Eating during cancer treatment: managing side effects

What should you eat if chemotherapy makes you feel or be sick?

Nausea is one of the most common side effects of chemotherapy. The US National Cancer Institute (NCI) advises against forcing yourself to eat large amounts and recommends taking only small sips during meals. Eating and drinking at the same time may make you feel full sooner. Have water, herbal tea or broth half an hour before or after eating [2]. If you feel sick when you wake up, toast, rusks or plain biscuits before getting out of bed may settle your stomach, as the NCI advises [2]. For questions about the prostate, see “Prostate and diet”.

Food temperature and smell can make a big difference. Very hot food gives off more aroma, and strong smells can trigger nausea. The NCI advises choosing food that is neither very hot nor very cold and avoiding cooking smells [2]. Try rice salads, lukewarm vegetable soups or ripe fruit. Ask someone else to cook if smells upset your stomach, and air the room well before sitting down to eat.

If vomiting does not settle, your medical team may adjust your anti-sickness medicines (antiemetics).

How can you adapt food if you have mouth sores or pain when swallowing?

Mucositis is inflammation of the lining of the mouth, causing sores and pain. It can occur with chemotherapy or radiotherapy to the head and neck. The NCI recommends cooking food until tender and cutting it into small pieces or puréeing it to make eating less painful [2]. Choose soft, moist or puréed foods: enriched vegetable soups, purées with poached egg, flaked white fish, plain yoghurt and cottage cheese.

Avoid foods that irritate a sore mouth: citrus fruit, tomatoes and ketchup, and spicy foods. Hard or crunchy foods such as whole nuts, crisps or bread crusts may also rub against it [2]. Very hot food can hurt more; lukewarm or cold dishes and sucking ice, as the NCI advises, may soothe the area [2].

Look after your oral hygiene. The NCI suggests rinsing with a glass of lukewarm water containing a quarter teaspoon of baking soda and a pinch of salt. Avoid alcohol-based mouthwashes, which can sting damaged tissue [2].

What can you do if food tastes metallic or bland?

Dysgeusia is a change in taste caused by chemotherapy medicines and radiotherapy. A persistent metallic taste is common, or everything may taste bland or bitter. The US National Cancer Institute (NCI) suggests a simple option: use plastic cutlery and avoid drinking directly from cans or metal containers [2]. Wooden or bamboo cutlery works too.

Red meat is often the food that tastes worst during treatment. Do not force yourself to eat it: the NCI says you can replace it with poultry, fish, eggs or cheese [2], as well as tofu or puréed pulses. If food tastes of nothing, the NCI suggests serving meat with something sweet, such as apple purée, or marinating it with herbs and spices [2]. Try thyme, basil or rosemary, provided you do not have mouth sores.

Rinsing your mouth before and after meals, as the NCI advises, may help remove the unpleasant taste and make food easier to taste [2].

How can you manage treatment-related diarrhoea?

Diarrhoea caused by treatment can quickly lead to dehydration and reduce nutrient absorption. The NCI advises drinking plenty of fluids to replace losses and choosing foods rich in sodium and potassium, such as broth, banana or baked potato [2]. Sip water, oral rehydration solution from a pharmacy, rice water or defatted broth throughout the day.

Choose low-fibre foods that are easy to digest: white rice, boiled potatoes, cooked carrots, and grilled or steamed chicken or white fish. You can also have a ripe banana and baked or stewed apple. If you have diarrhoea, temporarily reduce the foods the NCI identifies as aggravating it: wholegrains, pulses and gas-producing vegetables such as cabbage or cauliflower. Also reduce fried and fatty foods, spicy foods, lactose-containing dairy products and sugar-free products containing sorbitol or xylitol [2].

Also avoid alcohol, which may worsen diarrhoea. Once your bowel movements return to normal, gradually reintroduce fibre, starting with cooked fruit and oats.

What can you do about constipation during chemotherapy or radiotherapy?

Constipation during treatment is not always caused by food. It is often caused by some anti-sickness medicines, such as ondansetron (Zofran), opioid painkillers or moving around less. Do not take laxatives on your own; discuss it with your medical team first, as they can adjust them to your treatment.

For dietary measures, the NCI recommends drinking plenty of fluids each day, eating more fibre-rich foods and staying active [2]. Gradually increase fibre with cooked oats, ground flaxseed, green beans, squash and fruit such as plums, pears or kiwi. Spread water, herbal tea or warm broth throughout the day, unless your team has restricted your fluids. For more ideas, see our constipation diet guide.

Walk each day as your strength allows, as the NCI advises [2]. If constipation lasts several days or severe abdominal pain develops, tell your oncology team before changing your plan.

How can you eat if you have no appetite or feel full quickly?

Loss of appetite and feeling full quickly are common with cancer and its treatments. The NCI recommends small, frequent meals and nutritious snacks throughout the day [2]: five or six small portions without waiting to feel hungry. Make your most complete meal at the time of day when you feel best—for many people, this is breakfast.

The aim is to enrich each bite without making the plate bigger. Add a drizzle of raw extra virgin olive oil to purées and vegetables. Stir powdered milk or grated cheese into creamy soups, and add chopped hard-boiled egg to soups. You can also have ground nuts or add brewer’s yeast. Our menu for people with cancer has practical combinations already planned out.

If you still cannot meet your nutritional needs, discuss this with your medical team so they can assess what support you need [3]. Avoid filling your stomach with clear broths or drinks just before a meal.

How can you prevent weight loss and preserve muscle mass?

Unintentional weight loss during treatment does not mean losing fat alone: you also lose muscle, which can make treatment cycles harder to tolerate and increase tiredness. The European Society for Medical Oncology (ESMO) guideline uses weight loss of more than 5% in six months as one of the diagnostic criteria for cachexia [4]. Cachexia is cancer-related weight and muscle loss. The SEOM and SENPE consensus considers 5% in three months a reliable indicator of nutritional deficit [3]. That is why it is useful to weigh yourself weekly and tell your team promptly.

To slow this decline, the ESPEN guideline estimates energy needs at 25 to 30 kcal per kilogram of body weight per day. The protein reference during treatment is 1.0 to 1.5 g per kilogram per day [1]. In practice, include a protein source at each meal: eggs, fish, poultry, cooked pulses or dairy.

The ESMO guideline also recommends strength exercise two or three times a week, together with moderate aerobic exercise, if your clinical situation allows [4]. Physical activity helps your body use that protein to preserve muscle. Be wary of diets that promise to “starve” the tumour, fasting and carbohydrate restriction. The ESPEN guideline advises against restricting energy if you are malnourished or at risk of malnutrition. It also does not recommend fasting before, during or after chemotherapy: no benefit has been demonstrated, and it increases the risk of malnutrition [1].

What should you eat on chemotherapy day and the days after?

On the day of your session, it helps to arrive with something in your stomach. In consultations we usually suggest a light meal a few hours beforehand. Include easily digested carbohydrates and a little protein: toast with a plain omelette, yoghurt with fine oats, or white rice with chicken. Take water and a snack too, because the session can run long. If your hospital has given you specific instructions, those still come first.

Anti-sickness medicines are chosen according to the vomiting risk of each treatment. The ASCO guideline sets them out to prevent sickness, not just to treat it once it has arrived [5]. That is why it is best to take them at the times you are told, even if you do not feel sick yet. Food goes alongside this medication and does not replace it.

In the days after, many people notice more tiredness, nausea or changes in taste. It helps to have food cooked in advance: soups, purées, croquettes, omelettes or white rice in single portions that heat up in a minute. Note what has agreed with you in each cycle, because that list saves you trying things blindly and helps your team adjust your plan. In the weekly menu for people with cancer you will find a starting point with adaptations for each symptom.

What should you watch in your food if your defences are low?

Some treatments lower neutrophils, a type of white blood cell that fights infection. While they are low, food safety matters more. The so-called neutropenic diet removes fresh fruit, raw vegetables and other foods. A review of six studies with 1,116 people did not find fewer infections than with the usual diet [6]. The authors conclude that it is best to keep to safe food-handling rules [6].

These rules are simple and can be followed at home:

• Wash your hands before cooking and after touching raw meat or eggs.
• Use separate boards and knives for raw and cooked food.
• Cook meat, fish and eggs thoroughly, with no raw parts.
• Wash fruit and vegetables under plenty of water; in our guide to washing fruit and vegetables you will find the step-by-step.
• Choose pasteurised milk, cheese and juices.
• Put leftovers in the fridge within two hours of cooking them and eat them within three days.
• Check the use-by date and do not leave cooked food out of the fridge.

If your team asks you to avoid raw foods for a specific period, for example after a bone marrow transplant, do so. That instruction takes priority over what you read here.

How can you enrich meals when your appetite is low?

When eating is hard, bulk gets in the way. The idea is for each spoonful to carry more energy and protein without the plate growing. Besides adding olive oil raw, there are many ways to enrich food:

• Custard, flan or yoghurt with powdered milk and a spoonful of nut butter.
• Well-set omelette or scrambled eggs with grated cheese or pasteurised fresh cheese.
• Pulse purée with olive oil, which packs a lot into a small volume.
• Homemade shake of milk, ripe banana and fine oats, sipped from a small glass.
• White fish or chicken croquettes or meatballs, bite-sized.
• Soup or cream soup with chopped hard-boiled egg or fine noodles.

Serve on a small plate, change places if the kitchen overwhelms you, and eat with company when you feel like it. A huge portion puts you off before you start.

Pharmacy shakes and oral nutritional supplements have their place when food is not enough. The ASCO cachexia guideline notes that dietary advice, with or without these supplements, increased weight in some trials. The evidence remains limited [7]. Your medical team or dietitian-nutritionist prescribes these supplements and chooses the type and amount. The same guideline states that no appetite-stimulating drug is the standard and that the oncologist decides [7]. Do not take supplements or appetite medicines on your own.

How can you plan the day’s menu when several symptoms come together?

Symptoms rarely come one at a time. You may have mouth sores and a metallic taste at once, or nausea in the morning and some hunger in the afternoon. It helps to organise the day by time slots and textures rather than by fixed dishes.

Use the time of day when you feel best for your most complete meal. For many people that is the morning: egg, yoghurt or cottage cheese with soft bread and cooked fruit. For the rest of the day, keep to small portions of whatever appeals, without waiting until you are hungry.

With mouth sores, go down a step in texture when needed: from tender pieces to a coarse blend, and from there to a smooth purée. When it improves, go back up. If you also cough or notice that you choke on food, it may be dysphagia; see our guide to dysphagia and talk to your doctor.

If the metallic taste puts you off meat, replace it with egg, fish, cheese or tofu, and serve dishes lukewarm or cold. Citrus fruit stings in a mouth with sores because of its acidity. What the evidence says about citrus and cancer is summarised in citrus fruit and cancer.

What about miracle diets, fasting and antioxidant supplements?

Plans circulate that promise to “starve” the tumour or treat it with juices, a single food or prolonged fasts. None has been shown to treat a cancer. Those that cut food heavily wear down muscle just when you need it most, and ESPEN advises against restricting energy if there is malnutrition or a risk of it [1]. If you are wondering about intermittent fasting, we have a guide on what the evidence says; during cancer treatment, the ESPEN guideline does not recommend fasting [1].

With antioxidant supplements, such as vitamins A, C and E, carotenoids or coenzyme Q10, the idea of “protecting” sounds reasonable. A study of 1,134 people with breast cancer on chemotherapy associated taking them before and during treatment with a higher risk of recurrence. The difference did not reach statistical significance [8]. The same study observed a worse outcome with vitamin B12 and with iron supplements [8]. An observational study does not prove cause, but it is enough reason to check first. This refers to supplements, not to the fruit and vegetables on your plate.

Herbal products, concentrated extracts and megadoses can interact with chemotherapy or with supportive medicines. This has been described with St John’s wort. There is less evidence on concentrated extracts of other plants, such as turmeric or green tea capsules. Before taking any, show the packaging to your oncologist or hospital pharmacist. If your team finds a real deficiency, they prescribe the supplement; in vitamin and mineral supplements we explain when they are needed in general.

What questions do we see in consultations?

Three questions come up again and again. The first is whether eating “badly” for a few days ruins the treatment. What counts is arriving at each cycle with strength, and a day of custard, purées and toast can meet that goal. The second is guilt about not feeling hungry: treatment switches appetite off, and it has nothing to do with your willpower.

The third appears at home. Family members insist that you eat more or bring remedies they have read about online. It helps to give them a concrete task: cooking what you do feel like, doing the shopping or preparing small portions to freeze. And to ask them to bring their questions to the consultation, where we review them with your team. If individual support would help, you can consider it with us below.

Frequently asked questions

Does sugar feed the tumour?

Every cell in the body uses glucose, healthy ones too. Cutting sugar out of your diet does not stop a tumour, and if there is a risk of malnutrition ESPEN advises against restricting energy [1]. If you have diabetes or treatment raises your glucose, your team adjusts your plan.

Does a green juice or a shake that promises to cleanse the body work as a meal?

They provide little protein and little energy for what your body needs now. If you fancy them, have them as an extra and not instead of a meal.

How often should I weigh myself?

Once a week, at the same time and on the same scales. Tell your team if you lose weight without trying; the specific warning signs are at the end of this guide.

Does this guide replace my oncologist?

No. It is general information to accompany treatment. Your oncologist and your hospital know your case, and their instructions always come first.