Nutrition and Weight Calculator for Cancer Treatment

Why nutrition is part of cancer treatment

Between a fifth and two thirds of people with cancer become malnourished at some point, depending on the cancer type and stage. Losing weight and muscle makes chemotherapy harder to tolerate, delays cycles, slows recovery from surgery and lowers quality of life. Yet weight loss is often shrugged off as an expected side effect.

The European Society for Clinical Nutrition and Metabolism (ESPEN) recommends that everyone with cancer is screened for nutritional risk at diagnosis and regularly during treatment, and that anyone at risk is assessed by a dietitian. This calculator gives you the same first numbers a dietitian would start from.

What the estimates mean

When energy needs are not measured directly, ESPEN suggests assuming 25 to 30 kcal per kilogram of body weight per day for people with cancer. Protein needs rise above the general reference intake of 0.83 g per kg: more than 1 g per kg per day, and up to 1.5 g per kg if it can be achieved, to protect muscle while the body repairs itself.

These are starting points. Fever, wounds, infection, or a very high or low body weight all shift them, and a dietitian may calculate from an adjusted weight rather than your actual weight. After treatment, needs return towards those of the general population, which the recovery and prevention options reflect.

Weight loss that needs a conversation

ESPEN and the GLIM consensus on malnutrition treat losing more than 5 percent of body weight within six months, or more than 2 percent if BMI is already below 20, as significant. Cancer cachexia, a syndrome of ongoing muscle loss driven by the tumour and inflammation, is defined by the same thresholds.

The important point is timing. Nutritional support, from food-first advice and oral supplements to, in some cases, tube feeding, works far better early than after weeks of decline. If your weight change shows red on this page, say so at your next appointment or call your nurse.

BMI in cancer care

BMI was designed to describe populations, not to judge individuals. A person can sit in the healthy range while losing muscle and gaining fat, a pattern common during treatment that CT scans reveal but the scales hide.

During active treatment the aim is a stable weight and preserved strength, whatever the BMI. Deliberate weight loss is usually postponed. After treatment, reaching and keeping a healthy weight lowers the risk of recurrence for several cancers, including breast, bowel and endometrial cancer, and lowers the risk of heart disease and diabetes that many survivors face.

Eating well during treatment

• Eat small amounts often: six mini-meals are easier than three large ones when appetite is poor.
• Put protein in every meal and snack: eggs, dairy, fish, meat, beans, lentils, tofu, nuts.
• Add energy without bulk: olive oil, butter, cream, cheese, nut butters, full-fat yoghurt.
• Keep fluids up, but drink between meals rather than filling up before them.
• Taste changes: try cold foods, sharp or sweet flavours, plastic cutlery if things taste metallic.
• Be wary of restrictive diets. ESPEN advises against diets that cut energy intake in anyone at risk of malnutrition, and there is no evidence that fasting or ketogenic diets improve cancer outcomes.
• Ask about oral nutritional supplements if you cannot meet your needs with food.

After treatment: weight, food and recurrence

The World Cancer Research Fund’s recommendations for survivors mirror those for prevention: keep to a healthy weight, be physically active for at least 150 minutes a week, eat plenty of vegetables, fruit, whole grains and pulses, limit red and processed meat, sugary drinks and alcohol. Resistance exercise twice a week helps rebuild the muscle lost during treatment.

If your weight rose during treatment, as it often does with hormone therapy or steroids, the gentle target on this page keeps you above your resting energy so that weight loss comes from fat rather than muscle.

Questions to ask your team

Bring the result with you and ask:

• Can I see a dietitian who works with cancer patients?
• How much weight have I lost since diagnosis, and does it need action?
• Should I use oral nutritional supplements, and which ones?
• Is it safe for me to exercise, and what kind helps most?
• Are any of my medicines affecting my appetite or weight?