Fasting and adopting plant based diets
Fasting. Healthy breakfast, diet food concept. Organic meal. Fat loss concept.
For centuries, noted by the Father of Medicine, Hippocrates of Kos, Greece, physicians noticed that people who fell ill often stopped eating. What was once viewed as an unwelcome part of sickness may in fact be a biological defense. Modern research, including work highlighted by Dr. Michael Greger, suggests that short-term fasting can momentarily sharpen immune function rather than weaken it. (Nutritionfacts.org)
In early experiments, scientists observed that the blood of fasting mice became dramatically more effective at fighting infection nearly an eightfold increase in the ability of white blood cells to destroy invading bacteria. Human studies offer similar clues. Volunteers placed on a very low-calorie fasting regimen for two weeks showed stronger immune responses and a 24% increase in natural killer cell activity, the same cells responsible for destroying abnormal or cancerous cells. (Nutritionfacts.org)
These findings have fueled interest in fasting as a way to support the body’s surveillance system against cancer. Yet, fasting has long been discouraged in oncology because of cachexia, the dangerous wasting syndrome that affects many cancer patients. Tumors, hungry for energy and protein, can redirect the body’s metabolism to feed their growth. Simply increasing calorie intake rarely reverses this process, raising the question of whether loss of appetite during cancer might, for some patients, be a protective adaptation rather than a harmful one. (Nutritionfacts.org)
The most intriguing data involve fasting around chemotherapy. Traditional chemotherapy damages both cancer cells and healthy cells. Short-term fasting appears to shift healthy cells into a “maintenance” mode, making them more resistant to treatment-related injury, while cancer cells, with their relentless drive to divide, cannot adapt as easily. Early animal studies even showed that fasting alone could slow tumor growth and, when combined with radiation, amplify anti-tumor effects. (BMC Cancer)
Human trials remain small, but early reports are encouraging. Patients who fasted before chemotherapy described less fatigue, nausea, and digestive discomfort. Some studies noted lower bone-marrow toxicity, while others found mixed results. Importantly, supervised fasting protocols have been shown to be safe for most participants, with rapid weight recovery afterward. (BMC Cancer)
Fasting may also lower IGF-1, a growth-promoting hormone linked to cancer risk. Plant-based diets, naturally lower in protein, can produce a similar reduction, suggesting that dietary patterns and fasting may work synergistically to dampen cancer-friendly signaling pathways. (Cell Reports)
While fasting is not yet a standard cancer therapy, emerging evidence points to a simple idea: temporarily reducing caloric intake may heighten immune strength, soften chemotherapy’s side effects, and help shift the body’s biology into a state less favorable to cancer.
References
Greger, M. “The Effects of Fasting on Cancer.” NutritionFacts.org (2025). (Nutritionfacts.org)
Longo, V. & Mattson, M. “Fasting and cellular stress resistance.” Cell Metabolism (2014).(PUB MED)
Safdie, F. et al. “Fasting and cancer treatment tolerance.” Aging (2009). (NIH)
Levine, M. et al. “Low protein intake and IGF-1 reduction.” Cell Reports (2014). (Cell Reports)
