Correction Appended

Carbohydrates have been taking a beating lately, blamed for the growing obesity epidemic, a raised risk of heart disease and diabetes, among others. To be sure, the carbs that predominate in the American diet -- sugars and refined starches -- deserve much of this unsavory reputation.

Consumed to excess as they are now, refined starches act like sugars. Each is widely considered a major culprit in making people overweight, and being excessively overweight adversely affects blood lipids and blood sugar, fostering heart disease and diabetes.

But there is another far more wholesome kind of carbohydrate -- whole grains, which make up only 5 percent of Americans' carbohydrate consumption.

Whole grains contain health-enhancing bran (the outer layer) and germ (the internal embryo) naturally found in all grains. When grains are refined to make white flour and white rice, for example, the bran and germ and all their healthful nutrients, antioxidants and other disease-fighting plant chemicals are systematically removed.

In January, researchers summarized the numerous health advantages of substituting whole grains for most of the refined starches now dominating Western-style diets at a conference exploring the health benefits of traditional Mediterranean-style foods. Oldways Preservation & Exchange Trust of Boston and the Harvard School of Public Health sponsored the conference.

The surgeon general's goal is for all Americans to consume at least three servings a day of whole grains, but the nation's daily average is now only about half a serving. Only 13 percent of Americans include at least one serving of whole grains in their daily diets.

The Food and Drug Administration allows food manufacturers to claim health benefits for their products with at least 51 percent whole grains by weight and less than 3 grams of fat per serving. It states, ''Diets rich in whole-grain foods and other plant foods low in total fat, saturated fat and cholesterol may help reduce the risk of heart disease and certain cancers.''

Whole grains contain no cholesterol, are low in fat and high in dietary fiber and vitamins and are also a good source of minerals. Though whole grains are concentrated packets of starch, they contain about 10 percent to 15 percent protein. But it is the indigestible fiber and phytochemicals in whole grains that render them stars in disease prevention.

A Role in Weight Control

Refined grains are almost pure starch, long chains of molecules of glucose, the blood sugar. Like sugar, most foods made from refined grains are rapidly digested and absorbed into the bloodstream, causing an abrupt rise in blood glucose and prompting the pancreas to spew out insulin to move the excess glucose out of the blood and into cells for energy and storage.

The sudden influx of glucose can cause an overproduction of insulin that results in enough of a drop in blood glucose to cause hunger to return in an hour or two, prompting people to eat between meals -- often snacks of sugars and refined starches.

But when a food contains all or mostly whole grains, digestion and absorption are slowed by the fibrous bran and by the protein and fat in the germ, increasing satiety and delaying the return of hunger. People who eat more whole grains tend to weigh less than those who consume fewer.

For example, in a study of 3,627 men and women followed for seven years, those who ate the most whole grains -- more than nine times a week -- weighed five to eight pounds less, on average, than those who consumed the least (no more than twice a week) of these foodstuffs, Dr. Simin Liu of Brigham and Women's Hospital in Boston reported.

Highlighting the Benefits

People who eat whole grains are healthier and live longer. In a continuing study of nearly 34,000 Iowa women, initially aged 55 to 69, Dr. David Jacobs at the University of Minnesota School of Public Health and colleagues found that those who ate at least one serving of whole-grain foods a day, primarily as bread and breakfast cereal, had a significantly lower rate of death from all causes when compared with women who ate almost no whole grains.

Several large prospective studies have highlighted the contributions whole grains can make to health and longevity.

For example, among the Iowa women, whole grain intake is directly related to a decreased risk of coronary heart disease, the leading killer of women and men in the United States.

Likewise, a Finnish study of 21,930 male smokers and an American study of 43,757 male health professionals found a reduced risk of heart attacks among those who ate the most whole-grain bread and cereal.

Although soluble fiber in whole grains is known to lower artery-damaging cholesterol, other components of whole grains contribute to cardiovascular protection, including antioxidants, phytic acid, lectins, phenolic compounds, amylase inhibitors and saponins. Dr. Joanne L. Slavin, a professor of food and nutrition at the University of Minnesota, says the protection probably comes from a combination of compounds in whole grains.