In a study by Swiss and German researchers, lucky participants ate about 1.5 ounces of dark chocolate daily for two weeks. Ultimately, these chocolate nibblers had lower stress-hormone levels and a more regulated metabolism than a control group. Scientists speculate that chemicals in cocoa, such as flavonoids, play a role in regulating metabolism by alleviating stress that can cause your fat-burning engines to go on the fritz. Should you think this is a license to go wild, take heed: We’re talking small amounts of high-quality dark chocolate. Researchers say 1.5 ounces is enough.