There were no data about the influence of fat-free mass (FFM) and body fat (BF) on the prognosis of myocardial infarction (MI) patients. For a study, researchers sought to examine the impact of FFM and BF (calculated using formulas rather than actual measurements) on 30-day and long-term all-cause mortality in MI patients after percutaneous coronary intervention. They examined data from 6,453 MI patients. The patients were classified into 2 groups (high/low) based on the fat-free mass index (FFMI) and 2 groups (low/high) based on the body fat (BF). The resulting 4 patient groups were compared: HighFFMI-LowBF, HighFFMI-HighBF, LowFFMI-LowBF, and LowFFMI-HighBF. The HighFFMI-LowBF group had the lowest 30-day and long-term crude mortality rates (3.0% and 9.8%, respectively), followed by the HighFFMI-HighBF group (6.6% and 27.0%), the LowFFMI-LowBF group (10.4% and 36.0%, respectively), and the LowFFMI-HighBF group (14.7%, 56.8%, respectively). The difference was statistically significant (P<0.0001), as was the distinction between the groups. After adjustment, the FFMI-BF groups predicted 30-day mortality independently (P=0.003), although the risk was comparable across all groups. Long-term mortality risk was similar in the HighFFMI-HighBF group compared to the HighFFMI-LowBF group (hazard ratio [HR] 1.11, 95% CI 0.84 to 1.47, P=0.47). In contrast, the LowFFMI-LowBF and LowFFMI-HighBF groups had a higher risk (HR 1.59, 95% CI 1.20 to 2.11, P=0.001 and HR 1.40, 95% CI 1.03 to 1.91, P=0.033, respectively).  In patients with MI, body composition predicted mortality more accurately than body mass index. Mortality appeared to be inversely proportional to FFM, with individuals with low FFM and low BF having an elevated risk of death. The body composition groups also validated the paradox of obesity.

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