GLP-1 and Muscle Loss: What Research Shows and How to Track It
GLP-1 medications drive significant weight loss -- but research shows a meaningful portion can be muscle. Here is what the data shows and which blood markers track lean mass preservation.
Quick Summary Published analysis of GLP-1 clinical trials shows that approximately 25-40% of weight lost on semaglutide and tirzepatide is lean mass, not fat. Preserving muscle during GLP-1 therapy is one of the most important and under-discussed aspects of these protocols. This article is for educational purposes only and does not constitute medical advice.
The Muscle Loss Problem
The STEP trials for semaglutide and SURMOUNT trials for tirzepatide show dramatic weight loss -- 15-22% of body weight in many participants. Body composition analysis consistently shows a significant portion of weight lost is lean mass.
Research from SURMOUNT-1 showed participants on tirzepatide lost an average of 18.4% of total body weight, approximately 30-35% of which was lean mass by DEXA analysis.
Track your muscle preservation markers at [myprotocolstack.com/labs](https://myprotocolstack.com/labs).
Blood Markers That Track Lean Mass
Creatinine -- A metabolic byproduct of muscle. Declining creatinine during a GLP-1 protocol suggests lean mass loss. Research reference: 0.7-1.2 mg/dL for adult males.
BUN (Blood Urea Nitrogen) -- Low BUN alongside low albumin suggests inadequate protein intake.
Albumin -- Primary protein in blood plasma. Research reference: 3.5-5.0 g/dL. Values below 3.8 are worth addressing.
Prealbumin -- More sensitive than albumin for detecting acute nutritional changes.
IGF-1 -- Research shows caloric restriction often accompanying GLP-1 can reduce GH pulsatility and IGF-1 over time.
Research-Informed Strategies for Muscle Preservation
Published research identifies: higher protein intake (1.2-1.6g per kg body weight during active weight loss), resistance training (multiple RCTs show it preserves lean mass during caloric restriction), and in some emerging research, GH-releasing peptides alongside GLP-1. All clinical decisions require provider guidance.
Connecting Your Protocol to Your Blood Work
The [MyProtocolStack labs tracker](https://myprotocolstack.com/labs) lets you enter your full panel and track muscle markers across draws. [StackAI](https://myprotocolstack.com/stackai) analyzes the pattern flagging declining creatinine, albumin trends, and IGF-1 changes.
FAQ
How much muscle loss is normal on semaglutide?
Published data suggests 25-40% of total weight lost is lean mass in most participants not doing structured resistance training.
Can I prevent muscle loss completely on GLP-1?
Research suggests you can significantly reduce lean mass loss with resistance training and adequate protein -- but complete prevention during active weight loss is difficult.
Should I get blood work before starting a GLP-1?
Yes. At minimum: CBC, CMP, HbA1c, lipid panel, and thyroid function.
Do GH peptides prevent muscle loss on GLP-1?
There is emerging interest and some early clinical data but no large published RCTs. This is a conversation for your prescribing provider.
What is the best protein source for muscle preservation on GLP-1?
Research does not strongly differentiate between high-quality protein sources. Total protein intake appears more important than source.
*This article is for educational purposes only. It does not constitute medical advice.*
*Written by the MyProtocolStack team. Last updated: February 2026.*
Enter your blood work in MyProtocolStack, run StackAI analysis, and get personalized insights based on your actual numbers — not generic charts.
Start Free →