By Dr. Stephen Phinney and the Virta Team
Intermittent fasting (ie, short periods of restricted intake or no calorie intake) has received a lot of attention recently. However intermittent breaks in adherence to ketogenic diets has not been studied carefully in humans. There was a recent longevity study in mice fed a ketogenic diet every other week for a few years (Newman 2017) in which the mice had better function in middle age but didn’t live any longer. In a similar study where the mice were continuously in ketosis (Roberts 2017), they remained youthful and lived 13% longer.
In our clinical experience with human patients, however, we typically find that more than a few days of ‘falling off course’ can reverse keto-adaptation and take from several days to up to a week or more to fully recover. The timeline for this likely depends on one's level of insulin resistance and the amounts of carbohydrate consumed.
Here are what can be expected when a person consumes enough carbohydrates to reverse the keto-adapted state:
Newman JC, Covarrubias AJ, Zhao M, Yu X, Gut P, Ng CP, Huang Y, Haldar S, Verdin E. Ketogenic Diet Reduces Midlife Mortality and Improves Memory in Aging Mice. Cell Metab. 2017; 26:547-557.
Roberts MN, Wallace MA, Tomilov AA, Zhou Z, Marcotte GR, Tran D, Perez G, Gutierrez-Casado E, Koike S, Knotts TA, Imai DM, Griffey SM, Kim K, Hagopian K, Haj FG, Baar K, Cortopassi GA, Ramsey JJ, Lopez-Dominguez JA. A Ketogenic Diet Extends Longevity and Healthspan in Adult Mice. Cell Metab. 2017; 26:539-546.