Recently, the glucagonlike peptide 1 (GLP-1) receptor agonist semaglutide has changed the obesity treatment landscape. This and other similar medications approaching the market are in high demand because of their ease of use, effectiveness, and lack of interactions with other medications.
Semaglutide is a weekly subcutaneous injection approved by the U.S. Food and Drug Administration for weight loss in conjunction with lifestyle change. It elicits an average weight loss of 15%-18% from baseline in adults with overweight or obesity (body mass index ≥ 27 with at least one obesity-related comorbidity or BMI ≥ 30) in a period of 52-68 weeks (Wilding et al; Rubino et al). Liraglutide is a daily GLP-1 agonist, which is FDA approved for treatment of overweight, with an average weight loss of 8% from treatment start.
Though GLP-1 agonists are very effective for weight loss, questions about side effects have arisen.
Current modalities of weight loss don’t specifically target fat mass (FM), so it is expected that, to a degree, fat-free mass (FFM), including muscle mass, will also be lost along with fat mass.
Loss of muscle mass is associated with an increased risk for lower bone density, fatigue, injuries, and decreased strength. In addition, sarcopenic obesity, a combination of high body fat percentage and low skeletal muscle mass, is concerning in patients older than 65 years and/or postmenopausal patients. Because GLP-1 agonists cause more rapid and sustainable weight loss, compared with intensive behavioral lifestyle therapy, there has been more media attention recently about possible muscle mass loss with GLP-1–agonist use.
However, proper well-rounded approaches to obesity treatment can mitigate the issue of muscle mass loss even when rapid weight loss occurs. When weight loss is achieved with very-low-calorie dietary changes alone (without exercise), it is also associated with significant reductions in lean muscle mass; however, incorporating exercise, preferably resistance training, can mitigate the muscle mass loss. The muscle-preserving effect of exercise is especially prominent in older populations where it is needed most and should be incorporated (Armanento-Villareal et al.; Winter et al.; Batsis and Zagaria; Mason et al.).
Furthermore, studies in rat models demonstrate liraglutide induces myogenesis in myoblasts and protects against muscular atrophy. In human studies, GLP-1 infusion was associated with an improved skeletal and cardiac muscle microvasculature, suggesting that GLP-1 agonists may have some positive effects on the muscle. A 2020 systematic review examined the effect of gradual vs. rapid weight loss and demonstrated no significant difference in muscle loss between the rapid weight-loss group and gradual weight-loss group. Even after gastric bypass surgery, most of the muscle mass loss occurred during the first year, when weight loss is happening. However, after the first year, skeletal muscle was maintained even without introducing additional dietary or exercise interventions.
Age, although a consideration, should not be a discriminating factor against treating obesity. Sarcopenic obesity is a serious risk especially in patients aged 65 years or older, but GLP-1–agonist therapy can be beneficial to prevent muscle atrophy and increase blood flow to skeletal and cardiac muscle. In addition, patients must be encouraged to maintain an appropriate dietary and exercise regimen to treat their obesity. Management of obesity is complex and multifaceted, and patients should understand their responsibility to follow clinician recommendations during this journey to decrease the associated side effects.
Overall, with any level of weight loss achieved with current strategies, a certain amount of muscle mass loss is expected. All efforts to actively preserve muscle mass can prevent too much muscle loss.
Therefore, providers prescribing medications like GLP-1 agonists to treat obesity must also counsel patients about incorporating aerobic exercise and resistance training as part of the treatment plan as well as ensuring they eat a high-protein diet. Generally, resistance training is preferred over aerobic exercise for muscle mass preservation and increased strength, but studies also demonstrate benefit with aerobic exercise.
In the first few visits of initiating obesity treatment, patients should be encouraged to start to incorporate light physical activity as tolerable while starting to make dietary changes to include at least 0.8g/kg/day of protein (Fappi et al.). These initial visits are also an important opportunity for clinicians to ingrain the importance of exercise as part of healthy weight loss. At every visit, physical activity level should be assessed.
Dr. Ahn is a clinical fellow in obesity medicine, Weight Management Center, at Massachusetts General Hospital, Boston. Dr. Singhal is an assistant professor of pediatrics, Harvard Medical School, Boston, and director, Pediatric Program, MGH Weight Center, Massachusetts General Hospital. Dr. Singhal reported that his spouse consults with AstraZeneca, Dilachi Pharma, Eli Lilly, Genetech, Immunomedics, Pfizer, Sanofi, and Novartis.
A version of this article first appeared on Medscape.com.