For years, chocolate lovers have remained blissfully unaware of the precise reason bittersweet dark chocolate seems to improve cardiovascular health. At least until now, that is.
On Tuesday, researchers at a meeting of the American Chemical Society in Dallas said they had solved the confection conundrum: specific chocolate-loving microbes in the gut converted an otherwise indigestible portion of the sweet into anti-inflammatory compounds, they said.
Using a series of modified test tubes to simulate humans' gurgling guts, researchers exposed several forms of cocoa powder to digestive juices and enzymes, and then to bacteria found in samples of human faeces. What they found was that after cocoa was "digested", long molecules called polyphenolic polymers remained within the gastrointestinal, or GI, tract.
The molecules were too large to cross the gut walls and be used as nutrients, said researcher John Finley, a professor of food science and biochemistry at Louisiana State University.
"They do nothing for us except travel down the GI tract after we consume them," Finley said. That was until they encountered some of the many microbes that inhabited the human colon, particularly Bifidobacterium and lactic acid bacteria.
"These little guys say, 'Hey, there's something in there that I can use,' and they start to break it down," Finley said.
The smaller molecules that resulted from this fermentation can travel through the gut wall and be used by the body.
"These materials are anti-inflammatory and they serve to prevent or delay the onset of some forms of cardiovascular disease that are associated with inflammation," Finley said.
A number of short-term studies have suggested that dark chocolate can cause blood vessels to dilate, and thus lower blood pressure.
It has been unclear exactly why this happens, but researchers had focused on the effects of anti-oxidant flavanols, such as catechin and epicatechin.
Finley said that the amount of cocoa powder that appeared to produce beneficial effects was about two tablespoons a day.