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

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