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For years, all chocolate was cast off as junk food. But now, thanks to stacks of research, doctors and nutritionists know that dark chocolate can actually be very healthy – when eaten in moderation. "Dark chocolate, made from the cocoa bean, is rich in a class of plant nutrients called flavonoids," says Jennifer McDaniel, MS, RD, spokesperson for the Academy of Nutrition and Dietetics. "The main type of flavonoid with antioxidant qualities is flavonols, which have been shown to lower blood pressure, boost blood flow, and reduce blood clots."

Dark chocolate may even go as far as protecting against heart attack and stroke. A large Australian study from 2012 found that daily consumption of dark chocolate could prevent major cardiovascular events in people with risk factors for heart disease. Additionally, a German study published in 2010 tracked 20,000 people over eight years and found that those who ate one square of chocolate a day had 39 percent less chance of stroke and heart attack.

Beyond heart health, dark chocolate may also protect against diabetes. "Some studies have shown that the antioxidants in dark chocolate may help the body use its insulin more efficiently to control blood sugar," McDaniel says. It also has potential to make you smarter – at least in the short term. A British study found that the flavonols in chocolate boost blood flow to brain, which could aid alertness and cognition. Plus, dark chocolate has a modest amount of caffeine, along with the milder stimulant theobromine, making it a great all-natural pick-me-up.

Along with antioxidants, dark chocolate also contains healthy fats. Cocoa butter, the fatty part of cocoa beans, is the unsaturated type that's beneficial for your heart and cholesterol levels. But even the saturated fat in dark chocolate isn't so bad for you. "Dark chocolate contains stearic acid, a saturated fat that may have a neutral effect on blood cholesterol levels," McDaniel says.

But here's the catch with dark chocolate: To get all of these health benefits, you have to choose the right kind. "It is a myth that all dark chocolate is good for you," says McDaniel. "Sugar is often the first ingredient listed on many dark chocolate bars." Steer clear of these. Instead, you want a dark chocolate that has "cocoa solids" listed first. "Cocoa solids contain the desirable flavonols responsible for heart health protection, so they should hold the number-one spot on the ingredients list," McDaniel says. "A good rule of thumb is to look for at least 70 percent cocoa solids, which means the chocolate will have a slightly bitter taste. But you can train your taste buds over time to enjoy this less-sweet flavor." You also want to avoid dark chocolates that have added milk fat or hydrogenated vegetable oils – both of which are saturated fats.

Once you've found a dark chocolate that fits this bill, McDaniel says go for it. "One of the most common food cravings I see from my clients is chocolate," she says. "If you can contain your consumption of dark chocolate – aim for about 100 calories or less per day – you should feel good about the enjoying this antioxidant-rich, potentially heart-protective sweet."