Ability of fat and fat-free mass percentages to predict functional disability in older men and women

OBJECTIVES: Previous studies suggest an association between body composition and declining functional ability in older people. This study examined the relation between functional disability and percentage of fat mass (FM) and percentage of fat-free mass (FFM) in older men and women. DESIGN: Cross-sectional and prospective. SETTING: Rancho Bernardo, California. PARTICIPANTS: Subjects consisted of 1,051 ambulatory, community-dwelling Caucasian men and women, age 55 to 92, who attended a clinic visit between 1988 and 1992 and a subsequent clinic visit between 1992 and 1996. MEASUREMENTS: Measured at both visits, percentage of fat mass and percentage of lean body mass were estimated by bioelectric impedance analysis and functional disability was ascertained by self-administered questionnaire. Functional disability was dichotomized into those having any difficulty with a set of tasks versus those having no difficulty with the tasks. Two measures of functional disability were used: "lower body" disability, consisting of two lower motor tasks (walking 2-3 blocks and climbing up 10 stairs) and "overall" disability, consisting of nine tasks representing upper and lower body function and mobility. RESULTS: Compared with men, women were more likely to report both lower body and overall functional disability (P=.001). Cross-sectionally, a significant positive association was shown between fat mass and overall functional disability and a significant negative association was shown between FFM and overall functional disability in both men and women. Prospectively, increased percentage of body fat and decreased percentage of FFM were significantly associated with decreased functional ability in both women and men. All results were adjusted for age, smoking, alcohol use, physical activity, current estrogen use, depression, chronic disease, and education. CONCLUSION: Increased percentage of fat mass and decreased percentage of FFM are associated with greater functional disability in older men and women. Further research is needed to assess the relative importance of decreasing fat percentage or increasing fat-free percentage to preserve or improve functional ability in older people.