From the Guidelines
Fasting is not recommended as a treatment for cancer due to the risk of malnutrition and worsening of quality of life. While some studies suggest that short-term fasting may enhance the effectiveness of certain cancer treatments, the current evidence is not strong enough to support its use as a standalone treatment 1. The ESPEN guidelines on nutrition in cancer patients recommend against the use of dietary provisions that restrict energy intake in patients with or at risk of malnutrition, as this can lead to secondary micronutrient deficiency, exacerbation of malnutrition, and high cost 1.
The potential benefits of fasting in cancer treatment are still being studied, and the biological mechanism behind these benefits involves differential stress resistance, where normal cells can better adapt to fasting conditions than cancer cells, potentially making cancer cells more susceptible to treatment 1. However, cancer patients often struggle with maintaining adequate nutrition and preventing weight loss, and fasting could potentially worsen malnutrition and muscle wasting.
Some studies have investigated the use of short-term fasting protocols, such as water-only fasts for 24-72 hours before and/or after chemotherapy treatments, or fasting-mimicking diets that restrict calories while providing essential nutrients 1. However, these studies are limited, and more research is needed to fully understand the effects of fasting on cancer treatment outcomes.
In terms of nutritional support, the evidence suggests that nutritional therapy can improve body weight and energy intake in cancer patients who are malnourished or at risk of malnutrition, but the effect on survival is unclear 1. Nutritional counseling may be beneficial in select patients suffering from poor oral intake and weight loss, and dietary interventions can improve quality of life, particularly in patients receiving radiotherapy 1.
Overall, while fasting may have potential benefits in cancer treatment, the current evidence is not strong enough to support its use as a standalone treatment, and cancer patients should consult with their oncologist and a dietitian specializing in oncology nutrition to develop a safe and effective approach to nutrition and cancer treatment. The priority should be to maintain adequate nutrition and prevent malnutrition, rather than restricting energy intake through fasting.
From the Research
Fasting and Cancer Treatment
- Fasting has been studied as a potential method to improve cancer treatment outcomes, with some studies suggesting it may reduce chemotherapy-related toxicity and tumor growth 2, 3.
- However, the current evidence is limited, and most studies have methodological limitations, such as small sample sizes and heterogeneous protocols 2, 4.
- A systematic review of clinical data on fasting during cancer treatment found that fasting for short periods does not have a beneficial effect on the quality of life of cancer patients during treatment 2.
Motivations for Fasting
- Patients' primary motivation to fast during cancer treatment is to lower the negative side effects of chemotherapy and to gain a sense of control over their treatment 5.
- Fasting is also reported as a coping strategy to reduce anxiety and to adapt to social and lifestyle constraints 5.
Effects of Fasting on Chemotherapy
- Some studies suggest that fasting may improve the efficacy of anticancer treatments without increasing their adverse effects 6, 4.
- A systematic review of the effects of fasting on treatment response of adults undergoing chemotherapy found that fasting of at least 24 hours appears to be safe and may have beneficial effects on chemotherapy toxicity 4.
- However, the evidence is still limited, and well-designed randomized clinical trials are needed to fully understand the effects of fasting on chemotherapy-related adverse events 4.
Recommendations for Future Studies
- Future studies should aim to investigate the effects of fasting on chemotherapy-related adverse events and treatment outcomes in cancer patients 3, 4.
- Studies should be well-designed, with large sample sizes and homogeneous protocols, to provide high-quality evidence on the effects of fasting in cancer treatment 4.