Nutrition in Oncology: Diet for Cancer Prevention and During Treatment

Created: 16.01.2023 · Last Updated: 19.08.2026 · Category: Nutrition and Dietetics · Prepared by the Academic Hospital Web and Editorial Board.

Why Is Nutrition Important in Oncology?

Nutrition, physical activity and body weight are important not only in relation to cancer but also for cardiovascular disease, hypertension and type 2 diabetes.

In oncology, nutrition has two distinct roles:

  • Healthy lifestyle habits intended to help reduce the risk of developing cancer
  • Ensuring adequate energy, protein and nutrient intake in people who are receiving cancer treatment

These two situations are related but should not be treated as identical.

No individual food or diet can guarantee cancer prevention or cure cancer. Current guidance focuses on the overall long-term dietary and lifestyle pattern rather than a single “anti-cancer” food.

Is Nutrition for Cancer Prevention the Same as Nutrition During Treatment?

No.

For generally healthy adults, cancer prevention guidance focuses on maintaining a healthy body weight, eating a diet rich in vegetables, fruit, whole grains and legumes, and remaining physically active.

During active cancer treatment, priorities may change. Cancer itself and treatments such as chemotherapy, radiotherapy and surgery can cause loss of appetite, weight loss, nausea, vomiting, taste changes, mouth sores, swallowing problems and gastrointestinal symptoms.

In these circumstances, maintaining adequate calorie and protein intake may become more important than following a restrictive diet.

How Should You Eat to Reduce Cancer Risk?

A healthy dietary pattern for cancer prevention generally emphasises:

  • A variety of vegetables
  • Fruit, particularly whole fruit
  • Whole grains
  • Legumes
  • Nuts, seeds and other plant foods
  • Appropriate sources of protein such as fish and poultry

Red and processed meats, sugar-sweetened beverages, highly processed foods and refined grain products should be limited.

How Much Physical Activity Is Recommended?

Regular physical activity is associated with a lower risk of several cancers and helps support a healthy body weight.

For adults, general prevention guidance recommends:

  • 150–300 minutes of moderate-intensity activity per week, or
  • 75–150 minutes of vigorous-intensity activity per week, or
  • An appropriate combination of the two.

Reaching or exceeding the upper end of the range may provide additional benefit. Reducing prolonged sedentary time is also important.

Does Body Weight Affect Cancer Risk?

Excess body weight and obesity are associated with an increased risk of several cancers.

Maintaining a healthy weight throughout adult life and avoiding excessive weight gain are therefore important cancer prevention strategies.

However, intentional weight loss is not automatically appropriate for a person who is undergoing cancer treatment and losing weight unintentionally. Nutritional status needs to be assessed separately during active treatment.

Why Are Vegetables, Fruit, Whole Grains and Legumes Important?

Plant foods provide vitamins, minerals, fibre and a variety of bioactive compounds.

Dietary patterns rich in vegetables, fruit, whole grains and legumes can support a healthy body weight and are associated with a lower risk of certain cancers.

High-fibre foods such as whole grains and legumes are particularly relevant in dietary patterns associated with a lower risk of colorectal cancer.

Should Red and Processed Meat Be Limited?

Current cancer prevention guidance recommends limiting red meat and consuming as little processed meat as possible.

Processed meats include products that have been cured, smoked, salted or otherwise processed, such as sausages, salami, ham and similar products.

Protein intake can also come from fish, poultry, legumes and other suitable sources.

Does Alcohol Increase Cancer Risk?

Yes. Alcohol consumption is associated with several types of cancer.

For cancer prevention, the American Cancer Society states that it is best not to drink alcohol.

Can Vitamins or Supplements Prevent Cancer?

Routine use of high-dose vitamin, mineral, antioxidant or herbal supplements is not recommended for cancer prevention.

Whenever possible, nutrients should be obtained through a balanced diet.

People receiving cancer treatment should discuss supplements with their treatment team. Some vitamins, antioxidants and herbal products can interact with cancer medicines or affect treatment.

How Should You Eat During Cancer Treatment?

There is no single diet suitable for every person with cancer.

A nutrition plan should consider:

  • Cancer type and stage
  • Treatment being given
  • Current weight and weight changes
  • Muscle mass
  • Appetite
  • Ability to chew or swallow
  • Digestive symptoms and treatment side effects

People who are losing weight or struggling to eat during treatment may need more calories and protein. Small frequent meals, energy- and protein-dense foods or oral nutrition supplements may be appropriate in selected patients.

Why Are Weight Loss and Malnutrition Important?

Cancer and cancer treatment can reduce food intake and alter the body's energy and protein requirements.

Unintentional weight loss and loss of muscle mass can:

  • Increase weakness
  • Reduce quality of life
  • Make cancer treatments more difficult to tolerate
  • Affect recovery

For this reason, food intake, weight changes and nutritional risk should be assessed throughout cancer care.

Unintentional weight loss during cancer treatment should not be viewed as desirable weight loss. Early nutritional intervention is particularly important when muscle mass is being lost.

How Can Nutrition Be Adjusted for Treatment Side Effects?

Cancer treatment can cause different nutrition-related symptoms in different patients.

Common problems include:

  • Loss of appetite
  • Nausea and vomiting
  • Taste and smell changes
  • Dry mouth or mouth sores
  • Difficulty swallowing
  • Diarrhoea or constipation
  • Early satiety

Nutrition should therefore be adjusted to the symptom rather than using the same diet for every patient.

For example, small frequent meals and energy- and protein-dense foods can help with appetite loss and weight loss, while texture modification may be required in patients with swallowing difficulties.

Nutrition in Oncology Should Be Individualised

Nutritional needs differ between cancer prevention, active treatment and survivorship. Individual assessment is especially important when there is unintentional weight loss, poor appetite or treatment-related difficulty eating.

Frequently Asked Questions

Is there a specific diet that prevents cancer?
No. No single food or diet can guarantee cancer prevention. Maintaining a healthy body weight, being physically active and following a dietary pattern rich in vegetables, fruit, whole grains and legumes can contribute to reducing cancer risk.
Should people with cancer completely avoid sugar?
The fact that cancer cells use glucose does not mean that completely eliminating sugar or carbohydrates treats cancer. Limiting sugar-sweetened drinks and highly processed foods is appropriate for general health, but unnecessary dietary restriction during active treatment can worsen weight and muscle loss.
Is protein important during cancer treatment?
Yes. Protein is important for maintaining muscle mass, tissue repair and nutritional status. Individual protein requirements should be determined according to treatment and nutritional status.
Can people with cancer take vitamin supplements?
Supplements should be used when indicated and discussed with the treatment team. High-dose vitamins, antioxidants and herbal products can potentially interact with some cancer treatments.
Is weight loss during cancer treatment normal?
Unintentional weight loss should not be considered normal or desirable. Loss of muscle mass in particular can negatively affect treatment tolerance and quality of life, and nutritional assessment is recommended.
How much exercise is recommended for cancer prevention?
Adults are generally advised to get 150–300 minutes of moderate-intensity activity or 75–150 minutes of vigorous-intensity activity per week, or an appropriate combination. Exercise during active cancer treatment should be adapted to the person's medical condition.
Does alcohol increase cancer risk?
Yes. Alcohol consumption is associated with several types of cancer. From a cancer-prevention perspective, the lowest-risk approach is not to drink alcohol.
Academic Hospital note: Nutrition for people with cancer should be planned according to cancer type, treatment, weight changes and treatment-related symptoms. Early assessment is particularly important when unintentional weight loss or difficulty eating occurs. You can book an appointment.

References

  1. Academic Hospital. Nutrition in Oncology
  2. American Cancer Society. Guideline for Diet and Physical Activity for Cancer Prevention
  3. American Cancer Society. Nutrition and Physical Activity Guideline for Cancer Survivors
  4. National Cancer Institute. Nutrition During Cancer Treatment
  5. Muscaritoli M, et al. ESPEN Practical Guideline: Clinical Nutrition in Cancer
  6. World Cancer Research Fund. Cancer Prevention Recommendations