Objective: To review the major data collected over the past 8 yr regarding energy expenditure in relationship to obesity and the development of obesity in the Pima Indian population.
Research design and methods: The different components of 24-h energy expenditure (i.e., the RMR, the thermic effect of food, and the energy cost of spontaneous physical activity) were measured in a respiratory chamber after a few days on a weight-maintenance diet.
Results: Fat-free body mass, the major determinant of RMR, explains 82% of its variance. However, an extra 7% of the variance in RMR observed between people is related to family membership. The variability of RMR for a given body size and composition is of importance, because a low metabolic rate is a major risk factor for weight gain in man. Also, genetic factors seem to be the cause of the familial aggregation of metabolic rate in man.
Conclusions: The high prevalence of obesity and NIDDM in the Pima Indian community might be the consequence of a "thrifty genotype." The increasing evidence that obesity cannot always be attributed to gluttony and sloth forces us to consider obesity as a "real metabolic disease" that needs to be treated as such, using new behavioral and pharmacological therapies.