Looking beyond fat in obesity: the frequently overlooked importance of muscle mass.

Obesity is traditionally defined as "abnormal or excessive fat accumulation that presents a health risk," yet this definition lacks precision and fails to account for individual variability in body composition. The continued reliance on body mass index (BMI) as a diagnostic tool further complicates accurate assessment, as BMI does not differentiate between fat mass and lean mass. Emerging evidence highlights that health risks associated with obesity are not solely determined by fat accumulation, but also by the relative deficiency in fat-free mass, particularly muscle. Despite this, the role of muscle health in obesity management remains underappreciated in clinical practice. With the advent of potent pharmacotherapies for obesity, such as a new class of GLP-1 receptor agonists, there is growing concern about their impact on muscle mass during weight loss. This underscores the need for a more holistic understanding of body composition changes and their implications for long-term health. This special issue of Reviews in Endocrine and Metabolic Disorders addresses these critical gaps, offering diverse perspectives on integrating muscle health into the continuum of obesity care.