Colleagues and I just published a paper in the American Journalof Clinical Nutrition demonstrating beneficial effects of both soliddark chocolate and liquid cocoa on blood pressure, and blood flow,in overweight adults. This adds to an impressive body of worksuggesting potential health benefits of dark chocolate. But evendata dipped in chocolate requires some interpretation. A short-termbenefit of dark chocolate on various measures of cardiovascular riskis now well-established. The ingestion of dark chocolate, generallydefined as a product with a cacao (often, but incorrectly, referredto as cocoa) content of 60% or more tends to reduce the stickinessof platelets, an aspirin-like effect. Studies suggest anti-inflammatory effects, antioxidant effects, reductions in bothcholesterol and insulin levels, and as in our study, reductions inblood pressure and enhanced blood flow as well.
The novelties in our study include the testing of both solid darkchocolate and liquid cocoa in the same subjects, as well as thecomparison of standard and sugar-free cocoa. As compared to cocoa-free placebos, each of the preparations containing cocoa reducedblood pressure significantly 2 hours after ingestion, by roughly 3points. In a paper soon to be published, we report that similarbenefits were seen from drinking cocoa daily for 6 weeks, withoutweight gain resulting.
The primary outcome in our study is called endothelial function.The endothelium is the inner lining of blood vessels, and the cellsthere release chemicals that tell blood vessels when to constrictand when to dilate. We use an ultrasound machine to measure thechange in diameter of a blood vessel in the arm, called the brachialartery (if you can find a pulse in the front of your elbow, that'sit), because its behavior is a reliable predictor of the behavior ofthe coronary blood vessels that supply the heart.
We observed significant enhancement of endothelial function withroughly 2.5 ounces of dark chocolate, or a single cup of cocoa.Again, similar benefits were seen with daily cocoa ingestion. Theenhancement of endothelial function, and the reduction in bloodpressure, were greater with sugar-free cocoa than with regular,suggesting that sugar may compete with some of the beneficialeffects of cocoa.
Such benefits of dark chocolate make good sense. Cocoa isactually the most concentrated source of antioxidant nutrients,called flavonoids, commonly available to us. Heart health benefitsfrom dark chocolate may also relate to its high content of magnesiumand fiber.
The most interesting thing about dark chocolate is that it isclearly heart healthy despite being rich in saturated fat. But notall saturated fat is created equal. The particular variety ofsaturated fat that predominates in dark chocolate, called stearicacid, does not raise cholesterol or harm blood vessels. This is incontrast to the varieties of saturated fat that predominate in dairyand most meats, palmitic and myristic acid, which do. Milk chocolateis both lower in antioxidant content, and higher in potentiallyharmful fat content, than dark chocolate, and does not offercardiovascular benefit.
As a personal fan of dark chocolate, I suspect another benefit aswell. If you compare a dark chocolate bar to a milk chocolate bar,you will find the former has fewer ingredients, meaning there isless to compete with the native taste of chocolate. That, combinedwith the slight bitterness when cocoa content is high, means ittakes less to feel satisfied. Whereas sweet tends to put theappetite center into overdrive, a bit of bitterness tends to helpshut it down. I love dark chocolate, but there is only so much I caneat. And since too much of even a good thing is not a good thing,the fact that dark chocolate seems to help regulate its own dose is,well, a good thing.
Along with the CDC, which supports my lab, our study wassponsored by Hershey, which of course makes and sells chocolate.Corporate sponsorship always, and rightly, raises concerns aboutbias in research; studies have shown that company-sponsored studiestend to favor the interests of the sponsor. Certainly our resultsare everything Hershey could have hoped for. But we carefully buildinto our study methods protection against bias, such as analyzingthe data before we break the code to see which subjects were gettingactive treatment and which, placebo. Defense against bias may neverbe perfect, but ours is pretty darn good.
While we know with ever greater confidence that cocoa offersheart health benefits, we don't yet know for sure how to apply thatinformation. Should people eat or drink cocoa daily, every otherday, or weekly? If so, how much? If chocolate is added to the diet,is there a risk of weight gain that might offset other benefits?More research, perhaps some of it our own, will answer thesequestions eventually.
For now, here's my advice. If milk chocolate is part of yourdiet, switch out for dark chocolate. Your taste buds will adjust,and likely come to prefer the dark side if you give that chocolate achance. Make this switch, and you'll turn a food you love into afood that loves you back.
As for adding chocolate to your diet, the case to me seems verymuch like that for red wine, which also has known cardiac benefits:some is good, more is not necessarily better. If you can make roomin your diet for 1 to 3 oz of dark chocolate, or a cup of cocoadaily without gaining weight, it will likely be good for your heart.For what it's worth, my wife and I often find a bit of darkchocolate can help brighten our darker moods into the bargain.
Dr. David L. Katz can be reached at www.davidkatzmd.com.
