Fasting During Cancer Treatment

Why do people fast?

People may fast for religious, cultural, spiritual or health reasons.

Some people also hear that fasting may "starve cancer cells" or make chemotherapy work better.

Research is being conducted on fasting and fasting-mimicking diets in cancer care, but this is still an area of active research. It should not be assumed that fasting is beneficial or appropriate for every cancer patient. 

Why can fasting be a problem?

Cancer and cancer treatment can already make it difficult to get enough:

Calories

Protein

Fluids

Vitamins and minerals

Prolonged or inappropriate fasting may increase the risk of weakness, dehydration, weight loss and malnutrition.

This can be particularly concerning if you are already losing weight or eating poorly. 

Can I fast for religious reasons?

Possibly—but this should be discussed with your cancer-care team.

The safety of fasting depends on:

Type and stage of cancer

Treatment being received

Weight and nutritional status

Diabetes or other medical conditions

Kidney and liver function

Risk of dehydration

Medicines being taken

What about intermittent fasting?

Do not assume that a popular intermittent-fasting schedule is appropriate during chemotherapy, radiotherapy or other treatment.

If you are interested in fasting, ask your oncologist and dietitian first.

What about Ayurveda?

Ayurvedic traditions include different forms of dietary restriction and fasting.

These should not automatically be applied to a person receiving cancer treatment.

Traditional practice still needs to be adapted to the individual patient's medical condition.

Remember

Fasting is not a proven substitute for cancer treatment.

If you are considering fasting during treatment, discuss it before you start.

Reliable sources: National Cancer Institute (NCI), World Health Organization (WHO), relevant national cancer-care guidelines, and appropriate peer-reviewed evidence.