A new study to be presented at this year’s European Congress on Obesity (ECO 2025, Malaga, Spain, May 11-14) showed that patients who used GLP-1 or GLP-1/GIP receptor agonist combination therapy for weight loss had minimal loss of lean muscle mass as they lost weight over a six-month treatment period. The study was conducted by Dr. Dinabel Peralta Reich of the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell. Dr. Alexandra Filingheri and colleagues at Lenox Hill Hospital, Northwell Health, New York City, New York, USA, and New York Weight Wellness Medicine, New York City, USA.
GLP-1 (glucagon-like peptide-1) receptor agonists, such as semaglutide and liraglutide, were originally used for type 2 diabetes, but have also proven effective in managing obesity and promoting weight loss. Recently, tirzepatide, a combination of GLP-1 and GIP (glucose-dependent insulinotropic polypeptide), was also approved for the treatment of type 2 diabetes and/or obesity. As research continues to support the use of these agents, monitoring body composition, particularly muscle mass and atrophy, remains clinically important. Obesity medicine experts play a critical role in designing interventions that promote weight loss while preserving lean body mass.
This 6-month prospective cohort study enrolled 200 adults (18-65 years, BMI ≥25 kg/m2, overweight or obese) prescribed either the GLP-1 receptor semaglutide or the GLP-1/GIP dual agonist tirzepatide, with 60% (n = 120) of participants receiving tirzepatide and 40% (n = 80) received tirzepatide. Semaglutide. Participants received education from a board-certified bariatric physician about medication use, strength training, and protein intake.
A system called InBody 570 was used to assess body composition at baseline, 3 months, and 6 months using bioelectrical impedance. InBody 570 is a professional body composition analyzer that uses multifrequency bioelectrical impedance analysis (BIA) to provide a detailed breakdown of muscle, fat, and water distribution. Measures total body water (intracellular/extracellular), skeletal muscle mass, body fat percentage, visceral fat, and regional muscle distribution.
Primary outcomes included changes in body fat and muscle mass, and data were analyzed using statistical modeling. Qualitative data regarding medication adherence, physical activity, and nutrition were also collected. Participants served as their own controls for pre- and post-intervention comparisons.
All 200 participants (99 men and 101 women) completed the study. The mean age was 47 years, and the mean baseline BMI was 31.4 kg/m² (although all were over 25 years old and living with either overweight or obesity). At 6 months of age, the average female weight decreased from 156 pounds (71 kg) to 137 pounds (62 kg), a 12% decrease. Meanwhile, the average weight of men decreased from 223 pounds (101 kg) to 193 pounds (88 kg), a decrease of 13%.
At six months, women lost an average of 10.8 kg (10.8 kg) of fat mass but only 1.4 lb (0.63 kg) of muscle mass, while men lost 25 lb (12 kg) of fat mass and only 2.4 lb (1 kg) of muscle mass.
Self-reported medication adherence was 95% at 3 months and 89% at 6 months. Qualitative data showed that regular resistance training and consistent protein intake were associated with improved muscle retention and strength. The study is ongoing and more data continues to be collected. The differences in body weight/lean mass/fat mass lost between tirzepatide and semaglutide are still being analyzed.
The authors say: ”This 6-month study demonstrates that GLP-1 and dual GLP-1/GIP receptor agonists effectively reduce body weight and fat mass in obese patients. Although some muscle loss is to be expected, research suggests that with close supervision from a specialist bariatric doctor, muscle loss can be minimized. Factors such as self-reported protein intake, medication compliance, and regular follow-up contributed to success. Data shows that these drugs help reduce body fat while preserving lean body mass. Further research is needed to better understand the role of diet and exercise in maintaining muscle mass.”
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European Obesity Research Association
