Insulin resistance is not necessarily an essential element of metabolic syndrome.

Type 2 diabetes is frequently associated with metabolic syndrome (MetS). Insulin resistance (IR) is thought to be the underlying pathophysiology of MetS. The purpose of this study is to examine the association of MetS with IR and beta cell function. This is a cross-sectional study in NHANES 1999-2000 participants who were at least 18 years old, including 911 non-Hispanic whites (NHW), 398 non-Hispanic blacks (NHB), and 595 Mexican-Americans (MA). MetS was defined based on the revised ATP III. IR and beta cell function were calculated using homeostasis model assessment (HOMA-IR and HOMA-B). The high-risk tertile was defined as the highest HOMA-IR and lowest HOMA-B. The odds ratio (OR) was calculated against the other two tertiles. The relationship of HOAM-IR and HOMA-B with the components of MetS was also examined. IR was a risk factor of MetS in all three ethnic groups (OR 4.17-12.01, P < 0.0001). Fasting glucose, triglycerides, and HDL cholesterol were associated with IR (P < 0.001) and correlated with HOMA-IR (P < 0.001), while inconsistent results were noted in blood pressure and waist circumference among three racial/ethnic groups. However, in the MetS subjects, 32 % of NHW, 28 % of NHB, and 44 % of MA were not in the IR tertile and in the IR subjects, 25 % of NHW, 36 % NHB, and 30 % of MA did not have MetS. No relationship was found between beta cell function and MetS. Although IR is a risk factor for MetS, IR is neither necessary nor required for MetS.