Research paper
Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG 3rd, Leeuwenburgh C, Mattson MP. Flipping the metabolic switch: understanding and applying the health benefits of fasting. Obesity (Silver Spring). 2018;26(2):254-268.
Why we cite it
Defines and explains the "metabolic switch" — the physiological transition from glucose to fatty acid and ketone metabolism — and argues it is the mechanism underlying the health benefits of intermittent fasting. This is a review, so the framing is the authors' synthesis rather than a result established here. It states that the switch "typically occurs between 12 to 36 hours after cessation of food consumption depending on the liver glycogen content at the beginning of the fast, and on the amount of the individual's energy expenditure/exercise during the fast" — both conditions are the paper's own and both were missing from this record until 2026-09-02. The review further argues that benefits come from both the fasting state and the repeated switching itself. This is the primary source for the project's treatment of the metabolic switch concept, used across companions covering glycogen depletion, ketone production, fasting windows, hunger waves, and fatty acid oxidation.