Along with less heart disease and diabetes, a Mediterranean diet is also linked with lower risk for metabolic syndrome, according to a new meta-analysis.
In some populations, the diet also lowered the risk for abdominal obesity, lipid levels, glucose metabolism and blood pressure - that is, the individual components and not just metabolic syndrome overall.
The Mediterranean diet includes an abundance of fruits, vegetables, legumes, nuts, olive oil and fish, with very little red meat. Its benefits are generally attributed to antioxidant and anti-inflammatory effects.
"This study reinforces guidelines over the past 10 years, stressing the need to reduce consumption of refined carbohydrates and saturated fats from animal products," Dr Robert S. Rosenson, director of cardiometabolic disorders at Mount Sinai Medical Centre in New York, told. Dr Rosenson was not involved in the study.
A team of researchers from Greece and Italy, led by Dr Demosthenes B. Panagiotakos at Harokopia University in Athens, identified 50 studies of the Mediterranean diet. Published between 1994 and 2010, the studies involved more than half a million subjects.
Comparators included low-fat or high-carbohydrate diets, usual care, and low adherence to the Mediterranean diet, the investigators say in an online paper in the Journal of the American College of Cardiology.
Eight studies with 10,399 subjects looked particularly at the development or progression of metabolic syndrome; these showed a highly protective effect (log-hazard ratio = -0.69).
Data from 35 trials showed the diet was linked with beneficial mean differences in waist circumference (-0.43 cm), HDL cholesterol (1.17 mg/dL), triglycerides (-6.14 mg/dL), systolic and diastolic blood pressure (-2.35 and -1.58 mm Hg), fasting glucose (-3.89 mg/dL), and Homeostatic Model Assessment insulin resistance (-0.45).
Fifteen observational studies showed significant benefits on HDL cholesterol, triglycerides, glucose and HOMA-IR.
However, the researchers saw significant effects on individual components only in the 35 studies that involved Mediterranean populations. Other trials took place in the US, northern Europe, and Australia.
In sensitivity analyses, only studies with sample sizes above the median (n = 66) showed significant effects of diet on metabolic syndrome components; smaller studies failed to show any significant ties.
In studies that lasted more than 3 months or that encouraged physical activity, all components improved except waist circumference. Shorter duration and lack of physical activity only helped blood pressure and glucose levels.
Dr Robert Eckel of the University of Colorado School of Medicine, a former president of the American Heart Association, told Reuters Health 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."
In other words, he added, "there's nothing really new here."
Dr Eckel raised several issues with the meta-analysis. The comparison diets and other lifestyle modifications were heterogeneous, he said, and "follow-up in the clinical trials varied from 1 month to 5 years - it's hard to make conclusions after 1 month!"
Dr Elizabeth Mayer-Davis, professor of nutrition at the University of North Carolina at Chapel Hill, says it's reasonable to recommend the Mediterranean diet to patients, but for some the higher costs could be a barrier to adopting a diet that emphasises 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/ March 2011)
Go the Mediterranean route