Identification of Sarcopenic Obesity by Fat-to-Muscle Ratio in Older Adults: A Cohort Study

The diagnosis of sarcopenic obesity has been established in Europe and Japan, but screening tools remain inconsistent and lack standardization. The fat-to-muscle ratio (FMR) is a potential screening measure for sarcopenic obesity; however, its diagnostic accuracy compared with other tools has not been evaluated. This study compared the diagnostic performance of several screening tools for sarcopenic obesity.

This cross-sectional analysis used data from the National Center for Geriatrics and Gerontology Study of Geriatric Syndromes (NCGG-SGS), a national cohort study conducted in Japan. In total, 7916 community-dwelling older adults (mean ± standard deviation age 73.5 ± 6.2 years, 54.8% females) were included. Sarcopenic obesity was diagnosed by the Japanese Working Group on Sarcopenic Obesity (JWGSO) criteria. The FMR and phase angle (PhA) were measured using the bioelectrical impedance analysis (BIA).

Logistic regression analysis indicated that most screening tools, treated as continuous variables, were independently associated with sarcopenic obesity after adjustment for covariates; FMR (female: per 1-SD odds ratio [OR] = 3.06, 95% confidence interval [CI] = 2.53-3.71; male: OR = 3.09, 95% CI = 2.67-3.58), BMI (female: OR = 2.85, 95% CI = 2.35-3.58; male: OR = 1.43, 95% CI = 1.26-1.62), waist circumference (WC) (female: OR = 2.26, 95% CI = 1.86-2.74; male: OR = 1.24, 95% CI = 1.08-1.41) and PhA (female: OR = 1.12, 95% CI = 0.93-1.34; male: OR = 0.65, 95% CI = 0.56-0.76). Receiver operating characteristic (ROC) analysis showed moderate predictive ability for each screening tool: FMR (female: area under the curve [AUC] = 0.82, 95% CI = 0.79-0.85; male: AUC = 0.81, 95% CI = 0.79-0.84), BMI (female: AUC = 0.76, 95% CI = 0.72-0.79; male: AUC = 0.55, 95% CI = 0.51-0.59), WC (female: AUC = 0.70, 95% CI = 0.66-0.75; male: AUC = 0.53, 95% CI = 0.49-0.57) and PhA (female: AUC = 0.63, 95% CI = 0.58-0.69; male: AUC = 0.70, 95% CI = 0.67-0.74).

The findings suggest that the FMR is a more effective screening tool for identifying sarcopenic obesity than BMI, WC or PhA among community-dwelling older adults. Longitudinal studies are needed to confirm its predictive value across broader populations.