Current evidence suggests that such a diet has a protective role in cardiovascular disease, but little is known about its role on the risk of developing diabetes in healthy populations.

The SUN prospective cohort study involved over 13 000 graduates from the University of Navarra in Spain with no history of diabetes, who were recruited between December 1999 and November 2007, and whose dietary habits and health were subsequently tracked.

Participants initially completed a 136 item food frequency questionnaire designed to measure the entire diet. The questionnaire also included questions on the use of fats and oils, cooking methods and dietary supplements.

Every two years participants were sent follow-up questionnaires on diet, lifestyle, risk factors, and medical conditions. New cases of diabetes were confirmed through medical reports.

During the follow-up period (median 4.4 years) the researchers from the University of Navarra found that participants who stuck closely to the diet had a lower risk of diabetes. A high adherence to the diet was associated with an 83% relative reduction in the risk of developing diabetes.

Interestingly, those participants who stuck strictly to the diet also had the highest prevalence of risk factors for diabetes such as older age, a family history of diabetes, and a higher proportion of ex-smokers. This group of participants was therefore expected to have a higher incidence of diabetes, but this was not the case. If fact, say the authors, they had a lower risk of diabetes, suggesting that the diet might provide substantial protection.

The major protective characteristics of the diet include a high intake of fibre and vegetable fat, a low intake of trans fatty acids, and a moderate intake of alcohol. In addition, a key element of the diet is the abundant use of virgin oil for cooking, frying, spreading on bread, and dressing salads.

The authors conclude by calling for larger cohorts and trials to confirm their findings.