Meta-analysis puts a number on what resistance training changes about lean mass

A systematic review and meta-analysis published March 24, 2026 in Diabetes, Obesity and Metabolism pooled 20 randomized controlled trials covering 15,782 adults with overweight or obesity and tried to answer a question that has followed GLP-1 drugs since they became popular: how much of the weight people lose is lean mass, and how does that compare with losing weight through diet and exercise ^[1].

The answer, according to the authors, is that the proportions look broadly similar — except when resistance training is part of the plan ^[1].

What the analysis found

Across the incretin-based therapies, lean mass made up 25% to 39% of total weight lost ^[1]. Broken out by drug, the pooled estimates were 35.2% for semaglutide (95% confidence interval 31.5–38.9), 25.4% for tirzepatide (22.8–28.0) and 26.8% for liraglutide (23.1–30.5) ^[1].

Lifestyle interventions alone produced a comparable proportion: 26.2% (24.1–28.3). The comparison between drug therapy and lifestyle was not statistically significant (p = 0.42) ^[1].

The standout number was for lifestyle plus resistance training, where lean mass accounted for 17.5% of weight lost (14.2–20.8) — what the authors call the most favorable profile in the analysis ^[1].

The researchers searched PubMed, Embase, Cochrane CENTRAL and Web of Science from inception through January 20, 2026, and included only randomized trials of semaglutide, tirzepatide, liraglutide or lifestyle interventions that measured body composition with dual-energy X-ray absorptiometry (DXA) or MRI ^[1]. The co-primary outcomes were the absolute change in lean mass in kilograms and the share of total weight loss attributable to lean mass ^[1]. Data were pooled with random-effects models, risk of bias was assessed with Cochrane RoB 2, and the certainty of evidence was rated using GRADE ^[1]. Heterogeneity across studies was moderate (I² = 68%), and the authors reported no evidence of publication bias (Egger's test p = 0.23) ^[1].

The study was registered with PROSPERO (CRD420261277555), and the two authors — based at Community Health Partners in Fresno, California, and the Faculty of Medicine at Damascus University — declared no conflicts of interest ^[1].

Why it matters for patients

The worry many people have is that GLP-1 medications strip muscle in a way that dieting does not. This analysis does not support that framing: the proportion of weight lost as lean mass with semaglutide, tirzepatide or liraglutide was statistically indistinguishable from lifestyle intervention alone ^[1].

The more actionable finding is about resistance training. In the trials where it was added to lifestyle intervention, the lean-mass share of weight loss was roughly a third lower than in any other group analyzed ^[1]. The authors conclude that muscle mass "can be significantly preserved by integrating resistance training, adequate protein intake, and body composition monitoring into weight-loss treatment programs" ^[1].

There are real limits to what these numbers can tell an individual. This is a pooled comparison across separate trials, not a head-to-head randomized test of one drug against another or of a drug with versus without strength training. The reported resistance-training estimate came from lifestyle trials, so whether adding resistance training to semaglutide or tirzepatide produces the same 17.5% figure is not established by what the abstract reports ^[1]. Moderate heterogeneity (I² = 68%) also means the individual trials did not all point to identical results ^[1].

Several details are not available in the published abstract: the absolute lean mass changes in kilograms, the length of the included trials, the doses used, participants' ages, and the final GRADE certainty rating for each outcome ^[1]. The authors also note that lean mass loss during substantial weight reduction is "substantial" regardless of how the weight comes off ^[1].

What happens next

The paper appears in Volume 28, Issue 6 of Diabetes, Obesity and Metabolism, pages 4818–4827, with first publication online March 24, 2026 ^[1]. The full extracted dataset and study-level characteristics are published in the article's supporting information files, and the peer review history is publicly posted ^[1]. No new primary data were collected for this review — every figure comes from previously published randomized trials ^[1].

What this analysis does not settle is the clinical question underneath the percentages: whether the lean mass lost during GLP-1 treatment translates into measurable losses in strength, function or bone health over time. That would require trials designed to track those outcomes directly, and none are described in this report ^[1]. Anyone weighing how to approach body composition during treatment should discuss it with their own clinician.