This systematic review, published today in Annals of Internal Medicine, examined body composition changes from incretin-based therapies (liraglutide, semaglutide, tirzepatide, dulaglutide) across 36 randomized controlled trials in adults with obesity. While these medications consistently reduced total fat mass and visceral adiposity, muscle-related losses exceeded expected benchmarks in roughly two-thirds of incretin-treated groups — and notably, in half of lifestyle/placebo comparator groups that also lost weight. No studies measured objective physical function outcomes.