Whole Grains: The Inside Story

Whole grains are on a roll.

In 2005, the government's dietary guidelines advised Americans to "make half your grains whole" or to "eat at least 3 ounces of whole-grain cereals, breads, crackers, rice or pasta every day."

Meanwhile, "whole grain" claims have been popping up on labels of foods that may (or may not) deliver the goods.

What can whole grains do for you? Researchers are cautious about making wild promises, but one thing is clear: There's some evidence that whole grains can lower your risk of heart disease, stroke, diabetes, obesity and constipation ... and no evidence that refined grains can.

The average American eats less thon 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 percent 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, Minn.

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."

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.

What is a whole grain? >