The Complementary Role of Exercise and Fasting in the Treatment of Cancer: A Narrative Review of Mechanisms Related to Metabolic Stress Elements

Background: Complementary methods such as physical activity (PA) and fasting are particularly important for cancer patients. The present study reviewed the effects of regular PA and fasting on cancer patients and attempted to explain the relevant mechanisms. Methods: Several electronic databases such as PubMed, Elsevier, and Google Scholar were searched for keywords. After reviewing, 412 articles were identified until February 1, 2021. The inclusion criteria included meta-analysis, clinical intervention studies that considered different effects of fasting and various types of exercise on health indicators. After carefully reviewing and eliminating duplicates, 68 articles were identified based on the PICO format (participants, intervention, comparison, and results). Results: The short-term fasting (STF) before chemotherapy (48-72 hours) or rehabilitation exercise could be modulating fasting blood sugar, growth factors, oxidative stress (OS), and inflammatory pathways. In addition, physiological metabolic stress induced by STF or rehabilitation exercise could regulate sex hormone-binding globulin, fat oxidation, leptin secretion, hyperinsulinemia, maintaining mass muscle, and bone density, boosting the immune system, and improving the therapeutic index of cancer. Conclusion: Metabolic stress in cancer cells leads to the intake of high doses of chemotherapy. The rehabilitation exercise prevents the complications of the disease and improves the patient’s quality of life. Thus, these interventions can be used to improve the cancer-based therapeutic index on individual differences.