In the never ending search for unhealthy foods that can be called healthy, we have dark chocolate. Dark chocolate contains a high proportion of cocoa, but also a nice proportion of fat. High in sugar, and thus calories, this more bitter version of the sweet stuff is unhealthy in more than a small dose.

This isn't stopping the news from touting it as a way to prevent stroke though. Oh no...research has shown that certain types of cocoa are beneficial so of course, that means dark chocolate must be too! (It helps that the chocolate maker Mars encourage the studies with a symposium after releasing a fortifed version of their chocolate bar in 2003).

What it all comes down to is, just like red wine and green tea, raw cocoa contains antioxidants, specifically flavanols, which increase blood flow in the blood vessels. The specific flavanol in cocoa (epicatechin) has been shown to decrease the infarct size if given preventatively to mice 90 min before  a stroke,  and to ease the damage for 3 hours after a stroke if given therapeutically (but the effect wears off by 6 hours).

Flavanol-enriched cocoa is drank by the Kuna Indians of Panama, a population  with very low cardiovascular disease rates. Brain research has shown increased blood flow to the cerebral vessels for 2-3 hours after consumption of the drink.

I've compiled some more research with links to the various studies here.

So yes, it is of interest. But nutritionally, it does not bode well for balanced diets. The effects on calorie intake and weight would be counter-productive.