Changes in Fat Mass have a Greater Impact on Physical Function in Elderly Women than Changes in Lean Mass

Abstract

Although lean mass is associated with physical function in older adults, the impact of changes in fat mass (FM) and lean soft tissue (LST) is not well characterized. PURPOSE: To determine the impact of changes in FM and LST on lower extremity physical function (LEPF) in community-dwelling elderly women over two years. METHODS: Elderly women (67.6±6.0 yrs, N = 197) were assessed for body composition via dual-energy X-ray absorptiometry and their LEPF was evaluated with a) stair ascend (ST-UP) and b) descend (ST-DN), c) 7 m walk (7M-W), d) 7 m obstacle walk (7M-OBW), and e) chair rise, walk and return (UP&GO). Average Z-score from all tests was used to estimate overall LEPF. RESULTS: Losers (n=60, lost >3% FM), Maintainers (n=62, ±3% FM), and Gainers (n=75, gained >3% FM) did not differ at baseline in LEPF or in body composition except in LST (42.5±6.2, 45.4±6.2, 43.7±5.6 kg, respectively, p=0.03). Over the 2 years, as expected, the Losers reduced and the Gainers increased in weight (-4.6±3.4, 2.6±2.4 kg, respectively), FM (-3.2±2.3, 2.5±1.4 kg, respectively), and body fat percentage (-2.3±2.2, 1.9±1.2 %, respectively, all p<0.01) and the Losers decreased in LST (-1.2±1.7 kg, p<0.01); however, the Maintainers had very small but significant losses of weight (-0.6±1.6 kg) and LST (-0.4±1.3 kg, both p=0.01) and gain in body fat percentage (0.2±0.7 %, p=0.01) with no change in fat mass (0.0±0.5 kg, p=0.97). Losers improved 5.2% in 7M-W (p<0.01), 4.0% in 7M-OBW (p=0.02), and 5.5% in UP&GO (p<0.01), and Maintainers improved 3.4% in ST-UP (p=0.03) and 5.9% in ST-DN (p<0.01), whereas Gainers decreased in overall LEPF (0.11±0.82 to -0.06±0.87 Z, p=0.01). Controlling for LST at baseline, 7M-W (p=0.01), UP&GO (p<0.01) and LEPF (p=0.04) interacted with participant grouping; Losers improved in performance but Maintainers or Gainers did not change or decreased slightly. No time by group interactions (all p>0.05) were found when the sample was split on two-year loss (>3%), maintenance (±3%), or gain (>3%) in LST. CONCLUSION: Changes in FM have more impact on LEPF than changes in LST among relatively healthy community dwelling older women. Lifestyle interventions to reduce FM may improve physical performance and reduce risk for disability in older women. Support: NIH RO1-AG020118, UIUC Research Board