Objectives: We assessed the association among ultrasonographically detected non-alcoholic fatty liver disease (US-NAFLD), metabolic syndrome (MetS), and insulin resistance (IR) in non-obese, non-diabetic middle-aged adults, to find out whether US-NAFLD is independently associated with IR in this population.
Methods: A total of 5,878 non-obese (body mass index, ≥ 18.5 and < 25), non-diabetic individuals were analyzed. IR was estimated with the homeostasis model assessment index (HOMA2-IR) and defined when HOMA2-IR ≥ 1.5. MetS was defined by the Adult Treatment Panel III (ATP III) criteria.
Results: MetS was present in 381 (6.5%) participants, IR was present in 801 (13.6%) participants, and US-NAFLD was present in 1,611 (27.4%) participants. The increase in the prevalence of US-NAFLD closely followed the increase in the number of metabolic components diagnosed according to the ATP III criteria (15.2%, 28.5%, 48.0%, 65.7%, 71.4%, and 100% for 0, 1, 2, 3, 4, and 5 metabolic components, respectively, P < 0.001). US-NAFLD showed a significantly higher odds ratio (OR) for IR, regardless of the number of metabolic components (OR (95% confidence interval) of 3.48 (2.45-4.94), 3.63 (2.74-4.82), 3.19 (2.29-4.44), and 2.43 (1.43-3.81) for 0, 1, 2, and ≥ 3 metabolic components, respectively, P < 0.001 for all values). MetS showed a low sensitivity (0.22) for the identification of individuals with IR, and either US-NAFLD alone (0.60) or US-NAFLD with MetS (0.66) improved sensitivity with acceptable trade-off in specificity.
Conclusions: US-NAFLD was an independent predictor for IR, irrespective of the number of metabolic components of MetS in the non-obese, non-diabetic middle-aged Asian adults. US-NAFLD could identify individuals with IR that cannot be identified by MetS in this population.