Submitted to: Advances in Food and Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 1996
Publication Date: N/A
Interpretive Summary: With obesity prevalent and increasing in the United States, there is substantial interest in human energy balance. According to results from the Third National Health and Nutrition Examination Survey (NHANES III), the proportion of overweight Americans has increased from 25% to 33% between 1980 and 1991. At any given time, 33-40% of adult American women and 20-24% of adult American men are attempting weight loss. One negative consequence of weight loss is the depression in resting energy expenditure (REE) which has been observed by many researchers. Since resting energy expenditure accounts for 60% of total energy expenditure, a depression in REE may increase the difficulty of post-obese weight maintenance. In this study we have investigated the mechanism behind the observed depression in REE during weight loss. Several methods for prediction of REE were evaluated, and the role of organ size in depression of REE was investigated. The results of this study support the hypothesis that a reduction in visceral organ mass may account for the depression in REE observed during weight loss. These results will benefit scientists investigating weight loss and post-obese weight maintenance by highlighting physiological consequences of weight loss and suggesting directions for future research to increase the success of weight reduction and post-obese weight maintenance.
Technical Abstract: Many researchers have observed a depression in resting energy expenditure per unit fat-free mass (REE/FFM) occurring with energy deficit in weight reducing individuals, and this depression in REE/FFM has been suggested to indicate metabolic adaption. Because of the potential of metabolic adaption to influence post-obese weight maintenance, the mechanism behind such a depression in REE/FFM is of great interest. Since fat-free mass is not of uniform composition, disproportionate changes in high activity tissues may lead to changes in REE/FFM without metabolic adaption. Such a phenomenon is in accord with animal studies showing a dependence of organ masses on level of food intake. In this study we have used mathematical modeling to investigate the mechanism behind the reduction in REE during weight loss. Several mechanistic and empirical predictions of resting energy expenditure were evaluated. The most accurate prediction of REE was incorporated into a model of total human energy expenditure, and model results were compared to experimental observation. Model results support the hypothesis that decreases in organ size may account for the depression in REE observed during weight loss.