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Background The association between body weight and clinical prognosis in patients with coronary artery disease (CAD) have not been defmitely proved.We conducted a meta-analysis to determine the extent and nature of this association.Methods Major electronic information sources were searched for studies that provided risk estimates for clinical events on the basis of body mass index (BMI) in patients with CAD, and with at least 6 months follow-up.CAD was defined as history of revascularization, myocardial infarction or angina.We obtained risk estimates for five predetermined bodyweight groups: low, normal weight (reference), overweight, obese, and severely obese.Results Data from 292,896 patients in 54 studies were included.The association between body weight and mortality was found a J shape curve.Compared with normal weight group, overweight group has the lowest relative risk (RR) for mortality (RR=0.83, 95% CI 0.79-0.88).The low weight and severely obese patients have the highest RRs (low: RR=1.40, 95% CI 1.30-1.52; severely obese: RR=1.23, 95% CI 1.12-1.35).Mild obese patients have insignificantly lower RR for mortality (RR=0.95, 95% CI 0.87-1.05) but significantly increased RR for cardiovascular events (RR=1.18, 95% CI 1.03-1.34) compared with normal weight patients.Conclusions The better outcomes for cardiovascular and total mortality seen in the overweight and mildly obese groups could not be explained by adjustment for confounding factors.These findings could be explained by the lack of discriminatory power of BMI to differentiate between body fat and lean mass.