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Whole-grains Improve Insulin Sensitivity in Overweight and Obese Adults

A new Harvard Medical School study shows that even in overweight and obese adults, whole grains improve the body's sensitivity to insulin, the hormone that ushers sugars into cells for use as energy, while refined grains lower the body's sensitivity to insulin.

Epidemiologic studies have found that consumption of whole-grains is associated with a lower risk for type 2 diabetes and heart disease. Now this study shows one reason why: whole grains improve the body's ability to use the carbohydrates they contain, while refined grains lessen the body's ability to burn carbohydrates.

In this study, after estimating total energy needs to maintain subjects' current weight, Harvard researchers gave 11 overweight or obese subjects diets that included 6-10 servings a day of breakfast cereal, bread, rice, pasta, muffins, cookies, and snacks. For one six-week period, subjects received these foods made from whole grains, then for another six-week period, they were given the same foods made from refined grains. After each six-week diet period, subjects were given a liquid mixed meal and their blood samples were taken over a 2 hour period. In contrast to the refined-grain diet, after the whole-grain diet,

The researchers concluded that whole-grain foods' ability to improve insulin sensitivity may be an important mechanism through which whole grains reduce the risk of type 2 diabetes and heart disease.

While diets such as the Atkins diet claim that carbohydrates will make us fat, what this study clearly shows is that refined carbohydrates-not foods made from whole grains-are at fault.

In the U.S., most cereal, bread, pasta, muffins, cookies and snacks are made from refined wheat flour that has been processed into 60% extraction, bleached white flour. 60% extraction-the standard for most wheat products in the United States-means that 40% of the original wheat grain was removed, and only 60% is left. Unfortunately, the 40% that gets removed includes the bran and the germ of the wheat grain-its most nutrient-rich parts. In the process of making 60% extraction flour, over half of the vitamin B1, B2, B3, E, folic acid, calcium, phosphorus, zinc, copper, iron, and fiber are lost.

Since 1941, laws in the United States have required "enrichment" of processed wheat flour with vitamins B1, B2, B3 and iron in response to the problems created by 60% extraction. Since not nearly as much of these B vitamins and iron are replaced as are removed from 60% extraction flour, "enriched" seems an odd word to describe this process.

If you select 100% whole wheat products, however, the bran and the germ of the wheat will remain in your meals, and in addition to improving your insulin sensitivity, the health benefits of whole wheat are impressive! Our food ranking qualified whole wheat (in its original non-enriched form) as a very good source of dietary fiber and manganese, and as a good source of magnesium, vitamin B3, vitamin B5 (pantothenic acid), vitamin B6, iron and protein. Whole wheat also provided smaller amounts of vitamin E, B1, B2, folic acid, calcium, copper, potassium, selenium,and zinc.

To make sure wheat products are made from the whole grain, look for products whose first ingredient is whole wheat. When the first ingredient listed is wheat, this means that the product has been made from refined flour.

To learn more about the numerous health benefits of this whole grain, click wheat.

For information that will help you make whole foods the foundation of your healthy way of eating, click The George Mateljan Healthy Way of Eating.

Reference: Pereira MA, Jacobs DR Jr, Pins JJ, Raatz SK, Gross MD, Slavin JL, Seaquist ER. Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. Am J Clin Nutr 2002 May;75(5):848-55.