Glossary term

Lean mass

Also known as Lean body mass - Fat-free mass

Everything that isn't fat - muscle, bone, organs. Losing it is the worst possible GLP-1 outcome.

Lean body mass is total body weight minus fat mass. It drives resting metabolic rate (a 10-lb lean-mass gain adds roughly 50 kcal/day of burn), functional strength, fall prevention after 60, and long-term glucose disposal. On GLP-1 protocols without protein and training, lean mass accounts for 25-40% of total weight lost - exactly the outcome you don't want. Defense strategy: 0.7-1.0 g protein per lb of goal lean mass daily, 2-4 resistance sessions a week, 3-5 g creatine daily. Measure with DEXA or a Bod Pod, not bathroom scales.

Medically reviewed byDr. Lena Okafor, MD

Medical Director - updated April 2026 - How we review