According to a popular saying, there are four basic food groups: milk chocolate, dark chocolate, white chocolate and chocolate truffles.

Whether or not you subscribe to this sugarcoated view of nutrition, make no mistake: Chocolate can not only win hearts this Valentine's Day, but there's evidence to suggest that it may help mend them too.

Dark and sweet, chocolate was once reserved for the royal and the very rich. Today, chocolate is often comfort food for the masses. Americans consume an estimated 11 pounds of chocolate (more than 26,000 calories) per year, according to a study published in the American Journal of Clinical Nutrition.

Popular, of course, doesn't necessarily mean nutritious. "Chocolate is not a health food," said Jeffrey Blumberg, director of the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. "Broccoli, yes, you can eat all you want. Dark chocolate, I can't say that about."

Even so, Blumberg noted that his lab and others have found tantalizing evidence that the ingredients in dark chocolate can help promote healthier hearts, reduce the risk of some types of cancer, improve insulin sensitivity and control blood pressure.

"The whole thinking about chocolate has changed through the years," said Penny Kris-Etherton, professor of nutrition at Penn State. "At one point, we thought it had no adverse effects because it didn't raise blood cholesterol levels, but now we understand that it has beneficial effects."

The promise of such health benefits has prompted one major chocolate manufacturer to set up a small pharmaceutical company to explore turning chocolate's ingredients into a drug. The effects come from plant-based substances known as flavonoids that are also found in green tea and in red wine.

The darker the chocolate, the more flavonoids it generally contains, "although that's not a guarantee," Blumberg noted. Chocolate containing 70 percent or higher of cacao seems to pack the most flavonoids

Studies show that these flavonoids lower blood pressure in people with hypertension and can keep it low in healthy individuals. On the remote Ailigandi Island off the coast of Panama, the Kuna Indians eat a diet rich in fish and fruit. Unlike many indigenous people, their meals also contain enough sodium to rival the diets of their countrymen living in developed areas. But the Kuna sidestep an age-related rise in blood pressure that occurs worldwide.

How? Scientists ascribe it to their practice of sipping five or more cups daily of a cocoa beverage.

Until about 100 years ago, sipping was pretty much the only way chocolate was consumed, according to Beth Kimmerle, author of "Chocolate: The Sweet History." That practice changed around the turn of the 20th century when Pennsylvania candy maker Milton Hershey and European chocolatiers figured out how to mass produce chocolate bars.

The heart of the matter

Whether dark chocolate is consumed as a beverage or a bar, it can also help prevent platelets from clumping in blood, clumping that helps set the stage for heart attacks and strokes. Chocolate improves vascular reactivity -- the ability of blood vessels to dilate when stressed and a key factor in reducing risk of heart disease -- in both "healthy people and people with heart disease," Blumberg said.

Recent studies also point to a possible role for chocolate flavonoids in prevention of breast and prostate cancer and in improving blood flow to the brain -- a finding that hints at protection against Alzheimer's disease and other forms of age-related dementia.

Just don't look for those benefits from either white chocolate, Dutch cocoa or milk chocolate. All are either low in flavonoids or devoid of them.

And, of course, even dark chocolate has some downsides. In January, Australian researchers reported in the American Journal of Clinical Nutrition that women 70 to 85 who consumed chocolate daily had lower bone density -- linked to fractures -- and strength than their counterparts who ate less chocolate.

Plus, with about 150 calories per ounce, "chocolate is high in calories and fairly high in fat," noted Dennis A. Savaiano, professor of foods and nutrition at Purdue University. Much of that fat is healthy, but chocolate also packs a fair amount of unhealthful saturated fat.

"No one is suggesting that you go out and eat three servings daily of chocolate or even two," Savaiano said. "But if you're going to have some candy, it seems to me that dark chocolate is among the best choices and, in moderation, it can be part of a heart-healthy strategy."

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