A model of the systemic metabolic effects of the mitochondrial-derived peptide hormone MOTS-c. Exercise, diet (pro-longevity dietary interventions), and aging may affect the production, secretion, and activity of MOTS-c. Skeletal muscle is a major target of circulating MOTS-c, but experimental evidence also points to fat cells as a potential target. Depending on the environment, MOTS-c may have dual roles as an anabolic and a lipolytic hormone.