How We Were Led to Believe Dark Chocolate is Healthy
Every once in a while, you'll meet one—the rare person who just doesn't care for the taste of chocolate. The rest of us not only enjoy it, we lust after it more than any other food. Many psychological studies, in fact, use chocolate as the holy grail of cravings, the ingredient that makes our mouths water at the mere thought of an impending treat.
So when studies come out that link chocolate to better health, we're primed to believe them. Take the finding, in 2015, that a chocolate bar a day aided weight loss. The news went everywhere, from The Irish Examiner to a TV news station in Texas. Too bad the whole thing turned out to be an elaborate set-up to make a point about sloppy media coverage of scientific research for a documentary debunking the diet industry.
And when a paper in the journal Heart last month linked chocolate intake to a reduced risk of atrial fibrillation—a potentially deadly fluttering heartbeat—headlines declared dessert good for the heart all over again. This was despite the fact that the study authors themselves wrote, right in the abstract, that "residual confounding cannot be ruled out."
An editorial accompanying the study practically predicted the positive coverage—"It is exciting to think about the potential for fun public health announcements, such as 'Eat more chocolate and prevent atrial fibrillation!' or 'A chocolate bar a day keeps the ablationist away!'" Duke researchers Sean Pokorney and Jonathan Piccini wrote.
But such slogans would be entirely premature, they went on to write. For one thing, chocolate consumers in the study were healthier, better educated, and exercised more than those who somehow went months without a bite of the sweet stuff—meaning you can't prove it was the candy that made the difference in their heartbeats.
Such issues pervade studies about nutrition in general, and chocolate in particular, making it difficult for the average person to draw useful information from them. Observational studies like this one involve taking a big group of people, asking them to check off what they ate (using food frequency questionnaires, which the study authors themselves point out raise concerns about "poor recall"), and then looking for associations between what people said they ate and the types of health problems they do—or don't—develop later on.
"Chocolate shows up as a factor but other foods might too. That's why you can't say chocolate is a cause of reduced atrial fibrillation; that observation could be due to any number of other factors," says the aptly named (but no relation to the chocolatiers) Marion Nestle, professor of nutrition, food studies, and public health at New York University.
She also mentions the recall issue: "I find these things [food frequency questionnaires] impossible to fill out because I can't remember at that level of specificity." Similar large, observational studies have linked cocoa or chocolate to a reduced risk of heart failure, diabetes, stroke, and cognitive decline. When studies uncover associations between certain foods and health benefits, scientists often work backward to understand why.
In the case of chocolate, they suspect compounds called flavanols—found in cocoa as well as tea, berries, and red wine—deserve much of the credit. Flavanols appear to increase the body's production of nitric oxide, a compound that dilates veins and arteries so blood flows more efficiently through the body. That includes to the brain, which may explain chocolate's potential effects on mood and cognition.
Flavanols may also keep red blood cells from becoming dangerously sticky and seem to increase insulin sensitivity, improving your ability to use the hormone to convert sugar into energy and ward off diabetes, says Georgie Fear, a registered dietician and author of Lean Habits For Lifelong Weight Loss.
A 2016 meta-analysis of randomized controlled trials—the gold standard for measuring the effectiveness of a given intervention, be it a new drug or a Hershey bar—found evidence that about 200 to 600 milligrams of flavanols a day improved insulin sensitivity and cholesterol levels. And a paper published earlier this year in the Cochrane Database of Systematic Reviews, well respected for its careful summaries of medical research, found an average dose of 670 milligrams reduced blood pressure by about four points in people with hypertension.
In both cases, the research reviewers point out that long-terms trials are needed to determine whether chocolate or flavanol consumption over time actually has a measurable impact on preventing things like heart attacks and diabetes—in other words, whether it truly can improve health and extend life. That's important to measure because, even if flavanols do confer benefits, they often come packaged with extra calories, sugar, and fats, says Philadelphia-based dietitian Libby Mills, national spokesperson for the Academy of Nutrition and Dietetics. So it's important to consider the whole picture when making dietary decisions.
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