Both body roundness index and the body mass index increase the prevalence of stroke but reduce the risk of all-cause mortality.

Background and objective: Obesity is a risk factor for stroke. The Body Roundness Index (BRI) is a new obesity indicator based on the eccentricity theory and combined with height and waist circumference, which reflects the level of visceral fat more accurately than traditional indicators. However, its association with stroke remains unclear. This study aims to compare the associations of the BRI and body mass index (BMI) with stroke and its prognosis.

Methods: The data of 29,745 participants in the National Health and Nutrition Examination Survey (NHANES) from 2003 to 2018 were analyzed. Based on weighted logistic regression, weighted COX regression, and restricted cubic spline, the associations of BRI and BMI with the odds of stroke and the risk of all-cause mortality were analyzed; the receiver operating characteristic (ROC) curve and concordance index were used to evaluate the performance of BRI and BMI in predicting stroke and Survival outcome.

Results: After adjusting for all confounding factors, weighted logistic regression and weighted Cox regression respectively showed that both BRI (odds ratio [OR]: 1.06, 95% confidence interval [CI]: 1.02-1.10, P = 0.004) and BMI (OR: 1.01, 95%CI 1.00-1.03, P = 0.03) were independently and positively associated with stroke. Meanwhile, both BRI (hazard ratio [HR]: 0.91, 95%CI 0.86-0.98, P = 0.01) and BMI (HR: 0.95, 95%CI 0.92-0.97, P < 0.0001) significantly reduced the risk of all-cause mortality among stroke survivors. The receiver operating characteristic (ROC) curve showed that the area under the curve (AUC) of BRI for predicting stroke was 0.62, while that of BMI was 0.545, and the difference between the two was significant (P_DeLong < 0.001). The time-dependent c-index curve demonstrated that BRI and BMI had comparable abilities to predict the risk of all-cause mortality among stroke survivors.

Conclusion: Both the BRI and the BMI have verified the obesity and stroke paradox. BRI and the BMI are significantly positively correlated with stroke, and the BRI has a stronger ability to predict stroke than the BMI; however, both the BRI and the BMI are significantly negatively correlated with the prognosis of stroke survivors and have comparable predictive abilities.