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Why Is Dark Chocolate Good for You? Thank Your Microbes

Cocoa is good for your heart because of fermentation by gut bacteria, creating anti-inflammatory compounds that improve blood vessel function
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Credit: Jacek Nowak/Thinkstock

Dark chocolate might pack a double positive punch for our health—thanks to the microbes that live in our gut. New research suggests that beneficial bacteria that reside toward the end of our digestive tract ferment both the antioxidants and the fiber in cocoa.

In their deep-gut alchemy these microbes create anti-inflammatory compounds that have been linked to the cardiovascular and other benefits from dark chocolate consumption. The findings were presented March 18 at the American Chemical Society meeting in Dallas. Other new research helps explain how some of cocoa's widespread health benefits—from improving vascular function to increasing insulin sensitivity—may be linked—and good for even the young and the healthy.

Previous research suggested that cocoa components could be fermented to generate beneficial compounds. Daily consumption of dark chocolate or cocoa lowered people's blood pressure an average of two to three points (millimeters of mercury), according to a 2012 review (pdf) of 20 different studies. So John Finley, a professor of food sciences at Louisiana State University, and his students took the work a step further to see what else the body might be getting from this common treat—and how.

To follow cocoa through its digestive journey, they created a lab-built gut of sorts. (And for this, you may want to put down your chocolate momentarily.) "It's a rather disgusting process," Finley apologizes.

Down the artificial gut
The first step approximates the upper human digestive tract. The pure cocoa powder gets a wash of enzymes to mimic the early digestive juices. "So we are left with materials that are nondigestible," Finley explains. These nondigestibles get fed to the lower-intestinal gut microbes. But where to find them? From willing students, of course. About nine people proffered their poo to be harvested for an amalgam of microbes to stand in for an average gut community (granted one, Finley says, "on a typically unhealthy grad student diet."). The microbes then feasted on what was left of the cocoa after its passage through the mock digestive system. They fermented these compounds—flavonols that include catechin and epicatechin, which are also found in green tea—into smaller anti-inflammatories that could be absorbed into the bloodstream.

This bodily process seems plausible from both a biological and chemical standpoint, says Telmo Pereira of the Department of Cardiopneumology at the Superior College of Health Technology in Portugal. The next step, of course, will be more testing and looking for this transformation in humans, he notes.

As Grace Farhat, a researcher in the department of dietetics, nutrition and biological sciences at Queen Margaret University in Edinburgh, points out, we can't be entirely sure that each person's gut will undertake the same fermentation processes. "The composition of bacterial flora will vary in different individuals," she says. "This will mean certain individuals [likely] derive more benefits than others."

These new findings, however, could help explain why dark chocolate improves vascular function and cardiovascular health in general. Other recent research has found that regular moderate consumption of dark chocolate confers benefits even on the young and healthy.

Pereira and colleagues found that healthy young adults (of a mean age of about 20) who ate eight grams—about one small square—of 70 percent cocoa chocolate each day for a month had "an obvious improvement" in vascular function over their baseline as well as a control group. Those eating the extra chocolate saw their arterial flow (measured by flow-mediated dilation) increasing, on average, from 14 percent to 23 percent. The findings (pdf) were published earlier this year in Cardiovascular System and could have substantial implications for health on a broader population scale. "If consuming dark chocolate in moderate quantities has the ability to decrease the risk of heart disease, it could have a role to play in reducing medical costs" as well, Farhat says.

Cocoa has also been shown to improve insulin sensitivity, which Pereira points out could be a related mechanism—both getting a boost from the polyphenols, the antioxidants in cocoa. Research published earlier this year in Endocrine Abstracts showed that polyphenols in chocolate improved insulin sensitivity even in people who did not have diabetes. Adults consumed 20 grams of either polyphenol-rich or polyphenol-poor dark chocolate. Those with the extra polyphenol boost showed better insulin sensitivity after just a month. "The results imply that dark chocolate might delay or prevent the onset of diabetes and prediabetes," says Farhat, who led the work.

Of course, "chocolate is not a substitute for prescribed medications," Pereira notes. He suggests cocoa might work best for people who fall in the middle of the bell curve for cardiovascular health—something of a Goldilocks effect. "If you have a patient with severely compromised vascular function, you cannot expect benefits from chocolate," he says. And likewise, those who are already exceedingly healthy might not see much of a boost from extra cocoa. But both he and Finley suggest cocoa as a tool for helping in the effort to prevent some heart diseases. "Dark chocolate could well be a preventive nutritional supplement to consider," Pereira says. Or a preventative snack.

Biggest cocoa boost
Not all chocolate is created equal, however. Dark chocolate gets all the good publicity because it has relatively lower added sugar and fats than milk chocolate. "The benefits come from cocoa," Pereira notes—thus, "chocolates with the highest proportion of cocoa are better." Even when it comes to pure cocoa powder—which can be used for a hot beverage or added as a topping—no one knows the ideal amount. Even the darkest of the dark chocolates “must be consumed in moderation to avoid weight gain," he notes.

Finley and his team went straight for the pure, unsweetened cocoa powder to test its impact on gut microbes. Nevertheless, each type produced slightly different results. The researchers sent three types of cocoa powder down the lab-rigged digestive path: lightly processed, moderately processed and Dutch-processed. The more mildly treated the cocoa powder the more it produced beneficial compounds in these experiments. Farhat also noted that likewise some brands of dark chocolate "are low in polyphenols due to the methods of manufacturing."

With the high levels of polyphenols, cocoa might also be good for the gut itself; "It appears that if you were consuming some cocoas, it would actually stimulate the production of healthier microbes in the colon," Finley says. Additionally, the microbes broke down the undigested fiber in the cocoa, creating usable short-chained fatty acids, such as butyric, propionic and acetic acids. "The bottom line is that now I put cocoa powder on my oatmeal," Finley says.

Although his wife dismisses the nontraditional topping as a bit weird, Finley has science on his side for his breakfast combo: "The anti-inflammatory compounds combined with dietary fiber is a synergistic effect—one and one makes three" in this case, he says. And combining cocoa with additional sources of dietary fiber might boost the effect even more, as Finley suggests: "Maybe chocolate-covered black beans?"

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