Conclusions : Obesity is associated with lower risks after cardiac surgery , with consistent effects noted in multiple analyses attempting to address residual confounding and reverse causation
Background : In an apparent paradox , morbidity and mortality are lower in obese patients undergoing cardiac surgery  , although the nature of this association is unclear .
We sought to determine whether the obesity paradox observed in cardiac surgery is attributable to reverse epidemiology , bias , or confounding .
Relationship of body mass index with outcomes after coronary artery bypass graft surgery.
BACKGROUND A debate exists whether obesity is a risk factor for operative mortality after  coronary artery bypass graft surgery ( CABG ) . The contradictory findings in the literature may largely be attributable to the variety of method ological approaches used to model the association between body mass index ( BMI ) and post-CABG outcomes . This study aims to investigate this association , and to uncover possible explanations for the lack of consensus across prior studies . METHODS Data were prospect ively collected on 80,792 patients who underwent a CABG procedure during a 14-year period at the 45 Department of Veterans Affairs cardiac surgery programs .  Generalized additive models were used to estimate the relationship of BMI and outcomes after a CABG procedure . RESULTS We found that the relationship of BMI with post-CABG mortality and morbidity is U-shaped with the minimum risk located around a BMI of 30 kg/m2 , indicating that patients classified as overweight have the lowest risk , and those in the lower end of the obese range do not have seriously elevated risk . This U-shape relationship is significantly nonlinear and robust to adjustment for other risk factors . CONCLUSIONS This study demonstrates that BMI is an independent predictor of mortality and morbidity after CABG surgery . Previous studies that model BMI linearly or as categories can not accurately capture this U-shaped relationship and are unlikely to find a significant contribution by including BMI . Further research is needed to determine the mechanisms of risk for patients with low and high BMI and whether interventions to modify BMI may improve patient outcomes
Conclusions : Obesity is associated with lower risks after cardiac surgery , with consistent effects noted in multiple analyses attempting to address residual confounding and reverse causation
Background : In an apparent paradox , morbidity and mortality are lower in obese patients undergoing cardiac surgery  , although the nature of this association is unclear .
We sought to determine whether the obesity paradox observed in cardiac surgery is attributable to reverse epidemiology , bias , or confounding .