Lean mass

Lean mass (or lean body mass) is total body weight minus fat mass — it includes muscle, bone, organs, and water. On GLP-1 medications, a meaningful share of total weight lost (often cited around 25-40%) can come from lean mass rather than fat, which is why preserving muscle through protein intake and resistance training is a common focus of care. See our guides on strength training and protein, fat, and carbohydrates.