Energy balance
GLP-1 receptor agonist therapy induces predictable reductions in fat-free mass (approximately 30-40% of total weight loss) due to sustained negative energy balance, not direct catabolic effects.
Expect that about a third of your weight loss on GLP-1s will be muscle/fluid, not just fat. This is normal physiology, not a side effect. To mitigate this, prioritize protein intake and resistance training, especially if you have low testosterone.
GLP-1 receptor agonist therapy induces substantial total weight loss that includes predictable reductions in fat-free mass... lean mass reduction during GLP-1 RAs therapy appears to reflect the physiological consequences of sustained negative energy balance rather than a direct catabolic effect of GLP-1 receptor signaling.
Why this rating
Based on large randomized clinical trials (STEP 1, SURMOUNT-1) with DEXA sub-analyses.
Source
Testosterone Replacement Therapy as a Potential Strategy to Preserve Lean Mass in Men With Persistently Low Serum Testosterone Receiving GLP-1 Receptor Agonists: A Narrative Review
Luis M Canal de Velasco et al. · Cureus · 2026
DOI 10.7759/cureus.105734
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