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.

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 ↗

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 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 ↗

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 ↗

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 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.