Background: Obesity is a coronary disease risk factor demonstrating inconsistent effects on acute coronary syndrome (ACS) outcome.

Methods: To explore the association of body mass index (BMI) and clinical outcome in ACS patients, we analyzed data of 5751 ACS patients (77% males) from the Acute Coronary Syndrome Israel Survey between March and April during 2002, 2004 and 2006.

Results: Patients were divided into 4 National Institutes of Health, BMI-based categories: underweight (BMI < 18.5 kg/m², n = 43); normal (BMI = 18.5–24.9 kg/m², n = 1709); overweight (BMI = 25.0–29.9 kg/m², n = 2700); obese (BMI ⩾ 30 kg/m², n = 1299). Mean BMI increased significantly in ACS patients from 2002 to 2006. Time from chest pain onset to hospitalization and invasive procedure, Killip class on admission, left ventricular ejection fraction, creatinine clearance and in-hospital therapy were similar in all four groups. Obese and overweight patients were significantly younger than underweight and normal patients (61.4 ± 12.4 and 63.3 ± 12.6 years vs. 69.9 ± 17.7 and 65.3 ± 13.7 years respectively, p for trend < 0.0001). After multivariable adjustment, overweight patients had the lowest 30-day and 1-year mortality [adjusted odds ratio (OR) 0.52, 95% confidence interval (CI) 0.39–0.68 and hazard ratio (HR) 0.65, 95% CI 0.54–0.78, respectively] followed by obese [OR 0.92, 95% CI 0.66–1.28 and HR 0.91, 95% CI 0.73–1.13], normal [1.0 and 1.0] and underweight patients [1.64, 95% CI 0.59–4.61 and 1.39, 95% CI 0.73–2.63].

Conclusion: Overweight and obese ACS patients were younger with a better survival rate than normal and underweight patients. Our observation of a U-shaped relationship between increasing BMI and mortality in ACS patients warrants cautious prospective evaluation.