Lean Mass

Deep dive

Lean Mass: complete reference

Lean mass (also "lean body mass" or "fat-free mass") refers to all body tissue excluding fat — including muscle, bone, organs, fluid, and connective tissue. Skeletal muscle represents the largest component of lean mass and is the most metabolically active tissue, contributing approximately 20% of resting metabolic rate at typical body composition. Lean mass is critical для metabolic health: more lean mass = higher metabolic rate, better glycemic control, lower fall risk in aging, and better functional capacity. During weight loss, both fat and lean mass typically decline — the proportion varies dramatically based on protein intake, exercise (especially resistance training), and rate of loss. GLP-1-induced rapid weight loss is associated with ~25-40% of total weight loss coming from lean tissue without targeted intervention. Preservation strategies: adequate protein (0.7-1g per pound goal weight minimum), resistance training 2-3×/week, gradual rather than aggressive caloric deficit beyond what GLP-1 creates naturally.

In practice

You lose 30 lbs on Wegovy. Without protein/exercise focus, ~10 lbs may be lean mass (muscle). With protein + lifting, you can lose 25+ lbs of fat while preserving most muscle.

Clinical context

Lean mass preservation is the most overlooked aspect of GLP-1 weight loss. Protein + resistance training are evidence-based interventions.