From the Guidelines
Fasting during chemotherapy is not recommended without medical supervision due to the risk of malnutrition and potential harm, although some research suggests potential benefits of short-term fasting in improving treatment efficacy and tolerability. Patients should always consult their oncologist before attempting any fasting regimen while undergoing cancer treatment 1. The ESPEN guidelines on nutrition in cancer patients recommend against using dietary provisions that restrict energy intake in patients with or at risk of malnutrition, citing the risk of malnutrition and potential harm 1.
Some studies suggest that short-term fasting (typically 24-72 hours before and/or after chemotherapy sessions) may have potential benefits, including protecting normal cells and making cancer cells more vulnerable to treatment 1. However, maintaining adequate nutrition is crucial during cancer treatment, as many patients already struggle with weight loss, muscle wasting, and malnutrition 1. For patients interested in exploring fasting, modified approaches like the fasting-mimicking diet might be safer alternatives, providing low calories (around 800-1100 calories daily) with low protein and carbohydrates but adequate fats for 3-5 days around treatment.
Key considerations for patients undergoing chemotherapy include:
- Maintaining adequate nutrition to prevent malnutrition and weight loss
- Avoiding restrictive diets that may exacerbate malnutrition
- Considering modified fasting approaches under medical supervision
- Monitoring for potential side effects of fasting, such as excessive weight loss and malnutrition
- Patients with diabetes, significant weight loss, or other metabolic conditions should be particularly cautious about fasting during treatment 1.
In terms of nutritional assessment and counseling, patients should be referred to a dietitian to design an appropriate nutritional therapy based on their health condition and individual needs 1. Regular monitoring of nutritional status and body composition is essential to prevent malnutrition and related complications 1.
From the Research
Role of Fasting in Chemotherapy
- Fasting has been shown to induce cellular protection and chemotherapy resistance in patients undergoing chemotherapy 2, 3, 4.
- The protective effect of fasting is mediated by a reduction in glucose and insulin-like growth factor 1 (IGF-I) levels, which can promote the differential protection of normal and cancer cells 2.
- Preliminary reports indicate that fasting for up to 5 days followed by a normal diet may protect patients against chemotherapy without causing chronic weight loss 2.
- Intermittent fasting has been shown to enhance treatment with both chemotherapy and radiation therapy, and reduce certain side effects of cytotoxic therapy 3, 5.
Comparison with Caloric Restriction
- Caloric restriction (CR) has been shown to extend lifespan and reduce age-related diseases, but its effects on cancer treatment are still being studied 3, 4.
- Chronic CR can be challenging to employ in cancer patients, and intermittent fasting or CR mimetic drugs may be more suitable alternatives 3.
- Fasting and CR have different effects on normal and cancer cells, and may reduce certain side effects of cytotoxic therapy 3, 4.
Current Evidence and Future Directions
- Current evidence suggests that intermittent fasting may improve the effectiveness of chemotherapy, decrease treatment-related side effects, and ameliorate treatment-related decreases in quality of life and daily functioning 5.
- Larger controlled trials are needed to better elucidate the effect of intermittent fasting on treatment and patient outcomes during chemotherapy 5, 6.
- The effects of intermittent fasting on human cancer incidence and prognosis remain unknown due to a lack of high-quality randomized clinical trials 6.