In that dark chocolate is rich in flavonoids, a type of antioxidant, previous studies have suggested its potential value in preventing coronary heart disease.   Sunil Kochhar, from the Nestle Research Center (Switzerland), and colleagues have found that a small portion of dark chocolate can ward off stress. The team studied 30 men and women, each of whom were classified by anxiety level. The study subjects consumed 20 grams of dark chocolate in the mid-morning and again in the afternoon.   Noting that those subjects with high anxiety traits had a distinct metabolic profile, the researchers observed that after two weeks of consuming 40 grams of dark chocolate daily, levels of stress hormones and other stress-related biochemical markers were reduced.  Postulating that dark chocolate, which is rich in a variety of bioactive compounds, may partially correct stress-induced imbalances, the team concludes that:  “The study provides strong evidence that a daily consumption of 40 g of dark chocolate during a period of 2 weeks is sufficient to modify the metabolism of … healthy human subjects, as per variation of both host and gut microbial metabolism.”