Body Composition
The proportions of fat, muscle, bone, and water in the body. Weight management trials increasingly assess body composition changes (using DEXA scans) to distinguish fat loss from lean mass loss. Preserving lean mass during weight loss is an important clinical consideration.
Technical Context
Assessment methods: DEXA (dual-energy X-ray absorptiometry — gold standard for clinical trials, measures total and regional fat mass, lean mass, and bone mineral content), BIA (bioelectrical impedance analysis — less accurate but portable and inexpensive), air displacement plethysmography (Bod Pod), CT/MRI (most accurate for regional fat distribution including visceral fat quantification, but costly and involves radiation for CT), and D2O dilution (total body water, research use). Body composition during pharmacological weight loss is a critical concern: ideally, weight loss should be predominantly fat with minimal lean mass loss. GLP-1 RA-induced weight loss typically comprises 60-70% fat mass and 30-40% lean mass — the lean mass component is a concern because lean mass loss can reduce basal metabolic rate and functional capacity. Strategies to preserve lean mass during pharmacotherapy: resistance exercise and adequate protein intake (1.2-1.6 g/kg/day).