What the Research Shows Recent research on semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) has revealed concerning trends about body composition changes: A 2023 analysis of STEP trial data found that approximately 39% of weight lost on semaglutide was lean body mass 1 Research on tirzepatide showed similar patterns, with 30-40% of total weight loss coming from lean tissue 2 Comparative studies indicate GLP-1 users may lose more muscle than people losing weight through diet and exercise alone 3 For context: if you lose 50 pounds on a GLP-1 medication, 15-20 pounds might be muscle mass
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In a typical healthy weight loss scenario, about 75 percent of weight loss comes from fat, while roughly 25 percent comes from fat-free mass, including muscle, says Sriram Machineni, MD, an endocrinology, diabetes, and metabolism expert at Montefiore Health Systems in New York City
