High-cacao dark chocolate contains high levels of flavanol, a compound known for its heart health benefits. Harvard researchers followed 55,502 subjects for 13 years, comparing levels of high blood pressure, diabetes and cardiovascular disease to lifestyle traits. They found eating one serving per week of chocolate yielded a 17 percent lower risk and two to six servings a week 20 percent, and then leveled off after eating one or more servings per day.