For people with metabolic syndrome, a Mediterranean diet supplemented with extra-virgin olive oil or nuts may help reverse the condition, according to findings from a clinical trial published in the Canadian Medical Association Journal (CMAJ).

About 25% of adults around the world have metabolic syndrome. The syndrome exists in the presence of three or more factors such as large waist circumference, high blood pressure, low HDL-cholesterol, high levels of triglycerides and high blood sugar concentrations that can increase the risk of diabetes, heart disease and death.

Spanish researchers analyzed data from the PREDIMED randomized controlled trial, which included men and women aged 55–80 years old at high risk of heart disease. Participants were randomly assigned to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with nuts or a low-fat diet as the control. In this secondary analysis, the research team looked at the long-term effects of the Mediterranean diet on metabolic syndrome in 5,801 people. Almost 64% (3,707) of the participants had metabolic syndrome at the start of the study.

After a median follow up period of 4.8 years, the researchers found that people in the two Mediterranean diet groups decreased their central obesity and blood glucose levels and 958 participants (28.2%) no longer met the criteria of metabolic syndrome.

“In this large, multicenter, randomized clinical trial involving people with high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil was associated with a smaller increase in the prevalence of metabolic syndrome compared with advice on following a low-fat diet,” wrote Dr. Jordi Salas-Salvadó, Human Nutrition Unit, Faculty of Medicine and Health Sciences, Universitat Rovira i Virgili and Hospital Universitari de Sant Joan de Reus, IISPV, Reus, Spain, with coauthors.

“Because there were no between-group differences in weight loss or energy expenditure, the change is likely attributable to the difference in dietary patterns.”

However, the Mediterranean diets did not appear to have an effect on the number of new cases of metabolic syndrome, a finding inconsistent with some previous studies.

“Mediterranean diets supplemented with olive oil or nuts were not associated with a reduced incidence of metabolic syndrome compared with a low-fat diet; however, both diets were associated with a significant rate of reversion of metabolic syndrome,” the authors state.