In the early 1970s, accumulating evidence showed remarkably low rates of coronary heart disease in various Mediterranean countries, where fat consumption was fairly high but olive oil was the dominant source of dietary fat.1 Prospective cohort studies corroborated and extended those findings by showing that polyunsaturated and monounsaturated fats decrease the risk of coronary heart disease, whereas trans fats and saturated fats increase risk.

Despite much research into the relation between dietary fat and coronary heart disease in recent decades, no prospective study has comprehensively investigated the association between consumption of fried food and subsequent risk of coronary heart disease. The linked prospective cohort study by Guallar-Castillón (doi:10.1136/bmj.e363) and colleagues fills this gap.2 The study comprised 40 757 people (about two thirds of whom were women) and was conducted in five regions in Spain that traditionally have widely varying diets. Participants were interviewed at baseline (1992) about their usual diet and food preparation. Sixty two per cent of study subjects reported using olive oil for frying and the remaining participants …