Evidence review: Open Peptide Project (verified against primary PubMed, ClinicalTrials.gov & FDA records) · Last checked 2026-10-27. ← Back to Evidence Library

GLP-1 lean mass loss and muscle preservation

Name: GLP-1 lean mass loss and muscle preservation
Published: 2026-10-27

How much of incretin weight loss is muscle, and what is being studied to protect it

Evidence verdict: Moderate: a 2026 systematic review of 35 RCTs quantifies lean-mass loss; muscle-sparing add-on drugs remain investigational.

Last reviewed: Oct 27, 2026

In 30 seconds

In a 2026 systematic review, a median of about 28% of weight lost on incretin drugs came from muscle-based measures, wide range. [Controlled study, review]
No trial in that review measured objective physical function. Whether lean-mass loss causes harm is not established. [Controlled study, review]
A 12-month cohort of semaglutide users found lean mass fell early then stabilized, while grip strength improved. [Observational]
Muscle-preserving drugs such as bimagrumab are investigational; in a phase 2 trial, adding it to semaglutide increased weight loss. Not FDA-approved for this use. [Controlled study]

The size of the effect

Batsis et al. (Ann Intern Med 2026) included 35 RCTs of liraglutide, semaglutide, tirzepatide or dulaglutide. Median share of weight loss from muscle-based indices was 28.3% (IQR 15.9% to 39.9%); about 29% with BIA or DXA and about 25% with CT or MRI, with most studies above prespecified benchmarks. Only 28.6% made body composition a primary outcome, and none reported objective physical function (PMID 41996180). [Controlled study, systematic review] STEP 1 established semaglutide's weight effect in 1961 adults (PMID 33567185). [Controlled study]

Real-world data

SEMALEAN followed 106 completers with DXA for 12 months: mean weight loss 13%, fat mass down 18%, lean mass down about 3 kg by month 7 then stable, handgrip strength up, and sarcopenic obesity prevalence down from 49% to 33% (PMID 41068996). [Observational; no control group]

Investigational muscle-sparing drugs

Bimagrumab, an investigational antibody against type II activin receptors (sponsor not stated in the abstract; UNVERIFIED), was tested with semaglutide in 507 adults (NCT05616013). At week 48, the high-dose combination gave the largest mean weight change versus placebo; common side effects of bimagrumab were muscle spasms, diarrhea and acne (PMID 41772149). [Controlled study] Lean-mass results are not in the abstract (UNVERIFIED). Related compounds covered in this library include enobosarm, apitegromab and trevogrumab (see Batch P pages). WADA prohibits myostatin inhibitors and related agents under S4.3.

What is evidence-based now

A 2026 narrative review notes that DXA lean mass and BIA fat-free mass are not the same as skeletal muscle, that lean-tissue loss does not necessarily mean lost strength, and favors food-first nutrition counseling, adequate protein, structured resistance exercise and risk-based monitoring (PMID 42346344). [Review] The optimal protocol has not been tested head-to-head (UNVERIFIED). This page gives no supplement or dose advice.

Evidence levels used on this page

[Regulatory] FDA, USP or WADA primary document. [Controlled study] randomized trial or systematic review of trials. [Observational] market surveillance, pharmacovigilance or cohort data. [Lab] cell, analytical or animal work. [Case] single case report.

Enobosarm, Apitegromab, Trevogrumab

References

Batsis et al. Effect of incretin-based and nonpharmacologic weight loss on body composition: a systematic review. Ann Intern Med. 2026. PMID 41996180.
Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021. PMID 33567185.
Alissou et al. Impact of semaglutide on fat mass, lean mass and muscle function in patients with obesity: the SEMALEAN study. Diabetes Obes Metab. 2026. PMID 41068996.
Heymsfield SB, et al. Bimagrumab plus semaglutide alone or in combination for the treatment of obesity: a randomized phase 2 trial. Nat Med. 2026. PMID 41772149. NCT05616013.
Šantić et al. Lean mass and musculoskeletal preservation in GLP-1-based obesity treatment: nutrition, exercise, supplementation, and monitoring strategies. Metabolites. 2026. PMID 42346344.
World Anti-Doping Agency. 2026 Prohibited List (in force 1 January 2026), sections S0, S2.2 and S2.3. https://www.wada-ama.org/en/prohibited-list

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