Background: The extent and impact of obesity as an isolated risk factor for coronary artery disease is not clear since co-morbidities serve as confounders and may mask this association.

Objectives: To examine whether obesity is associated with extensive coronary artery disease among metabolically healthy patients presenting with ST-elevation myocardial infarction (STEMI) and to explore the outcomes according to body mass index (BMI).

Methods: We stratified STEMI patients who had a metabolically healthy phenotype and available weight and height data according to BMI: 18.5–25 kg/m² (lean), 25.01–30 kg/m² (overweight), and > 30 kg/m² (obese).

Results: Overall 381 patients were included, 42% lean, 41% overweight, and 17% obese. Patients with increased BMIs had higher levels of low-density proteins and triglycerides (P < 0.05). Obese patients presented with the lowest rates of multi-vessel disease (12.9% vs. 22.9% for overweight and 28% for lean). In a univariable analysis, obese patients were 60% less likely to be diagnosed with multi-vessel disease (odds ratio 0.4, 95% confidence interval 0.2–0.9, P = 0.021) compared to lean patients. The association remained significant in a multivariable model adjusted for baseline characteristics (P = 0.029). There were no differences in 30-day or long-term mortality (median follow-up 3.2 years) among the groups (P > 0.1 for all comparisons).

Conclusions: Metabolically healthy phenotype obesity was associated with lower rates of multi-vessel disease despite higher levels of triglycerides. However, this association did not translate into increased mortality.