Whole Grains The Inside Story
The average American eats less than one serving of whole grains a day. Yet it would be hard to find an American who doesn't know that people need to eat more of them. But do Mr. and Ms. Average know why? Odds are, the reasons would surprise them.
Heart Disease
Why eat more whole grains?
“The strongest evidence is for cardiovascular disease ,” says Eric Rimm, an associate professor of epidemiology and nutrition at the Harvard University School of Public Health. For example:
• In the Iowa Women's Health Study of 34,000 women, those who reported eating at least one serving of whole grains a day had a 30 to 36 percent lower risk of heart disease than those who reported eating no whole grains.
• In the Nurses' Health Study of 75,000 women, those who said they ate roughly three servings of whole grains a day had a 25 percent lower risk of heart disease and a 36 percent lower risk of stroke than those who said they ate no whole grains.
• In the Health Professionals Follow-Up Study of 44,000 men, those who reported eating at least 42 grams of whole grains a day (about three servings) had an 18 percent lower risk of heart attack than those who reported eating less than 4 grams a day.
• Among more than 200 women with heart disease in the Estrogen Replacement and Atherosclerosis Trial, those who ate more than six servings of whole grains a week had less artery clogging over the next three years than those who ate whole grains less often.
Sounds like an open-and-shut case. But researchers aren't convinced that it was only whole grains that made the difference. “People who eat whole grains tend to do a lot of other healthy things, like exercising and not smoking,” explains Joanne Slavin, a professor of food science and nutrition at the University of Minnesota in St. Paul . They also get less saturated fat and more vitamins. “We try to account for those things, but they still might confound our results,” Slavin explains, because health-conscious people may do other things that scientists don't know about. To try to nail down cause-and-effect, researchers look for a mechanism that would explain how whole grains might protect the heart. Among the possibilities:
Cholesterol . Whole grains that are rich in water-soluble fiber -like oats and barley- lower LDL (“bad”) cholesterol . “There's no question that if you feed people soluble fiber in large enough doses, you can lower their cholesterol,” says Slavin. But most Americans-including all those nurses, health professionals, and Iowa women with a lower risk of heart disease-eat far less barley and oats than whole wheat, which is high in insoluble fiber. And wheat bran, one of the richest sources of insoluble fiber, doesn't lower cholesterol. Yet men who eat the most bran have the lowest risk of heart disease. “If you look at the fiber data, it's clear that grains rich in insoluble fiber are also protective,” says Slavin. “So you've got to look beyond cholesterol for an explanation.”
Insulin In a small study, researchers fed 11 overweight adults with high insulin levels 6 to 10 servings a day of either whole or refined grains. Fasting insulin levels were lower after six weeks on the whole grains than after six weeks on the refined grains. “Whole grains seem to improve insulin metabolism,” says David Jacobs, a professor of epidemiology at the University of Minnesota who co-authored the study. High insulin levels can raise the risk of both heart disease and diabetes. And a new study found a lower risk of the metabolic syndrome—which is linked to high insulin levels—in older people who eat whole grains. Nevertheless, says Slavin, “I wish we had bigger studies to prove that whole grains have an impact on insulin sensitivity.”
Antioxidants, etc. Whole grains are rich in antioxidants that may protect against tissue damage by scavenging marauding free radicals. But “the antioxidant story has big holes,” acknowledges Slavin. High doses of vitamin E, for example, don't prevent heart attacks. “It's possible that when you isolate antioxidants and take them in high doses, they don't work,” she says. Whole grains are also rich in a slew of other possibly protective substances, including plant sterols, lignans, phytates, vitamins, and minerals. “Magnesium is probably the number one mineral in whole grains that we need,” says Slavin. “Potassium is another. Both are needed but aren't typically added to fortified foods.” (See “White vs. Whole Wheat,”) Which, if any, of those constituents may make whole grains heart-friendly is still an open question. “We need more research to pin down the mechanisms,” says Slavin.
Diabetes
Do whole grains prevent diabetes?
In the Iowa Women's Health Study, the Nurses' Health Study, and the Health Professionals Follow-Up Study, people who consumed at least three servings a day of whole grains had a 20 to 30 percent lower risk of diabetes over the next decade or so than people who ate roughly one serving a week. But it's the heart disease story all over again. Researchers worry that something else about whole-grain eaters protects them. “We try to eliminate those confounders, but it's always possible that some are left over,” says Jacobs, “because people who eat whole grains have healthier behavior overall.” But he and others are encouraged by evidence for mechanisms that could explain why whole grains may prevent diabetes. Lower insulin levels is one possibility. Among the others:
Fiber. The soluble fiber in whole grains like oats and barley can keep carbohydrates from entering the bloodstream too quickly. “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 . 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 glycemic 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 U.S. ,” 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,” says 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 (see “The Whole Truth,” ). “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% 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 refifi 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 fl our. (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.
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