Time-dependent variation in weight and body composition in healthy adults

Objectives: To define the limits of change in body weight and body composit ion after different time intervals in healthy, normal adults. Methods: Pros pective and retrospective analyses of paired body composition studies in a total of 326 healthy adults, ages 18 to 97. Measurements included body weig ht, fat and fat-free mass (FFM) by dual x-ray absorptiometry (DXA) and bioi mpedance analysis (BLA), plus body cell mass (BCM) by whole-body counting o f K-40 and BIA. Results: Time interval between studies was a significant pr edictor of the differences in paired studies. The 95% confidence intervals for percent difference were lowest for body weight, intermediate for BCM an d FFM, and highest for fat, in part because of the differences in sizes of these body compartments. There were significant associations among the chan ges in body composition by BIA and by criterion methods, suggesting that th e observed changes are real. Conclusions: The normal variation in body weig ht and body composition increases over time. Time-dependent criteria may in crease the sensitivity in diagnosing malnutrition. Interpreting changes in body compartments requires consideration of the size of each compartment.