BMI, body composition, and physical functioning in older adults

Objective: Recent studies have emphasized the importance of muscle and fat mass in relation to age-related decline in physical function. Our objective was to determine whether BMI, as a surrogate measurement of fat mass, may be used as a measure of risk factor for physical functioning in older adults and whether body composition measurements confer any advantage over BMI. Research Methods and Procedures: Four thousand men and women >= 65 years of age living in the community, stratified by age and sex, underwent the following, measurements: body composition by DXA; grip strength; and timed 6-m walk. Subjects were grouped into five categories of BMI using Asian criteria for health-related risks, and between-group differences in physical performance measures and body composition were analyzed using analysis of covariance adjusting for age, physical activity level, and presence of chronic disease. Results: Subjects in the two obese categories had a significantly greater number of instrumental activities of daily living (IADL) impairments compared with the underweight and normal-weight groups. Those with BMI >= 30 kg/M-2 had the worst walking performance, and the groups with BMI in the normal and overweight range had optimal performance. Fat mass, but not appendicular muscle mass, was associated with walking speed after adjusting for BMI. Discussion: Fat mass seems to be a more important factor than appendicular muscle mass in determining walking speed in community-living older adults, even after adjusting for BMI.