Last month the American Society for Nutrition (ASN) reaffirmed in a report that fiber-rich whole grains lower the risks of diabetes and heart disease. Media outlets such as Reuters duly reported the news, but many failed to point out a crucial detail: some whole grains may do nothing to reduce disease risks. In fact, many foods legally marketed as whole grains could actually harm health.
The term “whole grain” might evoke an image of a whole, intact grain—that is, a fiber-rich coating of bran surrounding a starchy endosperm and a small reproductive kernel known as the germ. But in a definition created in 1999 by the American Association of Cereal Chemists (AACC) International, an organization of food industry professionals and scientists, and adopted by the U.S. Food and Drug Administration in 2006, “whole grain” refers to any mixture of bran, endosperm and germ in the proportions one would expect to see in an intact grain—yet the grains can be, and usually are, processed so that the three parts are separated and ground before being incorporated into foods. (Refined grains, on the other hand, are grains that have been stripped of their bran and germ.) For a food product to be considered whole grain, the FDA says it must contain at least 51 percent of whole grains by weight. Compared with intact grains, though, processed whole grains often have lower fiber and nutrient levels.
In what it calls a scientific statement the ASN reviewed studies published about whole grains between 1965 and 2010. Descriptions in many studies did not conform to the current definition in that they considered foods such as wheat germ and bran cereals to be whole grain. (Both are now considered partsof a whole grain.) Ultimately, the researchers found that the only whole-grain-rich diets that reduced the risk of heart disease and type 2 diabetes were those that included bran as a whole grain or those that contained high amounts of fiber. Studies of “whole grains using the currently accepted definition don’t have enough data to support them for preventing these different chronic diseases,” says co-author David Klurfeld, the national program leader for human nutrition in the Agricultural Research Service at the U.S. Department of Agriculture.
One problem with the current definition of “whole grain” is that it doesn’t account for fiber—and many whole grain products on supermarket shelves contain very little. An individual would have to eat 10 bowls of Multi-grain Cheerios, 16 slices of whole-wheat bread, or nine cups of brown rice to get the fiber recommended for an American adult for one day. “There’s nothing wrong with eating brown rice, but you can't expect health benefits if you're going to be eating brown rice as your source of whole grains,” Klurfeld explains.
The common processing of whole grains—which can involve grinding, puffing and flaking them—can also impact their healthfulness. Processing can make whole grains tastier; it can give them a longer shelf life, too, by removing fats from the outer layer of the grain that can turn rancid. But some processing techniques have been shown to degrade natural antioxidants and reduce fiber content. In fact, the AACC International recently proposed modifying its definition of “whole grain” to allow for some nutrient losses during processing.