Determinants of insulin-resistant phenotypes in normal-weight and obese black African women

Objective: Subsets of metabolically "healthy obese" and "at-risk" normal-weight individuals have been previously identified. The aim of this study was to explore the determinants of these phenotypes in black South African (SA) women. Methods and Procedures: From a total of 103 normal-weight (BMI <= 25 kg/m(2)) and 122 obese (BMI >= 30 kg/m(2)) black SA women, body composition, fat distribution, blood pressure, fasting glucose levels, insulin resistance, and lipid profiles were measured. Questionnaires relating to family history, physical activity energy expenditure (PAEE), and socio-demographic variables were administered. The subjects were classified as insulin sensitive or insulin resistant according to the homeostasis model assessment of insulin resistance (HOMA-IR) (>= 1.95 insulin resistant). Results: Our study showed that 22% of the normal-weight women were insulin resistant and 38% of the obese women were insulin sensitive. Increased visceral adipose tissue (VAT) (P = 0.001) and decreased VAT/leg fat mass (P <= 0.001), independent of total body fatness, distinguished between the phenotypes. Moreover, the insulin-sensitive women were of higher socioeconomic status, did more leisure and vigorous PAEE and were less likely to use injectable contraceptives. Using a regression model, body fat distribution, percent body fat, age, log leisure PAEE, and use of injected contraception accounted for 35% of the variance in HOMA-IR in the normal-weight women. In the obese women, 34% of the variance in HOMA-IR was explained by the same variables, excluding PAEE. No differences in smoking status or family history of metabolic disease were found between the phenotypes. Discussion: Central fat distribution, total adiposity, socioeconomic status, leisure PAEE, and use of injectable contraceptives distinguished between insulin-sensitive and insulin-resistant black SA women.