Association between relative fat mass and gallstones: a cross-sectional study based on NHANES 2017-2020.

Background: Gallstones are a common gastrointestinal disease worldwide, associated with significant public health burdens. Obesity and fat distribution are recognized as major risk factors for gallstone formation, yet traditional anthropometric indices such as BMI and WC have limitations in reflecting fat distribution and its metabolic consequences. Relative Fat Mass (RFM), a novel anthropometric index, may provide more accurate predictions of gallstone risk, but its association with gallstone formation remains underexplored. Methods: This study utilized data from NHANES 2017-2020, including 6,084 participants aged ≥20 years, to investigate the relationship between RFM and gallstone risk. Multivariable logistic regression and smooth curve fitting were used to assess this association. RFM's predictive ability was compared with traditional indices using ROC and decision curve analysis (DCA). LASSO regression and AIC-based multivariable regression were employed to construct a gallstone risk prediction model. Results: Each one-unit increase in RFM was associated with a 11% higher risk of gallstones (OR: 1.11; 95% CI: 1.08-1.13). The smooth curve fitting revealed a linear relationship between RFM and gallstones. RFM demonstrated superior predictive ability (AUC = 0.705) compared to BMI, WC, WWI, and BRI. The predictive model, incorporating age, RFM, diabetes, waist circumference, and alcohol consumption, achieved good performance (AUC = 0.738) with sensitivity and specificity of 70 and 66%, respectively. Conclusion: RFM is strongly associated with gallstone risk and outperforms traditional anthropometric measures in risk prediction. The study presents a model that serves as a useful instrument for recognizing populations at elevated risk and facilitating focused interventions, especially among those with a prevalent occurrence of obesity and metabolic disturbances. These findings support the potential of RFM as an effective measure in clinical and public health settings for reducing the burden of gallstone-related diseases.