Chocaholic gut bacteria may be one of the chief reasons why dark chocolate is good for the heart, research suggests.
By breaking down indigestible chocolate compounds and fermenting cocoa fibre, they generate a potent anti-inflammatory effect.
It is this, scientists believe, that helps to protect the heart and arteries from damage.
Researcher Maria Moore, from Louisiana State University in the US, said: "We found that there are two kinds of microbes in the gut: the 'good' ones and the 'bad' ones.
"The good microbes, such as Bifidobacterium and lactic acid bacteria, feast on chocolate.
"When you eat dark chocolate, they grow and ferment it, producing compounds that are anti-inflammatory."
"Bad" gut bacteria, such as Clostridia and some strains of Escherichia coli (E.coli) help to trigger inflammation, leading to bloating, diarrhoea and constipation.
The team tested three types of cocoa powder, the raw ingredient used to make chocolate, in an artificial digestive tract consisting of a series of modified test tubes.
Cocoa contains antioxidant polyphenol compounds such as catechin and epicatechin and a small amount of dietary fibre.
Both components are poorly digested and absorbed, but are readily processed by the friendly bacteria in the colon.
"In our study we found that the fibre is fermented and the large polyphenolic polymers are metabolised to smaller molecules, which are more easily absorbed," said Dr John Finley, who led the Louisiana team.
"These smaller polymers exhibit anti-inflammatory activity. When these compounds are absorbed by the body, they lessen the inflammation of cardiovascular tissue, reducing the long-term risk of stroke."
The findings were presented at the American Chemical Society's annual meeting in Dallas, Texas.
Combining cocoa with prebiotics - indigestible food ingredients that stimulate bacterial growth - is likely to enhance the process with beneficial results, said Dr Finley.
"When you ingest prebiotics, the beneficial gut microbial population increases and out-competes any undesirable microbes in the gut, like those that cause stomach problems," he added.
Prebiotics are found in foods such as raw garlic, raw wheat bran, and cooked whole wheat flour, and are especially abundant in raw chicory root. They can also be obtained from widely available supplements.
Combining dark chocolate with fruits such as pomegranates or acai may also boost its benefits, said Dr Finley.