Glycogen-depleting endurance exercise performed immediately before a three-day water-only fast does not significantly enhance autophagic flux in peripheral blood mononuclear cells beyond the effect of fasting alone in healthy adults.

When a person fasts for three days, the body stops receiving food, so blood sugar and insulin levels drop. This tells cells to stop growing and start cleaning up damaged parts. A key control switch called mTOR turns off, which triggers a cleanup process that packages and breaks down old or broken cellular material. This cleanup happens in immune cells in the blood, and it happens fully even without prior exercise. Exercise before fasting depletes sugar stores, but that does not make the cleanup any stronger than fasting alone.