Body size phenotypes and low muscle mass: the Korean sarcopenic obesity study (KSOS).

CONTEXT: Unique subsets of body size phenotypes seem to be more prone or more resistant to the development of obesity-associated metabolic disorders, although the underlying mechanism is not yet clearly understood.

OBJECTIVES: We investigated the prevalence and risk of low muscle mass in subjects who are classified as either metabolically healthy normal weight (MHNW), metabolically abnormal but normal weight (MANW), metabolically healthy obese (MHO), or metabolically abnormal obese (MAO). Subjects were classified based on body mass index and presence of metabolic syndrome.

METHODS: Thigh muscle cross-sectional area was evaluated using computed tomography as an index of muscle mass in 492 apparently healthy adults enrolled in the Korean Sarcopenic Obesity Study (KSOS), an ongoing prospective observational cohort study. Low muscle mass was defined as thigh muscle cross-sectional area divided by weight (percent) of <1 SD below the mean values of young adults in both sexes.

RESULTS: The prevalence rates of low muscle mass in MHNW, MANW, MHO, and MAO subjects were 6.2%, 17.8%, 23.2%, and 33.7%, respectively. In a multiple logistic regression analysis, men with the MANW phenotype showed a remarkably increased risk of low muscle mass (odds ratio = 11.30, 95% confidence interval, 1.73-73.28) compared with those with MHNW. Furthermore, in both men and women, MHO or MAO subjects had higher odds ratios of low muscle mass compared with MHNW subjects.

CONCLUSIONS: The present study suggests that low muscle mass may be associated with different metabolic consequences according to body size phenotype.