median progression-free survival (6 vs 4 months; P=0.012) and longer median overall survival (11 vs 9 months; P=0.009) ^[2]. In patients with a smaller tumour-occupying proportion no benefit was found ^[2]. The authors draw a cautious conclusion: the tumour-occupying proportion may serve as a selection criterion for this invasive procedure, rather than as an argument for performing it in everyone ^[2].

STRENGTH OF EVIDENCE

Limited. In favour: the data come from a large, prospectively collected cohort with long follow-up, and tumour measurements were taken from standardised endoscopic images ^[2]; the statements on nutritional mechanisms and on early satiety after surgery rest on NCI's review ^[1]. Against full certainty: the key finding on feeding stomas comes from a SUBGROUP ANALYSIS of a non-randomised study — treating clinicians decided who received a stoma, so differences between groups may partly reflect that choice. The study concerns squamous cell carcinoma; evidence of comparable strength for oesophageal adenocarcinoma is lacking.

WHAT THIS ENTRY DOES NOT SAY

It does not indicate whether any individual patient should have a gastrostomy or jejunostomy, when, or in what form. That decision is made by the treating team — medical oncologist, radiation oncologist, surgeon and clinical dietitian — on the basis of endoscopic findings, nutritional status and the treatment plan. The service does not interpret individual clinical situations or test results.

Sources

1. [1] National Cancer Institute — PDQ: Nutrition in Cancer Care (Health Professional Version): cancer.gov ↗
2. [2] Pretreatment feeding-stoma placement in advanced esophageal cancer: defining optimal patient selection criteria. Esophagus 2026 (PMID 42165951, PMC13319426): europepmc.org ↗

WHAT HAPPENS AND WHY

Taste and smell changes are among the most frequently reported complaints during cancer treatment. Food may seem to have no flavour, meat may taste bitter or metallic, and food odours can become hard to tolerate. NCI lists as causes the treatment itself (chemotherapy, radiotherapy to the head and neck, immunotherapy), dental problems, and the cancer itself ^[1].

WHAT THE EVIDENCE SHOWS

A scoping review of 47 studies in head and neck cancer found that all 37 studies assessing taste reported some taste alteration after treatment. Agreement ends there: which taste qualities (sweet, sour, salty, bitter) were impaired, whether function returned to baseline, and which treatments were responsible varied across studies. For smell the findings were even less consistent — some studies found measurable impairment, others found none ^[2].

SUPPLEMENTS: WHAT WAS NOT CONFIRMED. Zinc sulfate was not found to be an effective treatment for taste impairment; a liposomal spray showed some potential, which the authors describe as a direction for research rather than a ready recommendation ^[2]. This should be distinguished from a different use of zinc with which it is often confused. A meta-analysis of five randomised trials (332 patients) addressed prevention of radiation-induced oral mucositis, not taste changes, and found the result depends on the route: systemic oral zinc does not provide a reliable prophylactic benefit, while topical zinc mouthwashes show an encouraging protective trend ^[3].

AT THE TABLE — NCI SUGGESTIONS ^[1].

• when food tastes metallic or bitter: use plastic, silicone, wooden or bamboo utensils instead of metal ones
• when meat has become unpalatable: plant-based protein sources such as tofu, nuts or beans
• when food seems to have no flavour: marinades for meat and fresh or dried herbs (basil, oregano, thyme)
• when odours are the problem: keep food covered until it is served and avoid strong smells such as brussels sprouts or fish

WHAT WE DO NOT KNOW

There is little research pointing to an effective treatment for taste and smell impairment — of the 47 studies in the review only three addressed treatment at all, and the authors name this explicitly as a gap ^[2]. Nor has it been established how far these changes worsen a patient's nutritional status. Persistent or worsening taste and smell changes are worth reporting to the treating team: they may have a cause requiring separate management, such as a dental problem.

Sources

1. NCI PDQ — Nutrition in Cancer Care (patient version): taste and smell changes: cancer.gov ↗
2. Smell and Taste Impairments in Head and Neck Cancer Patients — A Scoping Review, Nutrients 2025;17(6):1087: doi.org ↗
3. The Route of Administration Determines the Efficacy of Zinc in Preventing Radiation-Induced Oral Mucositis: A Systematic Review and Meta-Analysis, Curr Oncol 2026;33(6):371: doi.org ↗

WHERE THIS ADVICE CAME FROM

Low-fibre diets have historically been recommended during pelvic radiotherapy despite a lack of evidence — that is how the authors of the randomised trial in the American Journal of Clinical Nutrition describe the starting point ^[1]. The reasoning was mechanistic: fewer residues in the bowel, less stimulation of an irritated mucosa. For years the assumption was never tested under random allocation.

WHAT THE TRIAL THAT TESTED IT SHOWED

• 166 patients undergoing radical pelvic radiotherapy were randomly assigned to three arms: low-fibre (≤10 g non-starch polysaccharides/day), habitual-fibre (control) and high-fibre (≥18 g/day), each with individualised dietary counselling ^[1];
• fibre intakes did differ significantly between arms (P < 0.001), so the intervention worked as intended ^[1];
• THE PRIMARY ENDPOINT WAS NOT MET: the between-group difference in the change of the IBDQ-B bowel score from baseline to nadir was not significant (P = 0.093) ^[1];
• in further analyses the change from start to end of radiotherapy was smaller in the high-fibre arm (−3.7 ± 12.8) than in the habitual-fibre arm (−10.8 ± 13.5; P = 0.011), and at one year (n = 126) the scores were +0.1 ± 14.5 versus −8.4 ± 13.3 (P = 0.004) ^[1];
• no significant differences were found in stool frequency or form, nor in faecal short-chain fatty acid concentrations ^[1];
• significant reductions in energy, protein and fat intake occurred in the low-fibre and habitual-fibre arms ONLY ^[1].

HOW TO READ THIS HONESTLY

The primary endpoint was not met, so the trial does not prove that a high-fibre diet reduces bowel toxicity — the authors' conclusion rests on secondary measures and needs confirmation. What is robust is something else: the trial found no benefit from restricting fibre, and it did show a cost of that restriction, namely a fall in energy and protein intake in people already at risk of malnutrition. Hence the closing sentence of the paper: restrictive, non-evidence-based advice to reduce fibre intake in this setting should be abandoned ^[1].

WHAT THE SYSTEMATIC REVIEWS SAY

• a review of fibre modification in women with gynaecological cancers included 4 studies (89 participants in total) with quality ratings of neutral or negative; because of risk of bias, inconsistency, indirectness and imprecision, the GRADE certainty of evidence was rated VERY LOW and the body of evidence was judged insufficient to form specific recommendations for clinical practice ^[4];
• a broader review of dietary counselling during pelvic radiotherapy covered 11 randomised trials prescribing the consumption or avoidance of fats, fibre, lactose, protein and FODMAPs; three of them reported an improvement in the incidence of diarrhoea, results varied between studies, and the authors call for higher-quality trials ^[3].

WHEN RESTRICTING RESIDUE IS JUSTIFIED

This entry does not argue against a low-residue diet where it is a clinical indication — only against applying it ROUTINELY to every patient receiving radiotherapy. Situations in which the treating team advises a diet restricted in residue include narrowing or threatened obstruction of the gastrointestinal tract, the early period after bowel surgery and after stoma formation, and severe diarrhoea requiring immediate management. These are individual decisions based on examining the patient.

WHY A SPECIALIST SHOULD ASSESS THE SYMPTOMS

The 2025 British Society of Gastroenterology practice guidance (103 recommendations) stresses that long-term physical side effects of cancer therapy impinge on quality of life in up to 25% of those treated, and that gastrointestinal side effects are the most common and troublesome among them ^[2]. The guidance also makes two points that matter directly to patients: individual symptoms or symptom clusters are poor at distinguishing the underlying cause, and patients frequently have several coexisting gastrointestinal causes, all of which need to be diagnosed and optimally treated for symptoms to resolve ^[2]. The choice of management — dietary management included — belongs to the treating team, not to a general recommendation found online.

WHAT THIS ENTRY DOES NOT SAY

It contains no dietary recommendation for any individual and does not state how much fibre a patient should eat during radiotherapy. It states only where the evidence stands: automatic withdrawal of fibre is not supported by trials and may be paid for with poorer nutrition, while the evidence for the opposite direction is limited and requires confirmation. All the studies cited concern radiotherapy covering the pelvis and do not apply to irradiation of other body regions.

Sources

1. [1] Wedlake L i wsp. — Randomized controlled trial of dietary fiber for the prevention of radiation-induced gastrointestinal toxicity during pelvic radiotherapy, Am J Clin Nutr 2017 (166 chorych, trzy grupy; główny punkt końcowy p = 0,093; PMID 28679552, NCT01170299): europepmc.org ↗
2. [2] Andreyev J i wsp. — British Society of Gastroenterology practice guidance on the management of acute and chronic gastrointestinal symptoms and complications as a result of treatment for cancer, Gut 2025 (103 zalecenia; PMID 40068855): europepmc.org ↗
3. [3] The effect of nutritional interventions involving dietary counselling on gastrointestinal toxicities in adults receiving pelvic radiotherapy — a systematic review, J Med Radiat Sci 2021 (11 badań randomizowanych; PMID 34288532): europepmc.org ↗
4. [4] The Efficacy of Dietary Fiber in Managing Gastrointestinal Toxicity Symptoms in Patients with Gynecologic Cancers undergoing Pelvic Radiotherapy: A Systematic Review, J Acad Nutr Diet 2021 (4 badania, 89 uczestniczek, GRADE: bardzo niska pewność dowodów; PMID 33127328): europepmc.org ↗

WHAT IT IS

Enteral nutrition means delivering a prepared nutrient formula directly into the stomach or intestine through a tube — a narrow catheter passed through the nose or through the abdominal wall. Parenteral nutrition means delivering nutrients intravenously, bypassing the digestive tract altogether. Both serve the same purpose: meeting the needs of a patient who cannot meet them by eating.

WHEN IT IS CONSIDERED AT ALL

The National Cancer Institute PDQ summary ties nutrition support to the situation of a patient who is malnourished and unable, for a prolonged period, to take in adequate nutrients by mouth ^[1]. It is therefore not a dietary top-up "for strength", but a response to a specific, ongoing problem with food intake.

WHY THE ENTERAL ROUTE COMES FIRST

PDQ states the principle plainly: if the patient has a functioning gastrointestinal tract, enteral nutrition is the route used ^[1]. Feeding through the gut keeps it working and avoids the complications associated with central venous access. Parenteral nutrition is reserved for situations in which the gut does not work or is obstructed.

HAEMATOPOIETIC CELL TRANSPLANTATION — THE ONE EXPLICIT TIME THRESHOLD. For patients undergoing haematopoietic cell transplantation, PDQ gives a concrete criterion: nutrition support is given to those who are malnourished and expected to be unable to ingest or absorb adequate nutrients for a prolonged period, defined as more than 7-14 days ^[1]. This is the only figure the source states in this context, and it applies only to this group of patients.

WHAT IT DOES NOT SOLVE

Nutrition support is not a cancer treatment and does not replace anticancer therapy. PDQ presents no evidence for routinely adding it to standard chemotherapy or radiotherapy in patients who are eating adequately; for that period it puts symptom control and practical coping strategies first ^[1].

WHAT IS OUTSIDE THE SCOPE OF THIS PAGE

Detailed starting thresholds, choice of formula, rate of delivery and prevention of refeeding complications are matters for clinical guidelines and individual assessment — they belong to the treating team and the responsible physician, not to an information page. This page describes what these methods are and the logic by which they are ordered, not when any particular person should use them.

SOURCES.

• ^[1] National Cancer Institute, PDQ Nutrition in Cancer Care (health professional version)

Sources

1. National Cancer Institute — PDQ Nutrition in Cancer Care (health professional version): cancer.gov ↗

WHY THIS ENTRY EXISTS

Throughout this service the message recurs that malnutrition in cancer must not be dismissed. This page addresses the other side of the same problem: bringing someone out of prolonged starvation is a separate medical task, and haste in it can be more dangerous than the deficit itself. It is one of the few situations in clinical nutrition where faster does not mean better.

WHAT THE PHENOMENON IS

During prolonged starvation the body switches to burning fat, and stores of phosphate, potassium and magnesium become depleted — even though their blood concentrations may appear normal ^[3]. When feeding resumes, rising glucose stimulates insulin secretion, and insulin drives phosphate, potassium and magnesium from the blood into cells; at the same time increased glucose metabolism consumes thiamine (vitamin B1) stores ^[3]. The classic laboratory feature is a fall in phosphate, but the picture also includes disturbed sodium and fluid balance and deficiency of thiamine, potassium and magnesium ^[1][2].

WHY IT MATTERS

The reported consequences can be severe and affect several systems at once ^[3]:

• heart — arrhythmias, low blood pressure, in extreme cases cardiac arrest;
• respiratory system — respiratory failure, pulmonary oedema;
• nervous system — features of thiamine deficiency (confusion, memory impairment, disturbed balance and eye movements).

For this reason, feeding is restarted under laboratory monitoring rather than by impression.

WHOM IT CONCERNS IN ONCOLOGY

The risk relates not to the diagnosis itself but to the DURATION AND DEPTH of reduced intake ^[1]. In oncological practice this usually means situations in which eating has been physically difficult or impossible for weeks: narrowing of the oesophagus or stomach, bowel obstruction, severe dysphagia after treatment of head and neck cancer, intractable vomiting, and advanced cancer cachexia. Additional risk factors include low body mass index, unintentional weight loss, previous starvation, past alcohol misuse and low baseline electrolyte levels ^[3].

WHAT THE TREATING TEAM DOES

The ESPEN guideline describes increasing nutritional provision slowly over several days and supplying vitamin B1 together with a balanced micronutrient mixture before and during repletion; potassium, phosphate and magnesium are monitored and replaced as needed ^[1][2]. We deliberately give NO doses or threshold values here — these are set individually from body weight, laboratory results and route of administration, and quoting them outside the clinical context would amount to advice for an individual rather than a description of knowledge.

HOW STRONG IS THE EVIDENCE

The ESPEN recommendation to advance nutrition slowly carries a strong grade but rests on a LOW level of evidence and on expert consensus ^[1][2]. The mechanism is well described physiologically and clinically ^[3], whereas trials comparing different refeeding schedules are few — which is why we tagged this entry as based on limited evidence. That does not mean the hazard is doubtful; it means there is no single schedule proven in trials.

WHAT THIS ENTRY DOES NOT SAY

It does not say after how many days without eating the risk appears in a given person, nor how many calories may be given on the first day. Nor is it a reason to postpone nutritional treatment — on the contrary: malnutrition in cancer requires treatment, and knowledge of refeeding syndrome exists so that it can be treated safely.

THE DECISION BELONGS TO THE DOCTOR

Whether a person is at risk of refeeding syndrome, and how fast to advance feeding, is decided by the treating specialist together with the nutrition team. If a patient has eaten very little for a prolonged period, it is worth telling the treating team BEFORE intensive refeeding begins — including when it takes place at home with oral nutritional supplements.

Sources

1. [1] Muscaritoli M i wsp. — ESPEN practical guideline: Clinical Nutrition in cancer. Clin Nutr 2021;40(5):2898-2913 (PMID 33946039) — zalecenie powolnego, rozłożonego na kilka dni zwiększania żywienia po długotrwale zmniejszonym przyjmowaniu pokarmu; siła zalecenia wysoka, poziom dowodów niski (konsensus): pubmed.ncbi.nlm.nih.gov ↗
2. [2] ESPEN — ESPEN practical guideline: Clinical Nutrition in cancer (pełny tekst wytycznych, espen.org) — hipofosfatemia jako klasyczna cecha zespołu; profilaktyczna podaż witaminy B1 i mieszanki mikroelementów; monitorowanie potasu, fosforanów i magnezu: espen.org ↗
3. [3] Persaud-Sharma D, Saha S, Trippensee AW — Refeeding Syndrome. StatPearls, NCBI Bookshelf (NBK564513) — definicja, mechanizm (wyrzut insuliny, przesunięcie fosforanów/potasu/magnezu do komórek, zużycie tiaminy), czynniki ryzyka i następstwa sercowe, oddechowe i neurologiczne: ncbi.nlm.nih.gov ↗

WHAT THE EVIDENCE SHOWS

A meta-analysis published in Nutrients (2026) on adherence to the Mediterranean diet AFTER a cancer diagnosis, with emphasis on colorectal cancer, included eight studies ^[2]. Six prospective cohort studies (6,697 participants in total) assessed recurrence: higher adherence was associated with a lower risk of recurrence or cancer-specific death (HR 0.83; 95% CI 0.70-0.99; I2 = 49%, i.e. moderate heterogeneity) ^[2]. Two randomised trials (76 participants in total) assessed cancer-related fatigue and found no significant effect (MD 0.29; 95% CI -0.58 to 1.16 — the interval includes zero) ^[2]. The authors themselves note that both results are limited by the small number of studies and methodological heterogeneity, and describe the fatigue evidence as exploratory and statistically imprecise ^[2].

STRENGTH OF EVIDENCE

Moderate and largely observational. That distinction matters most here: in cohort studies, people who eat this way are also more likely to be physically active, not to smoke and to have better access to care — each of which improves prognosis on its own. The result must therefore not be read as "the Mediterranean diet lowers recurrence risk by 17%" ^[2]. For primary prevention the NCI position is more cautious still: population studies have not yet shown definitively that any dietary component causes or protects against cancer ^[1].

WHAT IS WELL DOCUMENTED

One element of this pattern is limiting alcohol, and here the evidence is strong and points the other way: according to the NCI, heavy or regular alcohol consumption INCREASES the risk of cancers of the oral cavity, pharynx, larynx, oesophagus, liver, breast, colon and rectum ^[1]. If one dietary decision has the best-documented bearing on cancer risk, it is limiting alcohol — not selecting "anticancer" foods.

WHO IT SUITS

The pattern aligns with general healthy-eating advice and as such is safe for most people, including during and after cancer treatment. Exceptions need individual assessment: patients with malnutrition or cachexia need an energy- and protein-dense diet rather than a restrictive one, and patients with neutropenia, mucositis, diarrhoea or recent gastrointestinal surgery receive separate advice from their treating team.

WHAT THIS DIET DOES NOT DO

It does not treat cancer and does not replace cancer treatment. None of the studies cited tested the diet as anticancer therapy, and diet is never a reason to delay or modify treatment.

Sources

1. National Cancer Institute — Risk Factors: Diet, cancer.gov 2024: cancer.gov ↗
2. Papamichael D, Felekkis K, Andreou EP — Post-Diagnosis Adherence to the Mediterranean Diet and Cancer Recurrence and Fatigue Outcomes in Cancer Survivors, with Emphasis on Colorectal Cancer: A Systematic Review and Meta-Analysis, Nutrients 2026 (PMID 41829977): europepmc.org ↗

WHY IT IS DONE

Quoting the NCI: extra protein and calories help keep your strength up to deal with the side effects of treatment, prevent malnutrition and maintain the best possible quality of life ^[1]. The second argument is purely practical and often underrated: staying nourished increases the chance of receiving treatment without unplanned breaks — and interruptions to chemotherapy or radiotherapy carry a cost.

WHAT IS ADVISED IN PRACTICE

The NCI's advice during treatment runs counter to popular notions of an "anticancer diet": meals rich in protein and calories, smaller portions more often (around five to six a day rather than three large ones), adapting food to the taste and smell changes that commonly accompany treatment, and food safety precautions while immunity is weakened ^[1]. Menu planning belongs to a registered dietitian within the treating team ^[1].

CANCER CACHEXIA

This is not the same as poor appetite. The NCI describes it as a wasting syndrome causing weakness, weight loss and loss of fat and muscle, which can occur even when a person is eating well ^[1]. The implication matters: simply eating more does not reverse cachexia, and its diagnosis and management belong to the treating team rather than to self-directed attempts.

WHEN EATING IS NOT ENOUGH

Artificial nutrition support (delivery through a feeding tube, or intravenously when the gastrointestinal tract cannot be used) is an option for people who cannot eat or digest enough food to stay nourished ^[1]. This is a clinical decision, made individually and depending on the situation, including tumour type and planned treatment ^[1].

WHAT THIS ENTRY DOES NOT CONTAIN

We do not give protein or calorie requirements per kilogram of body weight, although such figures appear in nutrition society guidelines — we could not confirm them in the source available to us, and an unverified number is worse than none. Requirements are set individually by a clinical dietitian ^[1].

Sources

1. National Cancer Institute — Nutrition During Cancer Treatment, PDQ 2024: cancer.gov ↗

WHAT IT IS

An international expert panel (Lancet Oncology, 2011) defined cancer cachexia as a multifactorial syndrome of ongoing loss of skeletal muscle mass — with or without loss of fat mass — that CANNOT be fully reversed by conventional nutritional support and leads to progressive functional impairment ^[1]. It is driven by a negative protein and energy balance arising from a variable combination of reduced food intake and abnormal metabolism ^[1]. That last part is the key to this entry: cachexia is not simply undereating. The National Cancer Institute puts it plainly: wasting "can occur even when you are eating well" ^[4].

HOW IT IS DIAGNOSED

The agreed criterion is weight loss greater than 5%, or greater than 2% in people already depleted by body-mass index (below 20 kg/m²) or by skeletal muscle mass (sarcopenia) ^[1]. The consensus describes stages — precachexia, cachexia and refractory cachexia — and states that assessment should cover four domains: anorexia or reduced food intake, catabolic drive, muscle mass and strength, and functional and psychosocial impairment ^[1].

HOW COMMON, AND HOW OFTEN MISSED. A retrospective record analysis of 76 547 cancer patients (Journal of Cachexia, Sarcopenia and Muscle, 2026) found cachexia in 2.42% of the whole cohort but in 29.3% of 6946 patients with colorectal, pancreatic or bronchial/lung cancer ^[2]. What matters most is what the authors found inside the records themselves: ICD coding identified 620 patients and free-text analysis a further 1507; in addition, 1340 patients had a BMI below 20 or more than 5% weight loss yet were not coded as cachectic ^[2]. The authors conclude that standard coding substantially underestimates the prevalence of cachexia ^[2].

WHY IT MATTERS TO THE PATIENT

A systematic review of 37 studies covering 52 053 patients with solid tumours (Journal of Cachexia, Sarcopenia and Muscle, 2026) found cachexia associated with worse physical function (a statistically significant association in 25 of 31 studies, 80.6%), worse health-related quality of life (22 of 24, 91.7%), worse performance status (14 of 16, 87.5%) and worse activities of daily living (6 of 6) ^[3]. The same review exposed a real limitation of the literature: eleven different definitions of cachexia were used, and the 2011 consensus criteria in only 45% of studies, so comparisons between studies carry uncertainty ^[3].

THE SCOPE OF WHAT WE WRITE HERE

We deliberately do NOT give calorie targets, grams of protein per kilogram, or enteral and parenteral feeding regimens. Those decisions belong to the treating team and clinical dietitian, because they depend on the diagnosis, the stage of treatment, gut function and comorbidities. Nor do we know of — and we did not find in reference-class sources — any diet or supplement that can honestly be said to reverse cachexia; the consensus definition itself states that conventional nutritional support does not ^[1]. Offers of "anti-wasting diets" and muscle-rebuilding preparations therefore call for particular caution: a promise that the best-documented nutritional intervention does not keep will not be kept by a product sold without such documentation.

WHAT FOLLOWS IN PRACTICE

Early recognition matters, because the consensus describes a precachexia stage preceding the full syndrome ^[1]. Weight loss is measurable and worth recording — the record-based data show it is often present in measurements yet never reaches the diagnosis ^[2]. Raising unintended weight loss with the treating team is therefore reasonable even when the patient "is eating normally" ^[4].

Sources

1. Fearon K i wsp. — Definition and classification of cancer cachexia: an international consensus, The Lancet Oncology 2011: europepmc.org ↗
2. Colardelle Y i wsp. — Cancer Cachexia Prevalence Is Underestimated in Medical Records of Patients in a Regional Tertiary Hospital, Journal of Cachexia, Sarcopenia and Muscle 2026: europepmc.org ↗
3. Crawford J i wsp. — Functional Outcomes and Quality of Life for Patients With Cachexia and Solid Tumour Cancers: Findings of a Systematic Literature Review, Journal of Cachexia, Sarcopenia and Muscle 2026: europepmc.org ↗
4. National Cancer Institute — Nutrition During Cancer Treatment, cancer.gov 2024: cancer.gov ↗

WHAT THE INSTITUTIONS RECOMMEND

In Diet, Nutrition, Physical Activity and Cancer (2018) the World Cancer Research Fund recommends that wholegrains, non-starchy vegetables, fruit and pulses form the basis of the everyday diet. The numerical goals are at least 30 g of dietary fibre from food per day and at least five portions, totalling a minimum of 400 g, of a variety of non-starchy vegetables and fruit per day ^[1]. Non-starchy vegetables are vegetables other than potatoes, sweet potatoes and other starchy tubers.

HOW STRONG IS THE EVIDENCE - THE DISTINCTION THAT USUALLY GETS LOST. WCRF grades its evidence, and for vegetables and fruit it did not award the highest grade:

• evidence in the strong category (probable) applies to the combined effect of non-starchy vegetables and fruit on aerodigestive cancers considered as one group;
• for individual cancer sites the grade falls to limited-suggestive. Non-starchy vegetables: mouth, pharynx and larynx, nasopharynx, oesophagus (adenocarcinoma and squamous cell carcinoma), lung in people who smoke or used to smoke, and oestrogen-receptor-negative breast cancer. Fruit: squamous cell carcinoma of the oesophagus and lung cancer in people who smoke or used to smoke ^[1];
• the limited-suggestive category means the findings are broadly consistent in direction but rarely sufficient to justify recommendations for reducing cancer risk ^[1].

WHAT NCI SAYS ABOUT CRUCIFEROUS VEGETABLES

In its fact sheet on cruciferous vegetables (broccoli, cabbage, Brussels sprouts, cauliflower) the National Cancer Institute states that human studies have shown mixed results ^[2]. For prostate cancer, large cohort studies found little or no association, although some case-control studies suggested a lower risk. For colorectal, lung and breast cancer the picture is similarly inconsistent, and a meta-analysis in breast cancer found no association. NCI presents cruciferous vegetables as part of overall vegetable intake rather than as a separate risk-reducing measure ^[2].

WHY THE RECOMMENDATION IS NEVERTHELESS FIRM

The value of this food group does not rest solely on a direct effect on cancer risk. A diet rich in vegetables, fruit and wholegrains makes it easier to maintain a healthy body weight, and excess body weight is one of the best-documented nutritional risk factors for cancer ^[1]. Separate, strong evidence links dietary fibre and wholegrains to a lower risk of colorectal cancer ^[1] - this catalogue covers that in its own entry.

WHAT THIS ENTRY DOES NOT SAY

There is no evidence that vegetables or fruit treat cancer or replace any form of treatment. Nor is there a basis for singling out any individual product as anticancer - the evidence concerns the overall dietary pattern rather than single components. Nutrition during cancer treatment, in particular in malnutrition, swallowing disorders, neutropenia or after gastrointestinal surgery, is determined by the treating physician together with a clinical dietitian.

WHAT THE RECOMMENDATION COVERS

In Diet, Nutrition, Physical Activity and Cancer (2018) the World Cancer Research Fund frames it as limiting consumption of processed foods high in fat, starches or sugars, including foods described as fast foods ^[1]. It concerns energy-dense products that make it easy to exceed energy requirements, rather than one category of dish or any particular restaurant chain.

HOW STRONG IS THE EVIDENCE

• Strong evidence: diets containing greater amounts of fast foods and other processed foods are a cause of weight gain, overweight and obesity, because they increase the risk of excess energy intake ^[1].
• Probable evidence: consuming fast foods is a cause of weight gain, overweight and obesity; the same applies to a Western-type diet as an overall dietary pattern ^[1].
• Probable evidence, this time for CANCER directly: a high dietary glycaemic load is a cause of endometrial cancer ^[1].

WHY THE RECOMMENDATION STILL MATTERS ALTHOUGH THE LINK IS INDIRECT. For most cancers the effect of this food group has not been demonstrated directly - it runs through body weight. That indirect route is not a weak one: excess body weight is among the best-documented nutritional risk factors for cancer and is linked to more than a dozen diagnoses. This catalogue covers it in a separate entry that lists the specific cancers together with their qualifications (for example, breast cancer only after the menopause). Limiting highly processed foods is therefore a tool for maintaining body weight, not a standalone anticancer measure.

WHAT THIS ENTRY DOES NOT SAY

There is no evidence that a single fast-food meal increases cancer risk, or that avoiding one protects against the disease. The recommendation concerns a sustained dietary pattern, not isolated episodes. The opposite situation deserves separate attention: in patients with malnutrition or cancer cachexia, restricting energy intake can be harmful, and nutrition during cancer treatment is determined by the treating physician together with a clinical dietitian - this catalogue describes prevention at population level, not management of an individual person.

WHAT IT IS AND WHERE THE IDEA COMES FROM. The ketogenic diet sharply restricts carbohydrate in favour of fat, moving the body into nutritional ketosis. The biological rationale is real and named in the literature: many tumour cells, and glioblastoma in particular, show the Warburg effect — a dependency on aerobic glycolysis for energy ^[1]. The authors of a 2026 review in Neurological Sciences describe this as a "metabolic vulnerability" the diet is meant to exploit ^[1]. A biological rationale, however, is not the same thing as clinical proof, and this entry is precisely about that distinction.

WHAT THE GLIOBLASTOMA DATA SHOW

A PRISMA-compliant systematic review (Neurological Sciences 2026, PROSPERO CRD420251232650) included 41 studies published up to September 2025 — from randomised trials to case series and conference abstracts ^[1]. Adherence was high: more than 75% of participants maintained nutritional ketosis ^[1]. In adherent cohorts, median overall survival was 29.4 months versus 14.6 months in historical controls, with a 66.7% three-year survival rate ^[1]. The authors themselves conclude that standardised phase 3 trials are needed — and that is the most important sentence in the review ^[1].

WHY THOSE NUMBERS CALL FOR CAUTION

First, the comparator is a HISTORICAL control: survival reported in other studies and other years, not a group randomly allocated to standard care ^[1]. Second, the review included case series and abstracts, a literature in which favourable results are the ones that get published ^[1]. Third — the caveat a patient will not find in headlines — people able to sustain a restrictive diet for many months are by definition in better general condition, and better performance status is itself associated with longer survival in glioblastoma. From such a comparison it is not possible to say how much of the gap between 29.4 and 14.6 months belongs to the diet and how much to who was able to follow it ^[1].

WHAT IS KNOWN BEYOND GLIOBLASTOMA

An umbrella review in Integrative Cancer Therapies (2026) screened 615 articles and examined 24 systematic reviews and meta-analyses of the ketogenic diet in cancer ^[2]. The findings cut both ways: the diet improved metabolic markers — glucose and triglycerides — and showed benefits for body composition and quality of life, while evidence on treatment-related complications, including radiotherapy side effects, is described by the authors as limited and heterogeneous ^[2]. Their conclusion is that the diet shows promise as a safe and effective ADJUNCTIVE therapy and that more evidence is needed before firm conclusions can be drawn ^[2]. There is no claim of tumour control ^[2].

SAFETY. In the glioblastoma review the diet was well tolerated: adverse events were limited to mild gastrointestinal symptoms and fatigue, with no grade 3 or 4 diet-related toxicity reported ^[1]. That is meaningful, but it describes trial participants — people who were selected and monitored. A separate and unresolved issue is the risk of weight loss in patients already at risk of wasting; a ketogenic diet by design restricts energy from one macronutrient, and unintended weight loss is a marker of poor prognosis in oncology (see our entry on nutrition in cancer cachexia).

WHAT THE REFERENCE SOURCE SAYS

The National Cancer Institute, on its page about complementary approaches, states plainly that "there is no food or special diet that has proved to control cancer", and advises telling your doctor about any complementary approach you use ^[3]. That sentence does not rule out studying the ketogenic diet as supportive care — it rules out treating it as cancer therapy.

THE SCOPE OF WHAT WE WRITE HERE

We do not give macronutrient ratios, protocols for inducing ketosis, or target ketone levels. In cancer, a ketogenic diet affects body weight, glucose metabolism and treatment tolerance, so it belongs in the hands of the treating team and a clinical dietitian — particularly for people with diabetes, kidney disease, malabsorption or ongoing weight loss. We also found no high-quality data on interactions between the ketogenic diet and specific chemotherapy regimens, and we do not fill that gap with conjecture.

Sources

1. Firdous J, et al. — Efficacy and safety of ketogenic diet in glioblastoma: an updated systematic review and meta-analysis, Neurological Sciences 2026 (PMID 42032215): europepmc.org ↗
2. Kamali M, et al. — The Effect of a Ketogenic Diet on Cancer: Evidence From Systematic Reviews and Meta-Analyses, Integrative Cancer Therapies 2026 (PMID 41782309): europepmc.org ↗
3. National Cancer Institute — Complementary and Alternative Medicine (CAM) in Cancer Treatment, cancer.gov 2024: cancer.gov ↗

WHAT THIS ENTRY COVERS

This is about nutritional management delivered by the treating team around planned cancer surgery, especially of the gastrointestinal tract. It comprises three distinct things that should not be conflated: assessment of nutritional risk before surgery, shortening the fasting period and returning to oral intake early after surgery, and so-called immunonutrition formulas (enriched with arginine, omega-3 fatty acids and nucleotides, among others). The first two are part of standard perioperative care; the third is an add-on intervention, and it is the subject of most of the studies cited here.

WHAT THE EVIDENCE SHOWS

An umbrella review of 54 meta-analyses in patients undergoing cancer surgery (BMC Cancer, 2026) reported, in favour of immunonutrition:

• overall complications RR 0.79 (95% CI 0.70–0.88)
• infectious complications RR 0.61 (0.58–0.65)
• surgical-site infection RR 0.66 (0.59–0.74)
• mortality HR 0.86 (0.74–0.99)
• length of hospital stay shorter by a mean of 1.75 days (–2.09 to –1.41)

The ESPEN guideline on clinical nutrition in surgery (2025 update) states the general principles: start nutritional therapy as soon as nutritional risk becomes apparent, avoid long periods of preoperative fasting, and re-establish oral feeding, the preferred route, as early as possible after surgery.

WHERE THE SOURCES DIVERGE — AND WHY WE SAY SO PLAINLY. A meta-analysis of 9 randomised trials in colorectal cancer (1,198 patients, Frontiers in Nutrition, 2026) confirms the reduction in infections (OR 0.48; 0.34–0.66) but does NOT confirm an effect on anastomotic leak, postoperative ileus or length of stay — precisely the endpoints where the umbrella review sees benefit. We resolve this in favour of the more cautious reading, on two methodological grounds. First, an umbrella review pools meta-analyses that partly rest on the same primary trials, so a single result can be counted several times. Second, its length-of-stay estimate has heterogeneity of I² = 90.3%, meaning the individual studies disagree strongly and the averaged figure is unstable. One effect is reproducible across both sources: fewer infectious complications.

WHAT THESE RESULTS DO NOT SAY

They do not say that an immunonutrition formula replaces ordinary food, or that it improves cancer prognosis in itself — the endpoints measured concern the perioperative course, not cure of the tumour. Nor do they establish when to start: the observation that postoperative administration outperforms preoperative administration comes from a subgroup analysis and is therefore a hypothesis, not a finding. Finally, they say nothing about people who are not undergoing surgery.

SAFETY AND INTERACTIONS

Immunonutrition is a medical product used under hospital care, not a supplement bought independently; its composition (notably high arginine doses) has been questioned in patients with sepsis and severe organ failure. After gastrointestinal surgery, the route of delivery (oral, nasoenteric tube, jejunostomy) and the rate of volume escalation are part of the surgical plan. Whether, when and in what form nutritional support is introduced is decided by the treating team — the surgeon together with a clinical dietitian.