Is lean mass the same as muscle?
No. Lean mass, as measured in trials, includes muscle but also water, organs and other non-fat tissue. So “lean-mass loss” and “muscle loss” are related but not the same. Bone is measured separately.
The Wegovy® and Zepbound® labels both state, in their pharmacology sections, that the medicine lowers body weight with greater fat-mass loss than lean-mass loss.[1][2]
What does the research suggest?
A 2024 review in Diabetes, Obesity and Metabolism (Neeland, Linge and Birkenfeld) found that reported lean-mass changes with GLP-1-based therapies vary between studies, and reviews the ways to limit loss that are in use or in development — chiefly exercise and nutrition.[3]
The 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society lists preserving muscle and bone through resistance training and an appropriate diet among its priorities, along with assessing muscle strength and body composition at the start.[4] The WHO recommends muscle-strengthening activity on 2 or more days a week for adults in general.[5]
Why is there no protein target on this page?
Protein needs depend on body size, kidney function, other conditions and the rest of your diet. The advisory leaves the number to individual assessment by a clinician or dietitian,[4] and so does PepLabo.
What does PepLabo not do?
PepLabo does not measure muscle, and neither can any phone app on its own — that takes a body-composition scan or a strength test. It records what you do (workouts, protein) and what you can see (weight, photos), so your clinician has something to read.
Wegovy® and Ozempic® are registered trademarks of Novo Nordisk A/S; Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. They are named only to identify the medicines and their labels. PepLabo has no affiliation with these companies.
