Association between lean mass and the risk of metabolic syndrome in Korean children and adolescents: data from the Korea National Health and Nutrition Examination survey.

Skeletal muscle is considered an endocrine and paracrine organ that has metabolic effects, and several studies have shown a positive association between muscle mass and insulin sensitivity. However, results on the relationship between muscle mass and metabolic syndrome in children and adolescents remain inconsistent. Body composition consists primarily of lean and fat mass, with lean mass being closely associated with body size. Since muscle constitutes a part of lean mass, the contribution of muscularity can be evaluated more accurately by assessing lean mass relative to fat mass, which is inversely associated with body size. This study utilized nationally representative data to assess the association between lean mass (measured via dual-energy X-ray absorptiometry) and the risk of metabolic syndrome. Model 1 was adjusted for age, sex, physical activity, alcohol consumption, smoking status, household income, and rural residence. Model 2 was based on Model 1 and the fat mass index. The odds ratio of lean mass was 1.6 (95% CI 1.4-1.8) and 2.0 (95% CI 1.8-2.3) in Model 2 and Model 1, respectively. However, the lean-to-fat mass ratio showed a strong inverse association with metabolic syndrome (adjusted odds ratio 0.2 [95% CI 0.1-0.3]), suggesting a protective effect of a greater proportion of lean mass relative to fat mass. These findings suggest that the balance of body composition plays an important role in metabolic risk. Both lean mass and fat mass need to be considered when evaluating metabolic risk in children and adolescents.