Fasting interventions, which involve alternating periods of fasting and refeeding, are generally thought to improve health. But these interventions don’t work as well in old animals. The question is: Why? By studying the short-lived killifish, researchers have shown that older fish deviate from a youthful fasting and refeeding cycle, and instead enter a state of perpetual fasting, even when ingesting food. However, the benefits of refeeding after fasting in old killifish can be restored by genetically activating a specific subunit of AMP kinase, an important sensor of cellular energy. These mutant fish experienced improved health and longevity, indicating that both fasting and refeeding are needed to confer health benefits and act through AMP kinase to do so.
