Obesity Definitions in Sarcopenic Obesity: Differences in Prevalence, Agreement and Association with Muscle Function

Background Sarcopenic obesity (SO) is associated with poorer physical performance in the elderly and will increase in relevance with population ageing and the obesity epidemic. The lack of a consensus definition for SO has resulted in variability in its reported prevalence, poor inter-definitional agreement, and disagreement on its impact on physical performance, impeding further development in the field. While sarcopenia definitions have been compared, the impact of obesity definitions in SO has been less well-studied. Objectives To compare 3 widely-adopted definitions of obesity in terms of SO prevalence, inter-definitional agreement, and association with muscle function. Design Cross-sectional. Setting GERILABS study, Singapore Participants 200 community-dwelling, functionally-independent older adults. Measurements We utilized three commonly-used definitions of obesity: body mass index (BMI), waist circumference (WC) and DXA-derived fat mass percentage (FM%). Sarcopenia was defined using Asian Working Group for Sarcopenia criteria. For muscle function, we assessed handgrip strength, gait speed and Short Physical Performance Battery (SPPB). Subjects were classified into 4 body composition phenotypes (normal, obese, sarcopenic and SO), and outcomes were compared between groups. Results The prevalence rate for SO was lowest for BMI (0.5%) compared to FM% (10.0%) and WC (10.5%). Inter-definitional agreement was lowest between BMI and WC (kappa=0.364), and at best moderate between FM% and WC (kappa=0.583). SO performed the worst amongst body composition phenotypes in handgrip strength, gait speed and SPPB (all p<0.01) only when defined using WC. In regression analyses, SO was associated with decreased SPPB scores (beta=-0.261, p=0.001) only for the WC definition. Conclusion There is large variation in the prevalence of SO across different obesity definitions, with low-to-moderate agreement between them. Our results corroborate recent evidence that WC, and thus central obesity, is best associated with poorer muscle function in SO. Thus, WC should be further explored in defining obesity for accurate and early characterization of SO among older adults in Asian populations.