Incretin pathways and body composition research

Incretin biology moved from mechanism to medicine faster than most areas of metabolic research. GLP-1 receptor agonism reduces appetite and slows gastric emptying; adding GIP receptor agonism changes adipose and insulin signalling; adding glucagon receptor agonism increases energy expenditure. Retatrutide is a triple agonist at the GLP-1, GIP and glucagon receptors. Unlike most compounds discussed in longevity contexts, it has been evaluated in randomised, placebo-controlled human trials with substantial reported changes in body weight over months, alongside a gastrointestinal side-effect profile consistent with the class. Body composition is not the same as lifespan, and metabolic improvement is a plausible but unproven route to healthspan. Still, this is the part of the field where the evidence tier is genuinely clinical.