Non-linear association between metabolic score for insulin resistance and nonalcoholic fatty liver disease: analysis of US National health and nutrition examination survey data, 2017-2020.

Background: Although the metabolic score for insulin resistance (METS-IR) is significantly associated with metabolic disorders, its dose-response relationship with nonalcoholic fatty liver disease (NAFLD) remains inconclusive. This study aimed to investigate the dose-response relationship between the metabolic score for insulin resistance and NAFLD, and to identify its inflection point.

Methods: This cross-sectional study evaluated the association between METS-IR and NAFLD using multivariable logistic regression applied to data from the 2017-2020 US National Health and Nutrition Examination Survey. Non-linear dynamics were investigated through smoothing spline models and segmented regression. Subgroup comparisons were performed, and diagnostic accuracy was assessed using interaction tests and receiver operating characteristic (ROC) analysis.

Results: Among 2,486 eligible participants, 804 (32.34%) were diagnosed with NAFLD. Adjusted regression models revealed a 7% increase in NAFLD likelihood per unit rise in METS-IR (odds ratio [OR] = 1.07, 95% confidence interval [CI]: 1.04-1.10; P < 0.001). Non-linear modeling identified a saturation effect with an inflection point at 46.73 units. Subgroup stratification demonstrated consistent associations across demographic categories (P > 0.05). The diagnostic performance analysis yielded an area under the curve value of 0.861 in the fully adjusted models.

Conclusions: The results of this study confirmed a non-linear dose-response association between METS-IR and NAFLD. Determining the METS-IR may enhance the identification of early-stage NAFLD in clinical and public health settings.