Researchers from Harvard University followed almost 8,000 nurses with type 2 diabetes for almost three decades.
They found that women who ate the most bran had a 35% lower risk of death from heart disease and a 28% lower risk of death from all causes than women who ate the least.
The new research suggests eating a balanced diet that includes complex carbohydrates in the form of whole grains can help lower this risk, American Heart Association spokesman Robert Eckel, MD, tells WebMD.
Eckel is a professor of medicine at the University of Colorado in Denver.
"Many diabetics still believe they should limit carbohydrates, including complex carbohydrates," he says. "Certainly refined grains and simple sugars raise blood sugar and should be limited. But it looks like eating whole grains is not only safe, but beneficial."
Anatomy of a Grain
An unrefined grain of wheat, rice, oat, corn, or any other cereal contains three parts: the tough outer bran layer, the middle endosperm, and the inner kernel or germ.
The fiber in grain is found in the bran, while bran and germ contain most of its vitamins and minerals.
Refined grain products, such as white flour and white rice, contain only the starchy endosperm. B vitamins and iron, but not fiber, are usually added back after processing.
In the newly published investigation, researchers examined data from the ongoing Nurses Health Study, which is one of the largest and most detailed studies of women's health in the United States.
Every two years, the study participants were asked to complete questionnaires examining their health and lifestyles, which included detailed information about the foods they ate.
A total of 7,822 women diagnosed with type 2 diabetes aged 30 or older were included in the latest analysis, which appears in this week's issue of the journal Circulation.
Using the food questionnaires, the researchers were able to estimate the women's daily consumption of whole grains, bran, germ, and fiber.
Women who ate the most bran ate more than 10 times as much each day as women who ate the least (9.73 grams vs. 0.8 grams).
He says whole grains, especially fiber- and vitamin-rich bran, may protect the heart by reducing inflammation in the body.
Although the study included only women, Qi says the benefits of eating whole grains probably extend to men with diabetes. The Harvard researchers are conducting a similar study in men in hopes of confirming this.
Not All 'Whole Grain' Foods Equal
These days, many of the most highly processed breakfast cereals and other grain-based foods claim to be good sources of whole grain and fiber, but it isn't necessarily true, New York University nutritionist Marion Nestle, PhD, tells WebMD.
Popcorn, brown rice, whole-wheat flour, and long-cooking oatmeal are good, minimally processed whole-grain foods.
Determining how much whole grain is in heavily processed products is not so easy, Nestle says.
The American Heart Association recommends looking for the words "whole" or "whole grain" before the grain name in the ingredient list. The whole grain should also be the first product listed.
Nestle recommends looking for products that contain at least 5 grams of fiber per serving and that contain only ingredients that are easily recognized.
"If you don't know what a lot of the ingredients are, leave it on the shelf," she says.
The packaging for Kellogg's Froot Loops and Apple Jacks boasts that the breakfast cereals "now provide fiber." But the fiber content of the cereals is just 3 grams per serving.
General Mill's Banana Nut Cheerios and Lucky Charms boxes now say "whole grain guaranteed," but the cereals each contain just 1 gram of fiber per serving.
Kellogg's Frosted Mini-Wheats contain 5 grams of fiber per serving.
While she recommends reading labels, Nestle says focusing on a single food or food component misses the point that a healthy diet should include a wide variety of fruits, vegetables, and whole grains.