Body composition changes during weight reduction with tirzepatide

Researchers studied adults with obesity, but without diabetes, who received weekly tirzepatide or a placebo for 72 weeks. In a 160-person subgroup, body scans measured fat, lean mass, and belly fat. Tirzepatide reduced body weight by about 21%, fat mass by about 34%, and visceral fat, the fat around internal organs, by about 40%. Lean mass fell by about 11%, but roughly three-quarters of the weight lost came from fat. Lean mass includes muscle, but also water and organs, so the scans cannot show exactly how much muscle was lost.

What this means for you: Tirzepatide weight loss in this study was mostly fat loss, but some lean tissue was lost too. This supports using the medicine only when appropriate and pairing it with enough protein and resistance exercise, rather than buying it solely to preserve muscle; the body-scan subgroup was small and the study was funded by the drug’s maker.