To investigate, researchers followed more than 400 initially diabetes-free adults between the ages of 55 and 80. Each had at least three risk factors for heart disease, such as high blood pressure, smoking or excess weight.
At the outset, the men and women were randomly assigned to follow one of three diets: a traditional Mediterranean diet with added emphasis on boosting consumption of olive oil, a rich source of monounsaturated fat; the same diet, with a focus on getting polyunsaturated fats from nuts; or a low-fat diet that encouraged cutting down on all types of fat.
In addition, participants in the olive-oil group were given a free allotment of the oil (a liter per week), and those in the nut group were given enough mixed nuts to have about an ounce per day.
None of the groups were told to limit calories or get more exercise.
Over the next four years, the researchers found 10 percent of participants in the two Mediterranean groups developed diabetes. That compared with 18 percent of those in the low-fat diet group.
When the researchers accounted for a number of other factors, such as participants' weight, smoking history and reported exercise levels, the Mediterranean diet itself was linked to 52 percent reduction in diabetes risk compared with the low-fat diet.
The traditional Mediterranean diet is generally high in vegetables, fiber-rich grains, legumes, fish and plant-based sources of unsaturated fat -- particularly olive oil and nuts -- while being low in red meat and high-fat dairy, prime sources of saturated fat.
The findings were reported in the journal Diabetes Care.
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