The Mediterranean diet includes an abundance of fruits, vegetables, beans, nuts, olive oil, poultry and fish, with very little red meat. Scientists believe that eating this way has antioxidant and anti-inflammatory effects on the body.
"This study reinforces guidelines over the past 10 years, stressing the need to reduce consumption of refined carbohydrates and saturated fats" from meat and dairy products, Dr. Robert S. Rosenson of the Mount Sinai School of Medicine in New York told Reuters Health. He was not involved in the work.
Metabolic syndrome is a recent catchall for unhealthy traits that spell bad news for the heart, such as belly fat, high blood pressure, low levels of "good" HDL cholesterol, elevated fat levels in the blood (triglycerides), and high blood sugar. The condition is diagnosed when a person has at least three of those risk factors.
Reviewing 35 clinical trials, Dr. Demosthenes B. Panagiotakos at Harokopia University in Athens, Greece, and his team found that faithfully eating a Mediterranean diet can improve each of those traits.
For instance, those who stuck with the Mediterranean diet as compared to eating their regular foods or a low-fat diet trimmed their waistlines by about 0.43 cm (0.16 inches) on average.
They also showed slashed their blood pressure by 2.35 points on the top reading, and their fasting blood sugar by 3.89 milligrams per deciliter.
While these benefits may seem small, Dr. Elizabeth Mayer-Davis, who was not involved in the research, said they show a Mediterranean diet might be beneficial.
"So it's reasonable to recommend the Mediterranean diet to patients," she said. But she added that "we can't say that this diet reduces the risk of diabetes."
Nor does the study, published in Journal of the American College of Cardiology, show that the diet cuts the risk of death from heart disease, which has been linked to metabolic syndrome.
Mayer-Davis, professor of nutrition at the University of North Carolina at Chapel Hill, also said she was concerned that cost could be a barrier to adopting a diet that emphasizes fresh foods, olive oil and fish.
"This speaks to the need to improve availability of these kinds of foods to people who don't have a lot of extra money to spend," she told Reuters Health.
Olive oil is an important part of the Mediterranean diet because it is a so-called monounsaturated fat, which "protects" levels of HDL cholesterol.
However, it can cost a lot more than other cooking oils on supermarket shelves. Rosenson said that when he suggests this diet to his patients, he makes the point that the much cheaper canola oil is also high in monounsaturated fats.
Dr. Robert Eckel, a former president of the American Heart Association who reviewed the study for Reuters Health, noted that the Mediterranean diet "is part of a dietary pattern consistent with guidelines from the AHA, the USDA, and other bodies, that overall is consistent with reduced risk for cardiovascular disease, stroke and diabetes."