An L-shaped nonlinear association exists between body roundness index and all-cause mortality in myocardial infarction survivors, with an inflection point at BRI 3.99 below which each 1-unit BRI increase significantly reduced mortality risk (HR=0.62, 95% CI: 0.50-0.75).
The relationship between BRI and all-cause mortality in MI survivors follows an L-shaped nonlinear pattern with an inflection point at BRI 3.99.
Below the BRI threshold of 3.99, each 1-unit increase in BRI was significantly associated with reduced all-cause mortality risk.
Above the BRI threshold of 3.99, BRI showed no statistically significant association with all-cause mortality.
The study cohort consisted of 2099 MI survivors from NHANES 1999-2018 with a median follow-up of approximately 9 years.
Lower BRI was associated with higher all-cause mortality in MI survivors, suggesting maintaining BRI above critical thresholds may confer survival benefits.
This research suggests that the relationship between body shape and survival after a heart attack is more complex than previously assumed. The study used a measure called the Body Roundness Index (BRI), which estimates body fat distribution using waist circumference and height, and tracked nearly 2,100 heart attack survivors from a large U.S. national health survey over roughly 9 years. Rather than finding that a rounder (higher BRI) body shape always worsened survival, the researchers found an L-shaped relationship: people with very low BRI values (below 3.99) had significantly higher death rates, while those above that threshold showed no further change in risk regardless of how much higher their BRI went. Specifically, for every one-unit increase in BRI below the threshold of 3.99, the risk of dying during follow-up was reduced by about 38%. Above that threshold, BRI had essentially no effect on survival risk. This pattern held up when the researchers looked at different subgroups of participants. The BRI threshold of 3.99 therefore appears to represent a critical boundary below which being too lean or having insufficient body fat may be harmful for people who have already had a heart attack. These findings matter because they add to a growing body of evidence around the 'obesity paradox' — the observation that in certain high-risk patient groups, very low body weight or leanness can be associated with worse outcomes rather than better ones. This research suggests that for heart attack survivors specifically, being underweight or having a very low body roundness index may signal nutritional deficiency, muscle loss, or other health vulnerabilities that increase mortality risk. Clinicians caring for heart attack survivors may need to consider whether patients with very low BRI values need nutritional support or monitoring, rather than focusing exclusively on reducing adiposity.
Qin S, Fang Z, Gu T, Hu S, Zhao J, Shao X, et al.. (2026). Nonlinear association between body roundness index and all-cause mortality in myocardial infarction survivors: A cohort study based on NHANES 1999-2018.. Medicine. https://doi.org/10.1097/MD.0000000000050531