Eggs are cracking open some nutritional barriers.

After decades of being out of favor because of their high cholesterol content, this popular food is earning high marks as a low-cost source of protein. Eggs pack key vitamins and minerals, including iron. They're a good source of lutein, which may help protect vision. They're low in saturated fat, have zero trans fat and provide some healthy fat.

"Eggs certainly can be part of a healthy diet," said American Heart Association (AHA) president Robert Eckel, who cautions that even so, consumers need to track how much cholesterol they eat.

"Identifying the egg as the source of other nutrients is meritorious," Eckel said. "But dietary cholesterol is not necessary for health and we certainly don't want to add a potentially injurious substance at unlimited levels."

Dishes high in saturated and trans fatty acids, such as fried foods, are the major contributors of increased blood cholesterol levels. But studies have shown that eating an egg a day leads to about a 1 to 3 percent increase in blood cholesterol levels, according to a 2004 review published in the Journal of the American College of Nutrition by Stephen B. Kritchevsky, a researcher at Wake Forest University School of Medicine and a member of the Egg Nutrition Council's Scientific Advisory Board, an industry group. Large population studies show more mixed results for egg consumption. Some point to an increased risk of heart disease with varying amounts of eggs. Others show no additional risk or even a possible benefit, concludes Kritchevsky.

In people with diabetes, however, regular consumption of eggs appears to produce a significantly higher risk of heart disease. A 1999 study conducted at the Harvard School of Public Health and published in the Journal of the American Medical Association found that men with diabetes who ate one or more eggs per day had twice the heart disease risk of those who ate less than one egg per week. Women with diabetes who ate one egg per day had 1.5 times the risk of developing heart disease as those who ate one or fewer eggs per week.

More recent research suggests that foods high in dietary cholesterol play an independent role in increased risk of heart disease.

"That means," Eckel said, "that dietary cholesterol may increase the risk of heart disease by a mechanism that we do not yet understand."

That's why the current advice from government agencies and medical groups in the United States is to limit cholesterol to 300 milligrams daily, even for those whose blood cholesterol levels aren't high.

People who already have elevated blood cholesterol levels, heart disease or diabetes are advised to restrict cholesterol to 200 milligrams per day. Since a large egg contains 212 milligrams of cholesterol, "it makes it real difficult to incorporate more than one egg a day," said Penny Kris-Etherton, professor of nutrition at Pennsylvania State University.

Not all scientists agree that healthy people need to refrain from eating eggs and other foods high in cholesterol. In Australia and Canada, there is no upper limit on daily cholesterol intake for the healthy population. The National Heart Foundation -- Australia's equivalent of the American Heart Association -- is so convinced of the egg's nutritional benefits that it recently awarded eggs the "heart tick," a checkmark that guides consumers to nutritious foods.

"Using the Tick in this way advises the general population that eggs make a positive nutritional contribution to healthy eating," the group notes on its Web site.

"There will always be differing viewpoints," said Neil Stone, professor of medicine at Northwestern University in Chicago. "My worry is that the public will consider this a black-or-white issue when there is a certain amount of gray. But to tell people who have diabetes and heart disease that they can have as much dietary cholesterol as they want would be a mistake."

Here's what you need to know:

Skip the yolk whenever possible. An egg white has nearly four grams of protein but no fat and no cholesterol. In baking, substitute two whites for one whole egg. Cut cholesterol intake by using one yolk for every two to three whites when you make scrambled eggs, omelets and frittatas. Or take a tip from the AHA's Eckel: He eats omelets often, but makes them with egg whites only or with egg substitutes, which contain no cholesterol. Hate the idea of wasting yolks? Look for pourable egg whites, now available in many grocery stores.

Hedge your bets. If you add more eggs or other foods rich in cholesterol to your daily fare, get a blood cholesterol test now and another in two to three months to see if your levels have changed. Dietary recommendations are made for the general population. Individual response to eating high-cholesterol food can vary widely. "Some people are responders," says Alice Lichtenstein, professor of nutrition at Tufts University. "Some people are not. If you're not, then there's no reason to be concerned, but the only way you can tell is by getting a blood cholesterol test."

Track other sources of cholesterol in your diet. Egg yolks are a major source, but organ meats (liver, kidney, brains) are also very high in cholesterol. Delicacies such as pate are best eaten occasionally and only in small amounts. Crab, shrimp and squid are good sources of healthy omega-3 fatty acids, but they also pack cholesterol. A quarter-pound of shrimp has about the same amount of cholesterol as an egg yolk. So find a balance. Whenever possible, avoid fried fish, which adds saturated and sometimes trans fat.

Counterbalance cholesterol. A 2002 Institute of Medicine report noted that studies show diets low in saturated fat and containing healthy fats such as canola, corn or safflower oils can help blunt the effects of cholesterol-rich foods.

Look at the big picture. One meal, one day or even one week of high-cholesterol food will not likely affect your blood cholesterol levels. It's the overall pattern that counts. "Focus on your lifestyle," said Northwestern's Stone, "not on single food items. The two biggest things people can do diet-wise are, one, to limit saturated fat and trans fats and, number two, to avoid becoming overweight."

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