Key points
- During treatment the body often needs more protein and calories; good nutrition for people with cancer can be different from the usual "healthy diet" [1].
- Malnutrition and muscle loss are common in people with cancer and harm the results of treatment; every patient should be checked regularly for the risk of malnutrition [3].
- The ESPEN guideline recommends combining nutritional care with physical activity and exercise [3].
- Taking antioxidant, iron or vitamin B12 supplements during chemotherapy was linked with worse results in one study; talk to your doctor before taking any supplement (apart from an ordinary multivitamin) [7].
- When your white blood cells are low, food safety (cooking meat and eggs thoroughly, washing fruit and vegetables) matters [9].
- Always tell your care team about unplanned weight loss, being unable to eat or drink for a few days, or signs of dehydration [1].
Why does nutrition matter in cancer treatment, and what gets in the way?
Enough protein and calories help you keep the strength to cope with treatment side effects, prevent malnutrition and have the best possible quality of life [1]. Malnutrition can come from eating too little, less physical activity and metabolic changes caused by the tumour [3]. If malnutrition is not managed, it can lead to cachexia: a syndrome of weakness, weight loss and loss of fat and muscle that can happen even when you eat enough [1].
Treatment side effects that affect nutrition [1]:
- Chemotherapy: poor appetite, nausea and vomiting, constipation or diarrhoea, dry and sore mouth, taste changes, difficulty swallowing, feeling full quickly.
- Radiotherapy: depending on the area, anything from a dry and sore mouth to difficulty swallowing, nausea and diarrhoea; most side effects appear 2 to 3 weeks after it starts.
- Hormone therapy: weight gain, fluid retention and raised blood sugar.
- Immunotherapy and targeted therapy: tiredness and poor appetite, diarrhoea, nausea and taste changes.
Cancers of the head and neck, oesophagus, stomach, pancreas, liver and bowel are more often linked with nutrition problems [1].
What helps?
Practical tips
- 1
Plan before treatment
Stock your fridge and kitchen with high-protein, high-calorie foods and ready or easy meals; cook ahead and freeze food in small portions; keep light snacks such as plain biscuits or crackers to hand, and accept offers of help with shopping and cooking from your family [1].
- 2
Small, frequent meals
Eat five or six small meals a day, and have your biggest meal when your appetite is best [1].
- 3
Protein first
Eat high-protein foods at the start of a meal and add protein and calories to your food. Meat, fish, eggs, dairy foods and plant proteins such as beans and lentils are good sources [1].
- 4
Drink between meals
Drink most of your fluids between meals rather than with food (small sips with meals are fine). If you do not feel like solid food, try shakes, smoothies, soup or juice [1].
- 5
Oral nutritional supplements
If you cannot keep your weight up with ordinary food, nutritional supplement drinks (high in energy and protein) help [1]. Ask a dietitian which type suits you.
- 6
- 7
Work with a dietitian
If you are at risk of malnutrition, your doctor will refer you to a dietitian, who will make an eating plan that fits your side effects and needs [1].
Food safety during treatment
Cook thoroughly
Cook meat, fish and eggs thoroughly [9].
The right temperature
Keep hot food hot and cold food cold [9].
Wash and keep apart
Wash raw fruit and vegetables well and use separate dishes and boards for raw meat and vegetables [1].
A strict diet is not needed
In a careful study of patients with leukaemia, cutting out raw fruit and vegetables completely did not reduce serious infections [8].
What can your doctor do?
Show detailsHide
If you have trouble eating, your care team will ask about weight changes, how much and what kind of food you eat, eating problems and your ability to do daily activities, and refer you to a dietitian if needed [1]. Nutritional help is given step by step: from dietary advice and oral supplements to tube feeding or intravenous nutrition if needed [1, 3]. For severe loss of appetite in advanced cancer, appetite-boosting medicines such as progesterone-like drugs or a short course of corticosteroids may be tried [5].
For physicians
Guideline summary for physicians
- ESPEN 2017: regular screening of all patients for the risk or presence of malnutrition; meeting energy and nutrient needs step by step from counselling to parenteral nutrition (except in end-of-life care), weighing benefit and harm in advanced disease; combining nutritional care with exercise training; drugs and pharmaconutrients have limited effect on malnutrition in advanced cancer [3]. In the guideline text, total energy needs are usually taken as 25 to 30 kcal/kg/day and protein intake above 1 and, if possible, up to 1.5 g/kg/day [3].
- ESPEN practical guideline 2021: 43 practical recommendations as flowcharts for nutritional diagnosis and management [2].
- ASCO 2020 (cachexia in advanced cancer): dietary counselling may be offered; enteral tube feeding and parenteral nutrition should not be used routinely; no specific drug is standard of care, but if a drug trial is chosen, progesterone analogues and short-term corticosteroids (a few weeks) can be used [5]. ESMO also recommends screening, assessment and multimodal management of cachexia [4].
- Supplements: in a prospective study alongside the SWOG S0221 trial (1134 patients with breast cancer), antioxidant use before and during chemotherapy was associated with a higher risk of recurrence (adjusted HR 1.41; 95% CI 0.98 to 2.04; P=0.06); vitamin B12 was associated with worse disease-free survival (HR 1.83) and iron during chemotherapy with recurrence (HR 1.79); multivitamins were not associated with outcome [7].
- ACS 2022: nutrition and physical activity guideline for cancer survivors, including recommendations for the treatment period [6].
Myths and facts
| Common belief | Fact |
|---|---|
| During treatment you should eat a light, low-calorie diet. | Many patients need more protein and calories during treatment [1]; restrictive diets can make malnutrition worse [3]. |
| During chemotherapy you must not eat any fresh fruit or vegetables. | Cutting out raw fruit and vegetables completely did not reduce serious infection in a careful study [8]; washing them thoroughly and following food safety rules is enough [1]. |
| If I eat well, I will not get cachexia. | Cachexia can happen even when you eat enough, because part of it comes from metabolic changes caused by the tumour [1, 3]. |
When should I call my doctor?
- Unplanned weight loss, or you cannot keep your weight up despite trying [1].
- You cannot eat or drink enough, or you have ongoing vomiting or diarrhoea; there is a risk of dehydration and malnutrition [1].
- Pain or sores in the mouth and throat that stop you eating [1].
- A temperature of 38 °C or higher during chemotherapy, or diarrhoea with a fever; this is an emergency [9].
Frequently asked questions
I have no appetite; what can I do?
Can I take herbal remedies or supplements?
Talk to your doctor before taking any supplement or herbal remedy; some may interact with your treatment, and some supplements have been linked with worse results [7].
References
9 referencesShow all references, 7 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2ESPEN practical guideline: Clinical Nutrition in cancer
- 3
- 4Cancer cachexia in adult patients: ESMO Clinical Practice Guidelines
- 5
- 6American Cancer Society nutrition and physical activity guideline for cancer survivors
- 7
- 8Randomized Comparison of Cooked and Noncooked Diets in Patients Undergoing Remission Induction Therapy for Acute Myeloid Leukemia
- 9
This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/guides/nutrition-during-treatment/