1. ¹Clinical Endocrinology Branch, NIDDK, Bethesda, Maryland, USA
2. ²Nutrition Department, National Institutes of Health, Bethesda, Maryland, USA
3. ³BioMedical Computer Institute, Philadelphia, Pennsylvania, USA

Correspondence: Anne E. Sumner (AnneS@intra.niddk.nih.gov)

Received 9 September 2007; Accepted 2 January 2008; Published online 21 February 2008.

Abstract

Total body size and central fat distribution are important determinants of insulin resistance. The BMI and waist circumference (WC) thresholds in African Americans that best predict insulin resistance are unknown. Our goal was to determine the BMI and WC values in African Americans, which optimally predict insulin resistance. The subjects were African Americans (68 men, 63 women), aged 35 8 years (mean s.d.), with a BMI of 30.9 7.5, in the range of 18.5–54.7 kg/m², and with a WC of 98 18, in the range of 69–173 cm. Insulin resistance was defined by the lowest tertile of the insulin sensitivity index (S_I). The Youden index was calculated to determine the WC and BMI thresholds that predict insulin resistance with an optimal combination of sensitivity and specificity. In men the thresholds that optimally predicted insulin resistance were a BMI 30 kg/m² or a WC 102 cm. For women, insulin resistance was best predicted by a BMI 32 kg/m² or a WC 98 cm. In African Americans, insulin resistance (in men) was best predicted by a WC 102 cm, and in women by a WC 98 cm, or by a BMI value that fell in the obese category (men: 30 kg/m², women: 32 kg/m²).