The fat mass index, not the fat-free mass index, is associated with impaired physical performance in older adult subjects: Evidence from a cross-sectional study.

BACKGROUND: Impaired physical performance (IPP) and physical disability (PD) are two serious public health problems in older adult populations worldwide. While studies show that changes in body composition are important risk factors for developing these conditions, there is little evidence that the fat-free mass (FFM) and fat mass (FM) indices (FFMI and FMI, respectively) are associated with IPP in older men and women. This study assessed the association among FFMI, FMI, and IPP using Short Physical Performance Battery (SPPB) in Mexican men and women aged over 60 years.

METHODS: This cross-sectional study included 217 older people (men 34.6%, women 65.4%; 60-92 years). FFM and FM were assessed by dual X-ray absorptiometry, assuming a two-compartment model. FFM and FM were adjusted by height squared and the indices were obtained. After assessment of physical performance by SPPB, subjects with scores ≤6 were classified as having IPP. Associations were tested by multiple logistic regression analysis in separated models.

RESULTS: IPP prevalence was 14.3%. Women were affected more than men. Regression analysis showed no significant association between FFMI and IPP, but FMI was strongly-associated, as for each unit increase in FMI, the risk of IPP rose significantly (OR: 1.14), and this result remained significant after adjusting for age, comorbidity, polypharmacy, and the appendicular skeletal muscle mass index (OR: 1.23; p ≤ 0.001). These results emphasize the importance of preventing increases in FM and avoiding overweight and obesity in older men and women.