Dark chocolate has a significant amount of saturated fat and sugar. According to Clemson University, a single ounce of dark chocolate is 150 calories, with the majority of calories coming from fat and sugar. Excess fat and sugar consumption can add inches to your waistline and increase your risk factors for cardiovascular disease. Clemson notes, however, dark chocolate is much more healthful than white chocolate or milk chocolate. Although dark chocolate is a rich source of antioxidants, it is only recommended in moderation because it is such a calorie-dense food.