No effect of the Trp64Arg [beta ] 3-adrenoceptor gene variant on weight loss, body composition, or energy expenditure in obese, caucasian postmenopausal women

Abstract

The Trp64Arg polymorphism in the [beta ] 3-adrenoceptor gene has been associated with increased prevalence of obesity, type 2 diabetes, and low rates of energy expenditure, although these findings are not unanimous. It is currently unknown if the presence of the Trp64Arg gene variant impedes the loss of body weight in obese, postmenopausal women via a reducing effect on energy expenditure. The objective of this study was to compare body composition and energy expenditure in carriers and noncarriers of the Trp64Arg variant in the [beta ] 3-adrenoceptor before and after weight loss. We measured body composition, total daily energy expenditure (TEE), resting metabolic rate (RMR), physical activity energy expenditure (PAEE), thermic effect of feeding (TEF), and respiratory quotient (RQ) in 34 obese, postmenopausal women (19 carriers and 15 noncarriers for the Trp64Arg variant) before and after a weight loss intervention. There were no differences in body composition or daily energy expenditure and its components between the 2 groups at baseline. There were significant reductions in body mass, body mass index (BMI), percent body fat, fat-free mass, and fat mass (main effect, all P [lt ] .0001) when analyzed with the 2 genotypes combined, but no significant differences between carriers and noncarriers with respect to change in these variables (group [times ] time interaction term, all P [gt ] .05). Total energy expenditure tended to be reduced (490 kJ [middot] d [minus ]1, P = .13) in both groups following weight loss, but there was no significant group [times ] time interaction term ( P = .78), indicating no difference in the response of the 2 genotypes. There was a 9% reduction in RMR (611 kJ [middot] d [minus ]1, P [lt ] .001) when both groups were considered together, but no significant group [times ] time interaction term ( P = .84), suggesting that both groups responded in a similar manner to the weight loss intervention. PAEE and the TEF were not different following weight loss (both P [gt ] .60). There was a trend for RQ to be reduced after weight loss ( P = .07), but there was no difference between carriers or noncarriers of the Trp64Arg variant ( P = .58). In summary, we found that obese postmenopausal women who carry the Trp64Arg variant in the [beta ] 3-adrenoceptor had similar changes in body composition and energy expenditure to noncarriers of the variant in response to prolonged caloric restriction. These results suggest that the presence of the Trp64Arg variant in the [beta ] 3-adrenoceptor should not be a hindrance to weight reduction.