Quick answer
The proportion of fat mass, lean mass (muscle), bone, and water in the body. GLP-1-induced weight loss is roughly 60-75% fat and 25-40% lean mass, similar to other caloric restriction methods.
Full definition
Body composition refers to the breakdown of body mass into compartments — fat mass, lean (skeletal muscle and organ) mass, bone mineral, and water. It is measured via DEXA scan, BIA, hydrostatic weighing, or air displacement plethysmography. With GLP-1-induced weight loss, fat:lean ratio of loss is roughly comparable to other caloric restriction methods (60-75% fat / 25-40% lean), though this remains an active research area. Resistance training and adequate protein intake (1.2-1.6 g/kg/day) are widely recommended to preserve lean mass during GLP-1 therapy.
Deep dive
Body Composition: complete reference
Body composition refers to the proportion of fat, muscle, bone, and water in the body — a more meaningful health metric than weight alone. Standard measurements: lean body mass (everything not fat), fat mass, body fat percentage, visceral fat (around organs vs subcutaneous fat under skin), and muscle mass. Measurement methods range from simple (skinfold calipers, bioelectrical impedance scales) to sophisticated (DEXA scan, MRI, hydrostatic weighing). Body composition matters because two people с the same weight + BMI can have dramatically different metabolic risk based on fat distribution. GLP-1-induced weight loss historically caused concerns about disproportionate lean-mass loss — DEXA-based analyses of STEP and SURMOUNT trial subgroups suggest ~25-40% of total weight loss comes from lean tissue without intervention. Strategies для preserving lean mass during GLP-1 weight loss: adequate protein (0.7-1g per pound goal weight), resistance training 2-3×/week, and avoiding excessive caloric deficit beyond what GLP-1 naturally creates.
- In practice
- You lose 30 lbs on Wegovy. Without protein + resistance training, ~10 lbs may be lean mass (muscle/bone) — leaving you weaker. With protein + lifting, lean mass loss minimized.
- Clinical context
- Body composition tracking (DEXA, BIA) is more clinically meaningful than weight alone during pharmacological weight loss.
Medications
Body Composition is most directly relevant to the following GLP-1 medications:
Related terms
- Lean Mass — Body weight excluding fat — primarily skeletal muscle, organs, bone, and water. Preserving lean mass…
- BMI (Body Mass Index) — Body mass index is weight (kg) divided by height (m) squared. FDA labels for Wegovy and Zepbound req…
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GLP1Zoom glossary is educational reference. Definitions are summary interpretations of clinical sources and not a substitute for prescribing-information detail. Full disclaimer.
References
Glucagon-Like Peptide-1 Receptor Agonists: Mechanisms и Clinical Use (Drucker, Cell Metabolism)(2018)
Tirzepatide GIP/GLP-1 Dual Agonism: Mechanism Review (Lancet Diabetes & Endocrinology)(2021)
GLP-1 Effects on Gastric Emptying: Pharmacology Review (American J Physiology)(2020)
Endocrine Society Clinical Practice Guideline: Pharmacological Management of Obesity(2015)
STEP-1 trial: Once-Weekly Semaglutide in Adults with Overweight or Obesity (Wilding et al., NEJM)(2021)
SURMOUNT-1 trial: Tirzepatide Once Weekly для Treatment of Obesity (Jastreboff et al., NEJM)(2022)
SUSTAIN-6 trial: Semaglutide and Cardiovascular Outcomes (Marso et al., NEJM)(2016)
SURPASS-2 trial: Tirzepatide vs Semaglutide в Type 2 Diabetes (Frias et al., NEJM)(2021)
LEADER trial: Liraglutide and Cardiovascular Outcomes в T2D (Marso et al., NEJM)(2016)