Eating during cancer treatment: what really helps

Why nutrition matters so much

Up to 70% of people with cancer become malnourished at some point, and this is even more common with gastrointestinal tumors. Malnutrition leaves the body weaker to face treatment: it increases side effects, slows recovery and can worsen outcomes.

The most treacherous part is muscle loss. It can happen silently, even in people who don't visibly lose weight or who are overweight. That is why, during treatment, the priority is to maintain your weight and strength, not to lose weight.

Watch out for weight loss

Tell your team if you unintentionally lose more than:

It is also worth telling your team if your appetite has dropped a lot, if you are eating less than half of what you used to, or if you feel you are losing strength.

Protein at every meal

Protein is what protects your muscles. Include a source at every meal, snacks included: eggs, meat, chicken, fish, milk, yogurt, cheese, beans, lentils and chickpeas. When food alone isn't enough, your team may recommend a nutritional supplement, ideally combined with exercise.

Tips for the most common symptoms

• Nausea: eat small meals several times a day, in a well-ventilated place away from cooking smells. Cold, dry or citrusy foods and ginger often help. Drink fluids between meals, not with them.
• Poor appetite and feeling full quickly: eat a little at a time, every two or three hours, favoring the most nourishing foods. Don't wait until you feel hungry.
• Mouth sores: choose soft foods that are cold or at room temperature. Avoid foods that are very hot, acidic, spicy, hard or dry. Take extra care with mouth hygiene after eating.
• Dry mouth: take small sips of water throughout the day, choose moist foods and dishes with sauces, and use sugar-free candies or gum.
• Changes in taste: a metallic taste improves with olive oil, lemon or honey. Herbs, natural seasonings and colorful dishes make food more appealing. Eat whatever tastes best to you that day.
• Diarrhea: drink plenty of fluids, such as water, coconut water and teas. Eat small meals and avoid fat, milk and foods that cause gas. Peeled apple, banana and tapioca usually help. Severe diarrhea should be reported the same day.
• Constipation: fruit, vegetables, plenty of water and movement.

Food safety

When your defenses are low, food hygiene becomes more important: wash your hands and food well, cook meat and eggs thoroughly, choose pasteurized milk and cheese, drink filtered water and avoid food from questionable sources.

Myths that can get in the way

• "There is a diet that cures cancer." There isn't. Ketogenic, alkaline, fasting or very restrictive diets are not recommended during treatment and can make you lose weight and muscle. Food does not change the pH of your blood.
• "Natural means harmless." Concentrated teas, herbs and herbal medicines can interfere with chemotherapy, making it weaker or more toxic. Tell your team about everything you take.
• "Extra vitamins help." In some studies, high doses of vitamins and antioxidants during chemotherapy were linked to the disease coming back more often. Take only the supplements your team recommends, ideally based on test results.
• "Vitamin drips boost immunity." The injectable vitamin and mineral protocols sold to cancer patients have no scientific basis.
• Probiotic capsules are not recommended when your defenses are low, because of the risk of infection.
• "Sugar feeds the tumor." I explain this myth in another article.

After treatment

Once treatment is over, it is worth adopting the habits that lower cancer risk: plenty of vegetables, fruit and whole grains, little red meat and almost no processed meat, fewer ultra-processed foods and sugary drinks, no alcohol, a healthy weight and physical activity. Read also about obesity and cancer.

Ask to be assessed by a dietitian right at the start of treatment. Ideally, this should happen in the first few weeks after diagnosis, before weight loss begins.

For information only. Your dietitian's and care team's advice takes priority.