Correlation of the body roundness index (BRI) with chronic diarrhea and chronic constipation: Findings based on the National Health and Nutrition Examination Survey (NHANES) 2005–2010 data

Aim The study aimed to explore potential links between long-term digestive issues (specifically diarrhea and constipation) and BRI in a representative U.S. population sample. Methods This study adopted a design that is cross sectional, drawing on data from the NHANES, gathered from 2005 to 2010. This comprehensive dataset included health information from a total of 11,235 individuals, providing a robust sample for the analysis. Persistent bowel movement patterns were categorized based on the BSFS—Bristol Stool Form Scale, a widely recognized diagnostic tool. Within this framework, stool types 1 and 2 were designated as indicators of long-term constipation, while types 6 and 7 were identified as markers of persistent diarrhea. To assess the relationship between digestive health and the BRI, this study employed weighted logistic regression analysis. To capture and visualize the nuanced interplay between BRI and gastrointestinal patterns, we utilized advanced nonlinear regression methods, specifically restricted cubic spline (RCS) analyses. Additionally, the research compared the efficacy of various physical measurements—including BRI, WC, BMI (body roundness index, waist circumference, and body mass index, respectively)—to determine their respective predictive power for chronic diarrhea and constipation through comparative analysis of receiver operating characteristic (ROC) curves. Results After comprehensive adjustment in the final statistical model (Model 3), the BRI demonstrated a statistically significant association with diarrhea (odds ratio, OR, of 1.24; 95% confidence interval, CI, ranging from 1.08 to 1.43, with P value of 0.004) However, the association between BRI and persistent constipation was statistically insignificant (OR of 1.13, 95% CI ranging from 0.99 to 1.29, P value of 0.060). Nonlinear regression analysis using RCS analysis further uncovered statistically significant nonlinear positive correlations between BRI and both chronic gastrointestinal conditions. The non-linearity was particularly pronounced for diarrhea ( P  = 0.005) and also notable for constipation ( P  = 0.037). Further stratified analyses provided additional insights into specific population subsets. The relationship between BRI and persistent diarrhea was particularly evident among individuals with diabetes. In contrast, the correlation between BRI and constipation was stronger in individuals under 60 years of age. ROC analysis indicated that BRI outperformed conventional anthropometric measures (AUC, area under the curve: 0.601). Specifically, BMI, the body mass index, resulted in an AUC of 0.569, while WC produced an AUC of 0.572. However, the AUC value of BRI (0.537) was less effective than BMI (0.551) and WC (0.570) in diagnosing constipation. Conclusions BRI is closely associated with changes in the individual’s bowel habits, particularly in predicting chronic diarrhea. This study highlighted the potential importance of maintaining moderate BRI levels to improve bowel health and prevent disorders like diarrhea.