The main idea: do not lose weight or muscle
During chemotherapy the body needs more protein and energy than usual to repair tissues and tolerate the cycles. People who keep their weight and strength complete more treatment, with fewer dose reductions and fewer admissions. So the first question is not "what should I avoid" but "how do I manage to eat enough".
- Weigh yourself once a week. A loss of more than 5 % in a month or two is a reason to speak up and ask for an assessment by a dietitian (many hospitals have an oncology nutrition unit; if not, ask for a referral).
- Protein at every meal: eggs, fish, chicken, pulses, dairy, tofu, nuts. As a general guide, more protein is recommended than in a normal diet; your dietitian will tell you how much in your case.
- 5-6 small meals are better than three large ones. Make the most of the times of day when your appetite is best (usually the morning).
- If you cannot manage with ordinary food, high-protein shakes (from the pharmacy, funded on prescription in Spain when you meet the criteria) are a tool, not a failure.
- Exercise (walking, some strength work) preserves muscle as much as food does. They go together.
Eating according to the symptom
| If you have… | What may help | Avoid |
|---|---|---|
| Nausea | Cold or lukewarm food (less smell), dry foods (toast, crackers) on getting up, ginger, small portions, drinking between rather than during meals. Taking prescribed anti-sickness drugs before nausea starts. | Fried and fatty food, strong smells, long fasting (it makes nausea worse). |
| Mouth sores (mucositis) | Soft, lukewarm textures: purées, soups, yoghurt, eggs, fish; rinses with water and bicarbonate; a straw. | Acidic food (citrus, tomato), spicy, very salty, hard or crunchy food, alcohol, alcohol-based mouthwashes. |
| Diarrhoea | Rice, pasta, potato, banana, stewed apple, carrot, chicken, fish, toast; oral rehydration solution; yoghurt. | Dairy (except yoghurt), raw fibre, pulses, coffee, alcohol, sweets, sweeteners. |
| Constipation (common with anti-sickness drugs and opioids) | Water, fruit with skin, vegetables, pulses, wholegrains, kiwi, prunes, olive oil, walking. | White rice, banana, sitting all day. If it does not ease within 3 days, ask for a prescribed laxative. |
| Metallic taste | Plastic or bamboo cutlery, marinating meat, spices, mint, cold food. | Red meat if it tastes wrong (swap for eggs, pulses, fish). |
| Cold sensitivity (oxaliplatin) | Everything at room temperature for the first 5 days of the cycle. | Ice cream, cold drinks, ice. |
Food safety when your white cells are low
On neutropenic days (your team will tell you when) you do not need a "sterile diet", but you do need extra common sense: wash fruit and vegetables well, cook meat and fish thoroughly, cooked eggs only (no home-made mayonnaise or tiramisu), pasteurised dairy, avoid raw-milk cheeses, uncooked cured meats, sprouted seeds, sushi and raw shellfish. Be careful with buffets and food left out of the fridge for hours.
Supplements, herbs and "natural remedies"
Always check before taking anything, even if it is "natural". Examples of real interactions:
- St John's wort: lowers the levels of irinotecan and many other drugs. Not allowed during treatment.
- High-dose turmeric, concentrated green tea, garlic capsules, ginkgo: can alter clotting or drug metabolism.
- High-dose antioxidants (megadoses of vitamin C, E, beta-carotene): could interfere with chemotherapy and radiotherapy; not recommended.
- Grapefruit: interferes with several oral drugs. Best avoided if you take tablets.
- Vitamin D if you are deficient, and folic acid only if your doctor advises it (note: it interacts with 5-FU/capecitabine at high doses).
None of this means herbal medicine is "bad": it means your oncologist needs to know what you take in order to avoid a problem.
Alcohol
The most prudent course is to avoid it during treatment: it irritates the gut lining, dehydrates, worsens nausea and neuropathy and burdens the liver. An occasional drink on a good day, away from chemotherapy days, is usually acceptable; ask.
Myths that do harm
- "Sugar feeds the tumour": all cells use glucose; cutting out carbohydrates does not "starve" the cancer, but it does make you lose weight and muscle. The sensible approach is to reduce added sugars and ultra-processed foods, not to eliminate carbohydrates.
- Fasting and ketogenic diets during chemotherapy: under study, without sufficient evidence, and with a real risk of malnutrition. Only within a trial and with supervision.
- Alkaline diet: food does not change the pH of your blood. No scientific basis.
- "If I eat red meat the cancer will come back": high intake of red and processed meat is linked to a higher risk of colorectal cancer in the general population; during treatment the priority is enough protein, whatever the source. Afterwards, a Mediterranean-style diet rich in fibre and low in processed meat is the reasonable recommendation for the future.
What to ask at your appointment
- Can I see a hospital dietitian?
- How much weight have I lost since diagnosis, and at what point should I worry?
- Am I entitled to nutritional supplements on prescription?
- I take these supplements or herbs (list): should I stop any of them?
- On which days of the cycle are my white cells low, when I should be strictest about food safety?
