People who’ve never fasted typically experience very mild and brief periods of discomfort, ranging from gnawing hunger to headaches, irritation, and low energy. Dr. David Perlmutter, author of ‘Brain Maker’: “Fasting is baked into our evolution and our physiology and it can yield benefits to our brains and bodies, at a biochemical level, that we’re only just beginning to understand.”

Dr. Peter Osborne, author of ‘No Grain, No Pain’: “It’s of the cheapest and easiest health tools you can access. Fasting has been shown to be beneficial for a variety of different diseases and health problems including rheumatic diseases, chronic pain syndromes, hypertension, and metabolic syndrome, obesity, cancer, digestive disorders, and more.

Dr. Rhonda Patrick, PhD health researcher: “Most people who practice fasting report feeling energized and more alert at the end of their fast, which may represent a “resetting” of their body’s natural metabolic rhythms.”