A diet high in vegetable fat is superior to a low-fat diet for reducing the risk of cardiovascular disease

February was American Heart Month, and it’s probably no coincidence that it also marked the release of a landmark study from Spain, reporting how a Mediterranean diet supplemented with extra virgin olive oil (EVOO) or nuts markedly reduced the risk of severe cardiovascular events among people with high cardiovascular risk.

Until now, there was little empirical evidence that the Mediterranean diet lowered the risk of cardiovascular disease. It was based predominantly on data reporting that people from Mediterranean countries appeared to have reduced rates of heart disease – a statistic that could be affected by multiple factors in addition to diet. In one of the world’s largest and longest dietary intervention studies, a multicenter, randomized trial in Spain investigated the effect of the Mediterranean diet on cardiovascular risk. They reported their findings in the February 25, 2013 issue of the New England Journal of Medicine.

The results showed that a Mediterranean diet supplemented with either EVOO or nuts reduced the incidence of severe cardiovascular events by up to 30% in participants at high risk of developing heart disease.

Researchers from the Hospital Clinic of Barcelona and the Universidad de Navarra in Pamplona in Spain, randomly assigned 7,447 men and women (age 55-80 years) with no cardiovascular disease but high cardiovascular risk factors (due to overweight or obesity, diabetes mellitus, hypertension, increased low-density lipoprotein cholesterol levels, reduced low-density lipoprotein cholesterol levels, or a family history of coronary heart disease), to one of three diets for five years, starting in October 2003:

  • A Mediterranean diet supplemented with EVOO (at least 4 tablespoons a day)

  • A Mediterranean diet supplemented with nuts (one ounce a day of a combination of walnuts, almonds and hazelnuts)

  • A standard low-fat diet

Participants in the Mediterranean diet groups were also instructed not to reduce calorie intake, but to avoid commercially made cookies, cakes, and pastries, and to limit their intake of processed meats and dairy products. They were required to eat: at least three servings a day of fruits; at least two servings a day of vegetables; fish at least three times a week; legumes (beans, peas and lentils) at least three times a week; white meat instead of red. Those who drank alcohol were also asked to have at least seven glasses of wine a week with meals.

Those in the Mediterranean diet groups additionally attended regular dietary training sessions. Individuals following the low-fat diet, however, received leaflets for the first three years that explained a low-fat diet; at the three-year mark, these participants were then also invited to attend regular dietary training sessions, and received dietary advice at the same intensity level as those in the Mediterranean groups.

The trial was stopped early, at 4.8 years, when it was deemed unethical to continue the study due to the clear benefit demonstrated among participants in the Mediterranean group diets. Compared to the low-fat diet, individuals following the Mediterranean diet with EVOO or nuts were less likely (30% and 28% respectively) to experience a major cardiovascular event (myocardial infarction, stroke, or cardiovascular death).

The researchers reported that individuals stayed with the Mediterranean diet, while participants in the low-fat diet group found compliance difficult, and did not actually reduce their fat intake much. Consequently the trial ended up comparing the Mediterranean diet with the typical modern diet that comprises red meat, processed foods, commercial baked goods, and sodas.

Participants in the low-fat diet group were also twice as likely to drop out of the study, than those following the Mediterranean diets (11.3% vs 4.9%).

The results of this study confirm the benefits of the Mediterranean diet in reducing heart disease. They also support evidence that low-fat diets are not especially beneficial, and are difficult for individuals to maintain. The researchers did report, however, that although the diet reduced the risk of heart disease in individuals at high risk for it, further studies are necessary to determine the benefits of this type of diet in people at low risk of heart disease.