GLP-1 drugs shed mostly fat while largely sparing lean mass, meta-analysis finds

Obesity-treating GLP-1 receptor agonists (GLP-1 RAs) are now among the most widely used drugs in medicine. A major concern is that weight loss from these drugs might also erode skeletal muscle, which could raise the risk of sarcopenia, especially in older or frail adults. Because muscle mass underpins metabolic health, mobility, and healthspan, the composition of lost weight matters as much as the number on the scale. This review tried to quantify that trade-off across individual agents.

The team from Poznan University of Medical Sciences registered the protocol in PROSPERO (CRD420251002447) and searched PubMed, Scopus, and Web of Science through December 2024 following PRISMA guidelines. They included adults with overweight or obesity, with or without type 2 diabetes, treated with GLP-1 RAs or dual GIP/GLP-1 agonists. Eligible studies reported body composition by BIA, DXA, MRI, or CT at 3, 6, or 12 months. Thirty-six studies were included qualitatively. Twenty-four, covering 1,032 patients, were pooled using random-effects models with subgroup analyses by drug and duration.

The studies came mainly from Europe and Asia. Most reported 6-month outcomes, and liraglutide and semaglutide were the most frequently studied agents, usually given subcutaneously. Body composition was measured most often by bioelectrical impedance (BIA), then DXA. At 3 months, mean body weight fell by roughly 9%, with marked reductions in fat mass and visceral adipose tissue. GLP-1 RA treatment consistently lowered body weight, BMI, and waist circumference at every time point.

At 6 months, average weight reduction was about 5%, with semaglutide, liraglutide, and exenatide showing comparable effects. Lean mass remained largely preserved. At 12 months, weight loss persisted at around 4%, but results varied between agents, most notably for liraglutide. Across the pooled studies, fat mass loss predominated and reductions in lean body mass were modest. The smaller percentages at later time points should be read cautiously, because each time point drew on a different set of studies and populations rather than following the same patients.

The authors frame these findings as 'quality' weight loss. They point to mechanisms that may protect muscle, including improved insulin sensitivity, less ectopic fat, and preclinical evidence of effects on muscle glucose uptake and atrophy pathways. They still stress that modest lean mass losses can occur during large weight reductions. In patients at high risk of sarcopenia, they recommend nutritional optimization and resistance training alongside therapy, with agent selection individualized.

Several caveats apply. Included studies were heterogeneous in design, drug, dose, and population, and many were small, retrospective, or single-arm. Body composition methods varied, and BIA is less accurate than DXA for lean mass. Only 3-, 6-, and 12-month follow-ups qualified, and only English-language reports. The pooled figures are therefore best viewed as estimates of direction and magnitude rather than precise head-to-head comparisons. The excerpt provided did not include p-values, confidence intervals, heterogeneity statistics, or the risk-of-bias results.