Beyond Body Mass Index: Body Roundness Index, Inflammation, and Death.

BACKGROUND: The body mass index (BMI) is widely used to assess obesity but fails to reflect fat distribution. The body roundness index (BRI) has been proposed as a better surrogate for central obesity, yet direct comparisons of their predictive power remain limited. METHODS: We analyzed 341 336 adults from the Taiwan MJ cohort, free of cardiovascular disease at baseline, with a mean follow-up of 19.1 years. Anthropometric, laboratory, and lifestyle data were analyzed to compare the predictive performance of BRI and BMI for all-cause and cardiovascular mortality. Mediation analysis using CRP (C-reactive protein) was conducted to evaluate the role of inflammation in the relationship between these anthropometric indices and death. RESULTS: BRI showed a significant J-shaped association with death, with increased risks at extremes. In multivariable models, BRI outperformed BMI in discriminating all-cause (area under the receiver operating characteristic curve, 70.5% versus 59.3%) and cardiovascular death (area under the receiver operating characteristic curve, 75.4% versus 62.7%). Categorical net reclassification improvement analysis indicated that BRI significantly enhanced risk prediction for all-cause (net reclassification improvement, 44.5%) and cardiovascular death (net reclassification improvement, 30.2%). Crucially, CRP levels mediated 23.9% of BRI's effect on all-cause death and 13.2% on cardiovascular death, while no significant mediation was observed with BMI. CONCLUSIONS: BRI provides superior mortality prediction compared with BMI, likely due to its association with visceral adiposity and inflammation. These findings highlight BRI's potential as a more accurate tool for risk stratification and the importance of targeting inflammation to mitigate obesity-related risks.