Besides adding calories, these can dilute the benefits of cacao. So snack smart: Stick to healthy chocolate with at least 70 percent cacao (or cocoa, which is cacao in its roasted, ground form). As long as the content is that high, says Mary Engler, Ph.D., a professor of physiological nursing at the University of California at San Francisco, you can reap the benefits from eating only small amounts. Because of its high fat and sugar content, limit yourself to 7 ounces, or about four dark chocolate bars, a week.