Eating During Chemotherapy: What to Eat, What to Avoid and Myths

During chemotherapy, the main job of nutrition is to get enough protein and energy so you don’t lose weight and muscle. There is no special “anti-cancer” diet, and strict restrictions — on sugar, meat or food in general — more often do harm than good. If you can’t eat enough, medical nutrition is available, and it’s worth discussing with your doctor in good time.

Below I’ll explain what the clinical guidelines are based on, which food safety rules matter when your white blood cell count is low, and why popular myths aren’t worth believing.

Why nutrition matters so much during chemotherapy

Chemotherapy often reduces appetite, changes how food tastes, and causes nausea, inflammation of the mucous membranes and diarrhea. As a result, people eat less than they need and start losing weight — and they lose not only fat but muscle.

Poor nutrition makes treatment harder to tolerate and slows recovery. That’s why both Russian and European guidelines recommend assessing nutrition and weight regularly, from the very start of treatment — not once the patient has already lost a noticeable amount of weight.

How much protein and energy you need

The 2022 practical guidelines on nutritional support from the Russian Society of Clinical Oncology (RUSSCO) give these targets when needs haven’t been measured individually:

• energy — 25–30 kcal per kilogram of body weight per day;
• protein — at least 1.2 g per kilogram of body weight per day, ideally 1.5 g/kg.

The European Society for Clinical Nutrition and Metabolism (ESPEN), in its 2021 guidelines, gives similar figures: energy roughly the same as for a healthy person, 25–30 kcal/kg per day, and protein from 1 to 1.5 g/kg per day.

These are targets, not an exact requirement for you. With kidney or liver disease, obesity or severe wasting, the calculation changes, and it should be done by a doctor or dietitian.

Practical tips that usually help:

• eat little and often if large portions don’t go down;
• start with the protein part of the plate: meat, fish, poultry, eggs, cottage cheese, cheese, beans and lentils;
• add calories without adding volume: butter, cream, nuts and nut butters, if there are no restrictions;
• keep easy snacks within reach: yogurt, soft cheese snacks, kefir;
• drink between meals rather than with them, so liquid doesn’t take up room in your stomach.

If nausea is getting in the way, it needs to be treated first — there’s a separate article on that, “Nausea and vomiting during chemotherapy”.

When medical nutrition and sip feeds are needed

Sip feeding means drinking special medical nutrition drinks in small sips, usually 50–100 ml per hour. These drinks are concentrated in protein and calories and help make up what you can’t manage with ordinary food. ESPEN sees them as the next step after nutritional counseling and treating the symptoms that make eating difficult. RUSSCO recommends additional medical nutrition if ordinary food doesn’t cover your needs.

The RUSSCO guidelines list situations in which patients on chemotherapy and radiotherapy should receive nutritional support:

If even one of these applies to you, it’s a reason to discuss medical nutrition with your doctor. If eating by mouth isn’t possible, the guidelines provide for tube (enteral) feeding, and if that isn’t possible either, intravenous (parenteral) nutrition. These decisions are made only by a doctor.

Weigh yourself regularly and write down the result. Weight loss that’s noticed late is one of the most common — and most preventable — problems during chemotherapy.

Food safety with neutropenia

Neutropenia is a drop in neutrophils, the blood cells that protect against bacteria. With neutropenia, even an ordinary gut infection can be severe. I explained how to read your blood counts in my article “Blood tests before a chemotherapy cycle”.

In the past, patients with low white blood cell counts were put on a strict “neutropenic diet” — no fresh fruit or vegetables. Today many cancer centers, such as Memorial Sloan Kettering Cancer Center (MSK), have moved away from it and focus on hygiene in preparing and storing food:

• don’t eat raw or undercooked meat, fish or eggs (including homemade mayonnaise, sushi, tartare);
• avoid unpasteurized milk, cheeses made from it, unpasteurized juices and honey;
• eat sausages and deli meats only when thoroughly heated;
• wash fruit and vegetables under warm running water, even ones you’ll peel;
• put leftovers in the fridge within two hours, eat them within 48 hours and reheat them only once;
• avoid buffets, salad bars and food that has been left out uncovered for a long time.

Myths that get in the way of treatment

“Sugar feeds the tumor.” Glucose is the main fuel for all the cells in the body, not just tumor cells. As Cancer Research UK explains, you can’t “switch off” sugar for the tumor while leaving it for healthy cells. There’s no evidence that a sugar-free diet helps treatment. Limiting sweets makes sense if you have diabetes or for other medical reasons, but not to “starve the tumor”.

“Fasting helps you get through chemo.” ESPEN recommends not restricting energy in cancer patients, especially those who are losing weight. Cancer Research UK warns that strict diets during treatment can slow recovery and can even be life-threatening. If you’re taking part in a clinical trial with a special eating plan, that’s a different matter — it’s supervised by doctors.

“Baking soda and an alkaline diet make the body alkaline.” The body keeps the acidity of the blood within narrow limits on its own, and food doesn’t change it. Taking baking soda by mouth doesn’t treat cancer, and in large amounts it can cause harm.

“Supplements and antioxidants will strengthen the body.” The RUSSCO guidelines state that high doses of vitamins and minerals without a proven deficiency aren’t justified. If there is a deficiency, it’s corrected based on test results and your doctor’s prescription.

“Herbs are natural and safe.” Herbal remedies are actually the most dangerous because of interactions:

• St John’s wort speeds up the liver enzymes that break down many drugs. In a study published in 2002 in the Journal of the National Cancer Institute, St John’s wort lowered blood levels of the active form of irinotecan by 42%. The authors concluded that patients on irinotecan should stop taking St John’s wort.
• Grapefruit contains substances (furanocoumarins) that irreversibly block the CYP3A4 enzyme in the gut. Because of this, levels of some drugs taken as tablets, including some targeted drugs (for example, nilotinib and sunitinib), can rise. A single glass of juice may be enough to have an effect. Seville (bitter) oranges, pomelos and limes act in a similar way; ordinary oranges don’t.

Bring your oncologist a list of everything you take: medicines, vitamins, teas, tinctures. This is one case where there’s no such thing as too much information.

When to call your doctor

Contact your doctor soon if:

• you can hardly eat or drink;
• vomiting or diarrhea won’t stop despite the medicines you’ve been prescribed;
• you have signs of dehydration: passing little urine, dark urine, dizziness when you stand up, a very dry mouth;
• your weight keeps dropping despite all your efforts;
• pain in your mouth or when swallowing makes it hard to eat.

A raised temperature during chemotherapy is a reason to call your doctor immediately, and if you have chills, weakness or shortness of breath, call your local emergency number (911 in the US, 999 in the UK, 112 in the EU). More in my article “Fever during chemotherapy”.

If you’re having treatment and want to work out how to eat with your regimen, test results and side effects in mind, we can discuss it in a consultation.

Questions to ask your doctor

• Do I need to follow any special eating rules with my treatment regimen?
• Do any of my drugs interact with grapefruit or herbal remedies?
• What weight should worry me, and when should I start medical nutrition?
• How often should my total protein and albumin be checked?
• Can I keep taking my vitamins and supplements?

Sources

1. Practical guidelines on nutritional support for cancer patients — Russian Society of Clinical Oncology (RUSSCO), Malignant Tumors journal, 2022
2. ESPEN Guidelines on Clinical Nutrition in Cancer (a review of the guidelines by Muscaritoli M. et al., Clinical Nutrition) — ESPEN / Society on Sarcopenia, Cachexia and Wasting Disorders, 2021
3. Sugar and cancer — what you need to know — Cancer Research UK, 2023
4. What is the neutropenic diet? — Memorial Sloan Kettering Cancer Center
5. Grapefruit–medication interactions: Forbidden fruit or avoidable consequences? — Canadian Medical Association Journal, 2013
6. Effects of St. John's wort on irinotecan metabolism — Journal of the National Cancer Institute, 2002