Genetic factors in obesity.

Several points should be emphasized in summarizing the role of biological inheritance in human body-fat variation. First, at least two kinds of genetic effects must be considered: the additive genetic effect and the genotype-environment interaction effect. Second, from the data reviewed here, we conclude that the additive genetic effect in amount of subcutaneous fat is quite low but that it is higher (around 25 to 30 per cent) for fat mass and regional fat distribution. These results suggest that visceral fat, perhaps, is more influenced by the genotype than subcutaneous fat. Third, it appears that a genotype-overfeeding interaction component exists for body fat, which suggests that sensitivity of individuals to changes in body fat following overfeeding are genotype-dependent. Fourth, the limited data available suggest that the genotype accounts for a significant fraction (equal to or greater than 40 per cent) of the individual differences in RMR, TEM, and TEE. Fifth, one finds a slight genetic effect for the proportion of protein, fat, and carbohydrate in the diet. Sixth, there is some indication that individual differences in habitual physical activity level are characterized by a significant genetic component. The search for genetic markers of the various obesity phenotypes has not been initiated to any extent at this time. However, one can anticipate considerable development in this area in the coming decade.