GLP-1 Agonists May Preserve Muscle Mass During Weight Loss: Daily Dose

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Patient Care brings primary care clinicians a lot of medical news every day—it’s easy to miss an important study. The Daily Dose provides a concise summary of one of the website's leading stories you may not have seen.

On April 10, 2025, we reported on a new study that will be presented at the upcoming European Congress on Obesity (ECO 2025) in Malaga, Spain, that examined the changes in body fat and muscle mass among people with obesity using either the GLP-1 receptor semaglutide or the GLP-1 / GIP dual agonist tirzepatide.

The study

The prospective cohort study included 200 adults (99 men, 101 women, mean age 47 years) with overweight or obesity (BMI ≥25 kg/m²) and mean baseline weight of 31.4 kg/m². Participants received either the GLP-1 receptor agonist semaglutide (40%) or the GLP-1/GIP combination mimetic tirzepatide (60%). All participants were under the supervision of a board-certified obesity physician who provided education on medication use, resistance training, and protein intake. Researchers assessed body composition a baseline, 3 months, and at 6 months using bioelectrical impedance analysis with the InBody 570 system, which provides detailed measurements of muscle, fat, and water distribution. The researchers collected both quantitative data on body composition changes and qualitative information regarding medication adherence, physical activity, and nutrition.

The findings

After 6 months of treatment, the average weight of women decreased from 156 lbs (71 kg) to 137 lbs (62 kg), a reduction of 12%. The weight loss among men was similar, with an average decrease from 223 lbs ( 101 kg) to 193 lbs (to 88 kg), a 13% reduction. Reporting on the primary outcome, change in muscle and body fat mass, the investigators found that the composition of the weight loss was predominantly fat mass: women lost an average of 10.8 kg of fat mass and only 0.63 kg of muscle mass, while men lost 12 kg of fat mass and just 1 kg of muscle mass.

Authors' comments

“While some muscle loss is expected, the study suggests that, with close supervision by an expert obesity doctor, muscle loss can be minimized."

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