The Metabolic Transition Between Fasting And Feeding Alters Aging-Associated Metabolites, Lowers Bcaas, And Stimulates Fgf21 Production In Humans
Many people are exploring fasting as a way to potentially extend their lifespan and improve health. While much research focuses on what happens during the fasting period itself, a recent study shed light on the equally important phase that follows: refeeding. This research investigated how the body’s metabolism changes when people transition from a prolonged fast back to eating.
The study involved adults who underwent a medically supervised fast, followed by a period of eating a plant-based diet. During the fasting phase, the body’s energy use slowed down, and certain “metabolites” — substances made or used when the body breaks down food, drugs, or chemicals — linked to aging, like glucose and specific acids, shifted. Interestingly, levels of branched-chain amino acids (BCAAs), which are essential building blocks for proteins found in foods, remained steady during fasting, likely because the body was releasing them from tissues to maintain energy.
The most notable changes occurred during refeeding. When participants started eating again, a large majority of their metabolite levels returned to normal. However, BCAAs saw a dramatic drop, which is consistent with the body using them up quickly, likely stimulated by insulin. Simultaneously, the hormone FGF21 (Fibroblast Growth Factor 21), a key regulator of metabolism that influences sugar and fat use, increased significantly — by as much as fivefold. This increase in FGF21 was inversely related to the decrease in BCAAs.
These findings suggest that the refeeding period is a crucial window for influencing metabolic markers tied to aging. It highlights that the body’s response to food after a fast is just as vital as the fast itself, potentially offering new insights into how diet impacts healthy aging.