Insulin resistance and weight gain in postmenopausal women of diverse ethnic groups

OBJECTIVE: This study was conducted to examine the influence of insulin resistance on weight change in postmenopausal women of various ethnic groups. SUBJECTS: Data were obtained from 3389 women (60% White, 20% Black, 12% Hispanic, and 8% Asian/Pacific Islander), ages 50 - 79, enrolled in either the Women's Health Initiative Clinical trial or Observational Study, whose blood samples were selected randomly from the full cohort of 161 809 women for analyses. MEASUREMENTS: Glucose, insulin, and lipids were measured on fasting serum samples drawn at baseline and after 3 y of follow-up. Weight, height, waist circumference, and blood pressure were measured. Physical activity and energy intake were assessed via questionnaire. Insulin resistance was estimated using the HOMA (homeostasis model) calculation. RESULTS: Average age was 62 y, average BMI (body mass index) was 27.4 kg/m(2), and average weight change was a gain of 0.4 kg in 3 y. In a multivariate analysis, insulin resistance and insulin concentrations were independent predictors of increases in weight in White women ( P = 0.002 and 0.004, respectively) and in the combined group ( P = 0.027 and 0.039). For the whole group, after adjustment for other covariates, those in the highest quartile of insulin resistance gained 0.4 kg in 3 y, whereas those in the lowest quartile lost 0.06 kg. Similar trends were found for insulin resistance and weight gain in Hispanic and Asian/Pacific Islander women, but they did not reach statistical significance. In Black women, no relation was seen between either insulin or insulin resistance and weight change. A significant interaction between obesity and insulin resistance was observed ( P = 0.002 for White women and 0.032 for the whole group), so that there is weight gain with increasing insulin resistance in the leaner women, but weight loss with increasing insulin resistance in the most obese. CONCLUSION: Insulin resistance appears to be a predictor of weight gain in postmenopausal women, except for the most obese women. The effect is more pronounced in women who have a lower BMI, and the effect was not seen in the Black women who as a group had a higher BMI.