Commentary: Relationship between weight-adjusted waist circumference index and prevalence of gallstones in U.S. adults: a study based on the NHANES 2017-2020

Rui Du Yanfei Yang Qi Zhang Zhikun Lin ^* Shimeng Cui ^* Guang Tan ^*

• Department of General Surgery, The First Affiliated Hospital of Dalian Medical University, Dalian, China

We read with interest the article by Ke et al. entitled "Relationship between weight-adjusted waist circumference index and prevalence of gallstones in U.S. adults: a study based on the NHANES 2017-2020" (1). In this study, the authors investigated the relationship between the weight-adjusted waist circumference index (WWI) and gallstones in the U.S. population using data from National Health and Nutrition Examination Survey (NHANES) 2017-2020. WWI is a new index for assessing obesity, with the advantage of distinguishing body fat from muscle mass compared with traditional ones. A total of 7971 individuals who met the criteria set by the authors participated in this cross-sectional study. The authors first classified the weighted characteristics based on the presence or absence of gallstones and found that patients with gallstones had higher levels of WWI. Subsequently, the authors constructed three multivariate regression models to explore the relationship between WWI and gallstones. Model 1 didn't adjust for covariates, Model 2 adjusted for key demographic variables and Model 3 adjusted for all covariates in the study. Further exploration using generalized additive models and smooth curve fitting revealed a nonlinear positive correlation between WWI and the prevalence of gallstones. The likelihood ratio test revealed a threshold effect of WWI on the prevalence of gallstones with an optimal inflection point value being 10.71. WWI was then converted from a continuous variable to a bicategorical variable, propensity score and inverse probability weighting were used on Model 4 which adjusted for all covariates.Finally, the authors performed subgroup analyses stratified by gender, age and race by using stratified multiple regression analysis and added interaction terms to test the heterogeneity of associations between subgroups, aiming to study the relationship between WWI and gallstones in different populations. The results indicated that higher levels of WWI were associated with higher prevalence of gallstones. This study innovatively and comprehensively analyzed the relationship between WWI and gallstones, suggested that WWI is an effective predictor of gallstones development.However, we have deeper reflections on this study.Firstly, in this study, the authors selected several important covariates, including age, gender, physical activity, etc. In the meanwhile, additionally adjusted for the metabolic score for insulin resistance (METS-IR) index to explore the relationship between insulin resistance and the prevalence of gallstones. These are highly commendable. We noticed that the authors included dietary information as covariates when collecting data. In the logistic regression analysis that followed, Model 3 adjusted for total water, total kcal, total sugar, and total fat. However, these dietary data were not presented in Table 1. The authors also included smoking status as a covariate in this study. Yet, we could not find the ALQ101 questionnaire in NHANES 2017-2020. Therefore, we raise doubts about the scientific validity of this study and hope the authors will provide further explanation. Additionally, Nordestgaard et al.found that high coffee intake is associated observationally with low risk of gallstones (2). Therefore, we hope the authors will include coffee intake as a covariate to better understand if diet mediates the relationship between WWI and gallstones.Secondly, as the relationship between obesity and gallstones has already been studied before (3), could the advantages of WWI in assessing obesity compared with traditional ones be further explained to emphasize the significance of this study? For example, evaluate and compare the predictive ability of WWI and traditional obesity assessment indicators, such as body mass index (BMI), waist circumference (WC) and body weight (BW) for gallstones through receiver operator characteristic curve. This is because WWI is derived from BW and WC. When conducting predictive ability assessments, we believe it should be compared with these two individual body measurement data points, as well as the traditional obesity assessment indicator BMI, to highlight the importance of WWI(4).In conclusion, this study innovatively explores the relationship between WWI and gallstones among the American population. However, we hope the authors can take our questions into account to improve the study and provide additional insights on gallstones in the future.