What Is a Whole Grain?
"Theoretically, if the absorption of carbohydrates were slowed, you'd have less stress on the pancreas, and insulin levels wouldn't shoot up," says Alice Lichtenstein of the U.S. Department of Agriculture Jean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston, Mass.
But most whole grains (and wheat bran) are rich in insoluble fiber, which doesn't slow absorption. "The quantities of soluble fiber we consume would have only a small effect on insulin," Lichtenstein cautions.
- Glycemic index. Many people assume that whole grains raise blood sugar levels less than refined grains (in other words, that whole grains have a lower glycemie index). However, what matters isn't whether the grain is whole or refined, but whether it's finely ground (like flour) or intact (like bulgur or brown rice).
"Whole-grain flour has nearly the same glycemic index as refined flour," says Jacobs. "Intact whole grains have a low glycemic index."
The bottom line: "This is a very preliminary area of whole-grain research," says Slavin.
Bowel Function
"Whole grains may have their biggest impact in the bowel," where fiber helps keep things moving, says Slavin.
For example, Australian researchers gave 28 overweight, middle-aged men enough whole-grain wheat or rye (about eight ounces of bread, cereal and crackers) to bring their fiber to 32 grams a day. (That's about what experts now recommend, and about twice as much as the average American man consumes.) Stool weights were higher than when the men ate low-fiber versions of the same foods (only 19 grams of fiber a day).
"Insoluble fiber is beneficial for bowel function, which is a huge problem in the United States," says Lichtenstein.
Obesity
"When people eat whole grains, they feel full sooner, so they eat fewer calories," says Slavin. "But could eating more whole grains help people lose weight? It's never been tested."
Women and men who consume more whole grains gain less weight over a decade or so than those who consume more refined grains. But the difference is only a pound or two.
And, once again, it's not clear if whole grains cause less weight gain or if health-conscious people who eat whole grains also watch their weight.
"It's difficult to study obesity because so many things contribute to it," says Harvard's Eric Rimm. "But there's a growing body of evidence to suggest that whole grains are important, maybe just because they make people get full faster."
Colon Cancer
If there's one benefit people expect from whole grains, it's a lower risk of colon cancer. But the evidence is shaky.
Some studies found a lower risk of colon cancer in people who ate more fiber from whole grains, fruits and vegetables, but other studies didn't. Then two clinical trials on people who had had precancerous colon polyps came up empty.
Researchers found no fewer new polyps in those who were told to eat more wheat bran or more fiber-rich grains, fruits and vegetables for three or four years than in those who ate their usual diets.
"It is clear that the high-fiber diet did not keep polyps from recurring, but what that means about fiber and colon cancer is less clear," s\ays the University of Minnesota's David Jacobs.
The Bottom Line
Science aside, some experts are nervous that the food industry may oversell foods with just a smidgen of whole grains.
"We get too little exercise and eat too much high-calorie food," says the University of Minnesota's Joanne Slavin. "Our diet is broken, and you can't fix it by adding a few grams of whole grains or fiber."
What's more, it's risky to urge Americans to eat more food, especially snack foods, even if they are whole grain.
"When I see 100 percent Whole Grain Chips Ahoy, I get worried," says Tufts University's Alice Lichtenstein. "We want to encourage a shift to whole-grain products, but I don't want to give people the impression that they should eat more cookies.
"In a country where two out of three adults are overweight or obese, we eat too much of everything already," she adds. "Do most of us have the discretionary calories to fit a cheese Danish made with whole grains into our diets?"
Despite the uncertainties, most researchers are convinced that replacing refined grains with whole grains is wise.
"Without long-term, randomized clinical trials of whole grains and disease, I don't have proof that the benefits of whole grains are real," says Jacobs.
"But I am 100 percent in favor of encouraging people to eat whole grains. I go back to the theory that phytochemicals as bundled in plant foods are good until proven otherwise."
And, experts note, there's no evidence that refined grains lower the risk of disease or obesity.
"Encouraging people to buy bread where the first ingredient is whole wheat clearly will do no harm," says Rimm. "And there's pretty strong evidence that it will be beneficial for heart disease and diabetes."
White vs. Whole Wheat
What do you lose when whole wheat is refined? Plenty. The gold bars show how little of 13 key nutrients remains. For example, refined flour has just 7 percent of the vitamin E, 13 percent of the vitamin B-6, and 16 percent of the magnesium of whole wheat flour.
The red bars show the five nutrients that are added back to refined flour to make it "enriched." Whole wheat is clearly more nutritious than enriched flour, with one exception: Enriched flour not only has more folate, but the added folate (folic acid) is absorbed better than the folate that occurs naturally in whole-wheat flour. (The higher-than-whole-wheat levels of B-1, B-2, and iron in enriched flour aren't reason enough to pick enriched over whole wheat.)
Some experts recommend that women who could become pregnant eat a mix of enriched and whole grains to get enough folate to reduce the risk of neural tube birth defects. A smarter strategy: Take a multivitamin to make sure you get enough folate, and eat whole grains to get fiber plus a raft of vitamins, minerals, and who knows how many phytochemicals that may protect your health. That's not bad advice for everyone.
© 2006 Mayo Foundation for Medical Education and Research. Distributed by Tribune Media Services, Inc.
Nutritionist Susan Mitchell attempts to crack the whole-grain code.
Get to the heart of a healthy diet.
Keep your heart pumping strong with tips from the Heart Health Insider.
