Metabolic differences and the development of obesity.

Studies, such as those on Pima Indians, have shown that metabolic factors are involved in the development of obesity and that being overweight is not simply a result of "sloth and gluttony." However, the environment also affects the development of obesity. Among individuals in a given environment, the variability in body size is influenced by genetically determined responses to that environment. People with a low metabolic rate (adjusted for body size and composition) are prone to weight gain, whereas those with a high level of spontaneous physical activity are less likely to become obese. Similarly, individuals with a high 24-hour respiratory quotient (RQ) are more likely to gain weight than those with a low RQ. Insulin sensitivity (not insulin resistance) is another metabolic predictor of obesity. Genetic linkage studies suggest a number of genes are linked to the development of obesity. By sibling-pair linkage analysis, tumor necrosis factor-alpha (TNF-alpha) was found to be linked to the percentage of body fat, and other studies have shown that fat cell production of TNF-alpha is greater in obese individuals.