New JAMA Study Pinpoints How Mediterranean Diet Reduces Diab
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The known reduction in the risk of type 2 diabetes associated with adoption of the Mediterranean diet appears specifically attributed to its beneficial effects on some key factors, a new study published online in JAMA Network Open reveals.

While a reduction in BMI may be somewhat obvious, other mechanisms include beneficial effects on insulin resistance, lipoprotein metabolism, and inflammation.

However, the diet's antidiabetes effect does not appear to extend to people whose weight is considered healthy (BMI under 25 kg/m2), according to the findings.

Mediterranean Diet Reduced Diabetes Riskin Those With BMI greater than 25 kg/m2:

The Mediterranean diet, with an emphasis on healthy olive oil as the predominant source of oil, favors fruits, vegetables, legumes, nuts, and seeds, fish and dairy products, while limiting intake of red and processed meats as well as sweets.

The diet has been linked to as much as a 25% to 30% reduction in the risk of diabetes in previous observational studies.

To investigate the precise mechanisms that underlie the prevention of diabetes, researchers examined data from 25,317 healthy women participating in the Women's Health Study who had baseline assessments between September 1992 and May 1995. They were a mean age of 52.9 years at baseline. Over the course of the study, 2307 participants developed type 2 diabetes.

With a mean follow-up of 19.8 years, those who had the highest self-reported adherence to the Mediterranean diet (a score greater than 6 on a scale of 0 to 6) at baseline, had as much as a 30% lower risk of developing type 2 diabetes after multivariate adjustments compared to those with a lower Mediterranean diet score.

The diabetes-related biomarkers that contributed the most to the reduced risk were insulin resistance, accounting for 65% of the reduction, followed by BMI (55.5%), high-density lipoprotein measures (53%), and inflammation (52.5%).

Other factors, though to a lesser degree, included branched-chain amino acids (34.5%), very low-density lipoprotein measures (32.0%), low-density lipoprotein measures (31.0%), blood pressure (29.0%), and apolipoproteins (23.5%). Differences in A1c levels only had a limited effect on the risk (2%).

Notably, a subgroup analysis looking at effects of the diet according to baseline BMI showed the reductions in type 2 diabetes associated with higher intake of the Mediterranean diet only extended to those with an above normal weight (BMI greater than 25 kg/m2).

Researchers noted that, as this was not a prespecified analysis, these findings should be viewed as hypothesis-generating, but are consistent with the well-known increase in diabetes risk seen with a higher BMI.

"The finding fits with the biology and pathogenesis of type 2 diabetes that is driven in large part by excess weight, in particular for visceral adiposity and its resulting metabolic dysregulation and inflammation," authors said.

However, the findings suggest that "even a small increase in adherence to the Mediterranean diet has substantial benefits over many years in preventing diabetes, among many other health benefits such as lowering insulin resistance and inflammation, improving lipid metabolism, and lowering blood pressure," they concluded.