Age-related decrease in resting energy expenditure in sedentary white women: effects of regional differences in lean and fat mass

Background: Lean mass and rearing energy expenditure (REE) decrease with ag e. However, it is unknown whether age-related changes in regional lean and fat mass are responsible for the age-related decrease in REE. Objective: Our objective was to determine how regional lean and fat mass va ry with age and whether age is independently related to REE after adjustmen t for regional fat and lean mass. Design: The study was a cross-sectional evaluation of 58 white women aged 2 3-77 y. Regional and whole-body lean and fat mass were measured by dual-ene rgy X-ray absorptiometry, subcutaneous abdominal tissue (SAT) and intraabdo minal adipose tissue (IAF) by computed tomography, and REE by ventilated-ca nopy indirect calorimetry. Results: Independent of other significant correlates, age was significantly and independently associated with greater IAF (beta = 0.49) and less leg l ean mass (beta = -0.35). IAF (r = -0.28) and IAF:SAT (r = -0.31) correlated negatively with REE. REE was negatively associated with greater age (beta = -0.42), independent of changes in lean and fat mass in different parts of the body. By contrast, trunk lean (beta = 0.27) and leg fat (beta = 0.27) mass were associated with greater REE independent of age and other body-com position variables. Conclusions: These results suggest that trunk lean mass (presumably primari ly organ tissue) is relatively resistant to age-related changes in body com position, whereas muscle mass, especially leg muscle, tends to be lost. The se data also suggest that the age-related decreases in REE are not fully ex plained by changes in body composition.