The Science on Fasting During Chemo

A growing body of research suggests that fasting—both intermittent and prolonged—may do more than support metabolic health. A 2022 review in Cancer Treatment and Research Communications explores how fasting protocols could enhance chemotherapy’s effectiveness while reducing side effects. Though it may sound unconventional, the science behind it is grounded in well-known cancer biology.

The review highlights that short-term fasting (typically 36 to 72 hours) around chemotherapy may lessen fatigue, nausea, and DNA damage in healthy cells. At the same time, fasting appears to make cancer cells more vulnerable to treatment. This is likely due to fasting’s ability to create a low-glucose, low-insulin, and low-IGF-1 environment—conditions healthy cells can adapt to, but cancer cells cannot.

Fasting works through several mechanisms. First is metabolic selectivity: cancer cells depend heavily on glucose and are metabolically rigid, while healthy cells can switch to alternative fuel sources like ketones during fasting. This creates a “metabolic trap,” where cancer cells are stressed while normal cells are spared.

Second, fasting activates protective pathways in healthy cells—such as autophagy and reduced growth signaling—making them more resistant to chemotherapy. Cancer cells don’t enter this protective state and remain highly sensitive to damage, a phenomenon known as “differential stress resistance.”

Third, fasting may help the immune system. Preliminary studies suggest fasting modulates immune cell activity and could enhance the effectiveness of immunotherapy.

Though early, clinical studies support these findings. Small trials in patients with breast, ovarian, and other cancers show fasting is generally well-tolerated and may improve quality of life. Most benefits are seen with at least 48 hours of fasting, using either water-only fasts or low-calorie, fasting-mimicking diets.While not suitable for everyone, fasting offers a promising, low-cost way to potentially improve cancer treatment outcomes. It’s a compelling area where nutrition, metabolism, and oncology intersect.

de Groot, S., Pijl, H., van der Hoeven, J. J. M., & Kroep, J. R. (2022). Fasting mimicking diets in oncology: Current evidence and future directions. Cancer Treatment and Research Communications, 30, 100526. https://doi.org/10.1016/j.ctarc.2022.100526

By Dr. Sydney Moffat, ND and Dr. Gurdev Parmar, ND, FABNO(USA)