Muscle is increasingly recognized as far more than the tissue that powers movement. It is a dynamic organ that influences metabolism, healthy aging, and lifespan. For more than two decades, Dr. Keith Baar has helped advance our understanding of muscle biology, revealing how nutrition and physical activity work together to build and maintain a healthy musculoskeletal system. Today, that expertise is informing an important conversation in weight management: how GLP-1 therapies affect muscle health during weight loss?
As these therapies become widely adopted, popular media have spread concerns that rapid weight loss may come at the expense of muscle. Much of that concern stems from clinical trials reporting that a substantial portion of weight loss came from lean body mass, a measurement that is often taken as a proxy for skeletal muscle.
For Dr. Baar; however, the question is more nuanced than it first appears. Lean body mass encompasses much more than skeletal muscle, it also includes connective tissue and other internal organs such as the heart, liver, and kidneys.
To move beyond indirect measures of lean body mass, Dr. Baar and collaborators conducted four preclinical studies in mice alongside a proof-of-concept clinical trial in patients with obesity, directly measuring muscle mass, muscle function, and body composition. Their findings, published in Cell Reports Medicine, showed that GLP-1 therapies predominantly reduced body fat while preserving muscle function in both mice and people. Although absolute muscle mass declined, body composition improved, strength was maintained in patients, and running performance improved in mice. Baar’s team also found that liver mass decreased more than skeletal muscle during weight loss, consistent with the well-established reductions in liver fat observed with GLP-1 therapies. These findings suggest that relying on lean body mass alone may overestimate muscle loss, as commonly used body composition scans do not distinguish changes in skeletal muscle from other lean tissues.
What really matters isn’t simply muscle mass, it’s whether people maintain the strength and function they need to live healthy, active lives. This also suggests that it is really important to be exercising while using the drugs.
Importantly, his team also found that skeletal muscle responded differently to GLP-1 therapy than it did to calorie restriction alone, revealing distinct changes in proteins associated with mitochondrial function and muscle remodeling. While the functional significance of these molecular changes remains to be determined, they open new avenues for understanding how GLP-1 therapies influence muscle metabolism, basal metabolic rate, and adaptation.
Together, these findings reinforce a broader message: muscle health is best understood through function, resilience, and metabolic performance – not simply muscle mass.
Beyond its implications for GLP-1 therapies, Dr. Baar’s research is guided by a broader question: how can nutrition and physical activity work together to build and maintain healthy musculoskeletal tissue?
His laboratory has helped define how dietary protein, specific amino acids, and mechanical loading work together to build stronger muscles and connective tissues, advancing our understanding of how nutrition and exercise support mobility, recovery, and healthy aging.
As consumer interest in protein continues to grow, Dr. Baar’s research is helping shift the conversation from how much protein we eat to how protein quality, amino acid composition, and bioavailability influence muscle adaptation, recovery, and metabolic health. These insights are driving innovation in next-generation proteins and functional ingredients designed to improve protein utilization and support musculoskeletal health throughout life.
More recently, Dr. Baar and collaborators challenged another common assumption – that simply consuming more protein is sufficient to maintain musculoskeletal health. In a study published in the American Journal of Clinical Nutrition, they found that providing older adults with an additional 40 grams of whey protein each day did not increase protein turnover in muscle, tendon, cartilage, bone, or other musculoskeletal tissues. Instead, the findings suggest that protein alone is not enough – physical activity is a critical signal that enables the body to effectively use dietary protein to maintain healthy tissues.
Food provides the building blocks, while exercise provides the stimulus to build bigger stronger structures
Together, this body of work exemplifies how advances in muscle biology can guide the development of evidence-based nutrition strategies that promote healthy aging, mobility, and metabolic resilience. IIFH’s collaboration with Dr. Keith Baar reflects a shared commitment to translating these discoveries into science-driven innovations that shape the future of food and human health.
