“Whole-grain foods are important in diabetes prevention.” That’s the explicit conclusion of both a large-scale prospective study and the implied conclusion of a meta-analysis of earlier trials.

In the first study, 25,067 people aged 35-65 were recruited from the general population of Potsdam, Germany. Each had an examination, was interviewed, and answered a detailed diet questionnaire. During the next nine years, they responded to repeat questionnaires so their diets could be tracked and new cases of diabetes identified. A report of diabetes was confirmed by contacting the person’s clinician.

The 844 people who developed diabetes were divided into five groups based on fiber intake. Those who consumed the most fiber (an average of 16.6 g/day) had a 27% lower risk of developing diabetes than those who ate the least (an average of 7 g/day), even after accounting for different lifestyle risk factors. Whole-grain bread and muesli (a cereal of oats, nuts, and fruit) were the main fiber sources. Surprisingly, fruit and vegetable fiber had no effect (Arch Intern Med. 2007;167:956-965).

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The results were confirmed in an accompanying meta-analysis of nine U.S. and foreign studies. Cumulatively, high cereal-fiber intake produced a 33% decline in diabetes risk. Wheat and corn are the most common sources of whole grain in the American diet, but rye bread may have an additional benefit, resulting in a lower postprandial insulin response compared with wheat bread, independent of its fiber content, the researchers said.