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Muscle Loss From GLP-1 Drugs May Not Start in the Muscle

A lab study on human muscle cells questions whether GLP-1 weight-loss drugs directly cause the muscle loss seen in patients.

By Dr. Josh Axe · November 12, 2026 · 1 source · Watch

Photo: Pexels

A lab study published November 4, 2026 in GeroScience found that semaglutide and GIP did not directly trigger muscle-wasting programs in human muscle cells grown in a dish, despite the well-documented lean mass loss seen in patients on GLP-1 drugs.

Researchers isolated immature muscle cells from skeletal muscle biopsies of older adults with obesity undergoing orthopaedic surgery, then grew them into mature muscle fibers called myotubes. Genetic material for the GIP receptor appeared consistently across all donors, while genetic material for the GLP-1 receptor was undetectable by standard testing; a more sensitive imaging test in three donors found low-level GLP-1 receptor protein on the surface of 51% to 66% of the immature muscle cells. When mature fibers were treated with semaglutide or GIP, neither drug changed the activity of genes linked to muscle breakdown, and neither altered the mix of proteins released by the cells, with no protein changes reaching statistical significance.

Semaglutide did reduce the cells' glycolytic and total energy-production rates, with lower lactate release alongside it, pointing to a modest slowdown in one fuel pathway, while mitochondria, the cells' fuel-burning energy system, were unaffected. Neither semaglutide nor GIP damaged fiber thickness or the cells' ability to form new fibers; GIP increased fiber thickness after 8 days in culture.

The authors concluded that direct activation of these two receptors did not produce major muscle-wasting, inflammatory, structural, fiber-forming or energy-system effects in human muscle cells. They wrote that this fits an indirect explanation for the lean mass loss reported in patients on these drugs: the muscle loss more likely traces to eating less food and moving less during rapid weight loss, rather than the drug acting on muscle tissue directly.

GLP-1 Receptor Detection in Muscle Cells

GeroScience, 2026, Ditchfield et al.

This is a lab-dish experiment on isolated human muscle cells, not a study of people taking the drugs, so it cannot show what happens to muscle over months of real use, including whether lower food intake and reduced mechanical loading fully explain the lean mass loss seen in trials. Larger studies following actual patients are the next step to confirm this indirect-cause explanation.

Dr. Axe’s Take

This lab study suggests muscle loss on these drugs likely comes from eating less and moving less during rapid weight loss, not the drug attacking muscle directly. I pair GLP-1-class medicines with a whole-food diet, high protein, fiber-rich vegetables and legumes, plus regular resistance training to protect muscle during fast weight loss. Many people do well on a much lower dose, often 10 to 20% of the labeled dose, worked out with the prescribing doctor rather than adjusted on their own. Watch for nausea, reduced protein intake, and strength loss if resistance training isn't included.

— Dr. Axe

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Study summary

Who: Muscle cells grown from skeletal muscle biopsies of older adults with obesity undergoing orthopaedic surgery.
Design: Lab-dish study: primary human myotubes treated with semaglutide or GIP peptide, assessed by gene expression, secretome, bioenergetics and imaging tests.
Dose: Not reported (cell-culture treatment concentrations, not a patient dose)
Primary result: Neither semaglutide nor GIP altered atrophy-related gene expression or the secretome; no proteins reached statistical significance.
Secondary: Semaglutide lowered glycolytic and total ATP production with reduced lactate secretion; mitochondria unaffected. GIP increased myotube thickness after 8 days; GLP-1 receptor protein detected on 51-66% of cells in 3 donors.
Funding / conflicts: Funder listed in the journal record: Birmingham Biomedical Research Centre. Competing interests: The authors declare no competing interests.
Date: Nov 4, 2026