The Mediterranean diet doesn't just protect against heart disease: It may actually reverse metabolic syndrome, a cluster of symptoms linked to heart disease and diabetes.
The findings came from a study conducted by researchers from the Universitat Rovira i Virgili and the Hospital Universitari de Sant Joan de Reus in Reus, Spain.
"In this large, multicentre, 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," the researchers wrote.
"Because there were no between-group differences in weight loss or energy expenditure, the change is likely attributable to the difference in dietary patterns."
A heart-healthy diet
Metabolic syndrome refers to a cluster of symptoms that is associated with a higher risk of diabetes, cardiovascular disease and premature death, and affects about 25 percent of all adults globally. The condition can be diagnosed in anyone who has three or more symptoms. Symptoms include high blood sugar, high triglycerides, low HDL ("good") cholesterol, high blood pressure and central obesity (a large waist circumference).
The researchers wondered how the Mediterranean diet could affect metabolic syndrome, because the diet has previously been shown to reduce the risk of cardiovascular disease and type 2 diabetes, as well as lead to better health, longer life and less age-related cognitive decline. For example, a 2013 study published in the New England Journal of Medicine found that people who ate a Mediterranean diet were about 30 percent less likely to develop cardiovascular disease than people who ate a low-fat diet.
The Mediterranean diet has high quantities of olive oil, seeds and nuts, whole grains and beans; moderate to high quantities of dairy, primarily in the form of yogurt and cheese; moderate quantities of fish and poultry; low to moderate consumption of red wine; and low consumption of red meat.
Metabolic syndrome decreased 30 percent
In the new study, researchers randomly assigned 5,801 adults between the ages of 55 and 80 who were considered at high risk of developing heart disease to follow one of three diets: a low-fat diet (control group), a Mediterranean diet plus extra olive oil or a Mediterranean diet plus extra nuts. Participants were followed for an average of 4.8 years.
By the end of the study, there was no difference between the three groups in the numbers who had developed new cases of metabolic syndrome. This showed that, despite being higher in fat, the Mediterranean diet did not worsen metabolic outcomes.
The more surprising outcome came among patients who already had metabolic syndrome at the beginning of the study. Among the groups on one of the two Mediterranean diets, the incidence of metabolic syndrome actually fell by 28.2 percent. Participants receiving extra olive oil were more likely to see decreases in central obesity and blood sugar, whereas participants receiving extra nuts were more likely to see a decrease in central obesity alone.
"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 researchers wrote.
Increasingly, research is suggesting that the benefits of the Mediterranean diet also extend far beyond metabolic health. In a 2010 study conducted by researchers from the University of Navarra in Pamplona, Spain. The Mediterranean diet was found to lower the risk of developing depression by 30 percent -- even after researchers controlled for risk factors including anxiety, personality, lifestyle habits and family status.