Changes in body composition, muscle function, and muscle insulin sensitivity induced by obesity and bariatric...

Sarcopenic obesity, defined by the coexistence of excess adiposity and sarcopenia, represents an emerging clinical concern. Bariatric surgery, an effective treatment option for obesity, induces muscle mass loss, raising concerns about the potential development or worsening of sarcopenia. However, bariatric surgery improves body composition, notably the muscle-to-fat ratio, and muscle function, suggesting that the overall risk of sarcopenic obesity may actually decrease after bariatric surgery. The mechanisms underlying this paradox are not well characterized. Obesity profoundly alters skeletal muscle homeostasis, leading to insulin and anabolic resistance that contribute to type 2 diabetes and sarcopenia well before old age. In contrast, bariatric surgery, despite inducing muscle mass loss, improves or even reverses obesity-related alterations in muscle phenotype and oxidative metabolism, while reducing myosteatosis, inflammation and insulin resistance, thereby promoting overall improved muscle metabolic and functional health. This review examines how obesity and bariatric surgery affect skeletal muscle mass, function and insulin sensitivity, and discusses the implications of these alterations for the development, worsening, or remission of sarcopenic obesity after bariatric surgery.