Not all chocolate is created equal, and the kind that’s cheapest and easiest to get—sweet, highly processed bars—is the least likely to be beneficial.
The best option is plain cacao, either beans or nibs. The concentration of flavonoids, which seem to be generally beneficial, decreases with fermentation and roasting, so the closer you get to raw cacao, the better off you are. Flavonoids, in addition to promoting cardiovascular health, are very bitter, so you can use bitterness as a quick-and-dirty test for healthy cacao beans. It doesn’t work so well on sweetened chocolate, though, unless you know that the varieties you’re comparing have identical amounts of sugar.
If you get your chocolate in bars, you’ll want the maximum cocoa content. According to Chocolate and Health, “From experience, a dark chocolate containing about 2% flavanols [a subcategory of flavonoids] is really on the edge of being too bitter. Currently 70% cocoa chocolates only contain about 0.7% of flavanols because of heavy processing. The same chocolate would still be tasty with the flavanols content at least double.” This means that darker chocolates are often best. You can also look for makers that specify low roasting temperatures.
Because flavonoids are heat sensitive, their concentration changes when you cook or bake chocolate. There are a few tricks to maximize flavonoid content when cooking besides just keeping the temperature low. Cacao flavonoids survive best when cooked with minimal water and plenty of fat in high-density foods. For example, if you make a chocolate cake with cocoa powder it will lose more flavonoids than the same cake made with baking chocolate, which contains more fat. A dense brownie is preferable to a light, fluffy one.
If you’re cooking with cocoa powder, check whether it has been alkalized or “dutched.” This process was developed to help it dissolve better in water instead of clumping, but it can reduce the flavonoid content by over seventy percent. Alkalization may also affect the bioavailability of the flavanols that remain.
Special thanks to Joshua K. Endow, plant biologist, for sanity-checking this chapter!