It's an old story, very old, in fact. Forbidden fruits taste the best. The apple in Eden may have started it all, but there are many modern equivalents, ranging from juicy burgers and crispy fries to salty snacks and fine cigars. But science and experience can also move things from column A to column B.
Far from being a guilty pleasure, alcohol, for example, can actually promote health if the dose is right (low) and the drinker is responsible. The same is true for nuts. On the other side of the coin, many people who think of exercise as a painful duty actually can come to experience it as pleasurable.
What about chocolate? Does it deserve its bad rap, or is it the latest thing in health foods? As for many complex questions, the answer is both, since the consequences of eating chocolate depend largely on the type of chocolate and the amount you consume.
A TASTE OF HISTORY
It all begins with the cacao tree, which originated in Central America more than 4,000 years ago and has been cultivated by humans for more than 1,000 years. The Aztecs and the Mayans were fond of the tree, believing that the seeds were a divine gift from paradise. Both groups used the cacao in religion and commerce; as currency, 100 beans had the value of one slave.
Chocolate was among the earliest American exports. Cortez brought cacao beans to Spain in the early 16th century. The Spaniards added sugar and cinnamon to the bitter Indian drink, and the rest is history. The cacao tree is now grown in equatorial regions of Africa and Asia as well as in the Americas, which still produce some of the world's cacao beans.
BEANS TO BARS
Chocolate doesn't grow on trees, but cacao beans do. After harvesting, the beans are dried for several days and then roasted. Next, the beans are opened, the shells are discarded, and the nibs are ground and separated into cocoa butter and cocoa powder. The powder is low in fat and is used for baking or to make hot chocolate, while the cocoa butter is the heart of the chocolate we eat.
Cocoa butter is dark and rich, but it tends to be bitter. To increase its appeal, confectioners process it further. One popular method is called Dutch processing; it makes the color lighter, but it also removes many of the ingredients that appear beneficial. To make chocolate sweeter, manufacturers add sugar, which also adds calories. And to make milk chocolate, candy makers really do add milk solids, which include saturated fats.
According to U.S. Food and Drug Administration standards, American milk chocolate can contain as little as 10 percent cocoa, and the agency is debating a proposal to allow candy makers to substitute vegetable oil for cocoa butter. Bottom line: Processing may make chocolate look lighter and taste sweeter but it also removes healthy ingredients and adds harmful ones.
A BITE OF CHEMISTRY
The cacao bean is devilishly complex, containing more than 400 chemicals. Many of them can affect human biology and health.
--Fats. Cocoa butter is high in fat. It's what gives chocolate its tempting texture and "mouth feel" but it's also what gives chocolate its bad name. Although it's true that the fat packs in a lot of calories, it's not guilty of the charge that it boosts blood cholesterol levels.
About a third of the fat in cocoa butter is oleic acid, the very same monounsaturated fat that gives olive oil its good name. Another third is stearic acid; it is a saturated fat, but unlike the three other saturated fats in the human diet, stearic acid does not raise cholesterol levels because the body can metabolize it to oleic acid. And while chocolate also contains some palmitic acid, a saturated fat that does boost cholesterol, careful studies show that eating chocolate does not raise blood cholesterol levels.
--Flavonoids. The humble cacao bean contains a number of chemicals in the flavonoid family. Polyphenols protect chocolate from turning rancid, even without refrigeration. Even more important are the flavanols, a group of chemicals that are responsible for many of the protective actions of chocolate. Flavanols are present in many healthful foods -- but dark chocolate is the richest source.
--Amino acids. Chocolate is high in tryptophan, phenylalanine,and tyrosine. Like other amino acids, these nitrogen-rich compounds are the building blocks of all the body's proteins. But two of these amino acids have a unique property: they are precursors of adrenaline, a "stress hormone," and dopamine, a neurotransmitter that relays signals between nerve cells in the brain. Scientists postulate that dopamine induces feelings of pleasure; if so, the passionate craving of the true chocoholic may have a neurochemical basis. But these chemicals may also explain some of the adverse effects of chocolate, including its ability to trigger headaches in some migraine sufferers, its ability to raise blood pressure to dangerous levels in some patients taking monoamine oxidase inhibitors for depression, and its ability to instigate diarrhea, wheezing, and flushing in patients with carcinoid tumors, which are rare.
--Methylxanthine. Chocolate contains two members of this group of chemicals. One is obscure, the other notorious, but both theobromine and caffeine have similar effects on the body. They may explain why chocolate makes some hearts beat faster, and why it gives many people heartburn by relaxing the muscle between the stomach and the esophagus, thus allowing acid to reflux up from the stomach into the sensitive "food pipe."
The flavonoids have many properties that might improve health. To see if they really work, researchers have studied foods ranging from apples to onions, and from tea to wine. And it's no surprise that chocolate has attracted the interest of scientists from around the world, giving the research an international flavor. Most studies concentrate on aspects of cardiovascular health; here are some representative findings:
--Antioxidant activity. Antioxidants protect many of the body's tissues from damage by oxygen free radicals. Among other beneficial actions, flavonoids protect LDL cholesterol from oxidation, which puts the "bad" into "bad cholesterol." Here are two examples: Scientists from Italy and Scotland fed dark chocolate, milk chocolate, or dark chocolate and whole milk to healthy volunteers. Dark chocolate boosted the volunteers' blood antioxidant activity, but milk, either in the chocolate or a glass, prevented the effect. Similarly, researchers in Finland and Japan found that dark chocolate reduces LDL oxidation while actually increasing levels of HDL ("good") cholesterol, but white chocolate lacks both benefits.
--Endothelial function. The endothelium is the thin inner layer of arteries. It's responsible for producing nitric oxide, a tiny chemical that widens blood vessels and keeps their linings smooth. Can chocolate help? Doctors in Greece think it may. They fed 100 grams (about 3½ oz) of dark chocolate to 17 healthy volunteers and observed rapid improvement in endothelial function.
Swiss investigators found similar effects from dark chocolate but no benefit from white chocolate. German scientists reported that flavanol-rich cocoa can reverse the endothelial dysfunction produced by smoking, and European doctors reported that dark chocolate appears to improve coronary artery function in heart transplant patients. There's good news for nonsmoking, original-heart men, too, since Harvard researchers found that cocoa can blunt the endothelial dysfunction associated with aging.
--Blood pressure. Because good endothelial function widens blood vessels, it's logical that chocolate might help lower blood pressure. Studies from Italy, Argentina, Germany, and the U.S. show that dark chocolate can lower blood pressure in healthy adults and in patients with hypertension. A 2007 meta-analysis of five trials that included 173 subjects found that the effect is modest, however, lowering systolic pressure (the higher number recorded, when the heart is pumping blood) and diastolic blood pressure (the lower number, recorded while the heart is resting between beats) by just under 5 millimeters of mercury (mm Hg). The benefit wears off within a few days of stopping "treatment" with a daily "dose" of dark chocolate. And another reality check comes from a six-week 2008 study of 101 healthy adults that did not find any benefit for blood pressure.
--Insulin sensitivity. Chocolate is a food that diabetics love to hate, and the sugar and calories give them good reason to eschew it. But an Italian study in nondiabetics suggested that dark, but not white, chocolate can improve insulin sensitivity. However, a small 2008 investigation of flavanol-enriched cocoa in diabetics found no improvement in blood sugar control or blood pressure.
--Blood clotting. Most heart attacks and many strokes are caused by blood clots that form on cholesterol-laden plaques in critical arteries. These clots are triggered by platelets; the antiplatelet activity of aspirin explains its important role in patients with coronary artery disease. Researchers in Switzerland and the U.S. found that dark chocolate reduces platelet activation.
FROM LAB TO LIFE
International experiments show that dark chocolate has an impressive array of activities: it's an antioxidant that may improve your cholesterol; it improves endothelial function and may lower your blood pressure; it is a sweet that may lower your blood sugar; and its antiplatelet activities could reduce your chances of developing an artery-blocking clot.
Taken together, these properties could reduce the risk of heart attack and stroke. But all of these hopeful results are based on short-term experiments in a small number of volunteers. Do these bits and pieces of data apply to real life? Perhaps.
Two large Harvard studies reported opposite results, but neither focused in on dark chocolate itself. The Harvard Alumni Study, which was limited to men, found that sweets seem to strengthen survival; during a five-year observation period, men who ate candy once or twice a week enjoyed a 27 percent lower mortality rate than candy abstainers. But even if candy is dandy, the study did not distinguish chocolate from other confections, so it's not possible to ascribe benefit to any particular type of sweet. In contrast, the Nurses' Health Study of women found no link between chocolate consumption and coronary artery disease -- but since the study did not distinguish between dark chocolate and other varieties, it could have missed a significant benefit.
The most robust support for chocolate as an asset to health comes from a 2006 report from the widely respected Zutphen Elderly Study. Researchers evaluated 470 Dutch men between the ages of 65 and 84; all were free of diabetes, cardiovascular disease, and cancer when the study began in 1985. Each volunteer provided comprehensive dietary information, and each underwent a detailed evaluation of his blood pressure, cholesterol, body fat, and other cardiovascular risk factors.
Researchers tracked the men for 15 years. They found that the men who ate the most cocoa-containing products had lower blood pressures than those who ate the least; the average difference was 3.7 mm Hg in systolic pressure and 2.1 mm Hg in diastolic. Those differences may not seen substantial -- but even after taking other risk factors into account, the chocolate lovers also enjoyed a 47 percent lower mortality rate; most of the benefit was explained by a sharply decreased risk of cardiovascular disease. And the largest single source of cocoa was dark chocolate.
RAISING THE BAR
To the ancient Mayans, chocolate was the food of the gods. Many modern Americans agree but others fear death by chocolate, assuming that anything tasting so good must be bad for you. Is chocolate a divine food or a devilish temptation?
Research suggests that chocolate may indeed have a role in promoting vascular health, but the devil is in the details. The first consideration is the type of chocolate. Dark chocolate appears beneficial, but milk chocolate, white chocolate, and other varieties do not.
The second issue is calories. Most trials have used 100 grams of dark chocolate, the equivalent of eating about one-and-a-half chocolate bars of typical size. If you ate that much every day, you'd pack in more than 500 extra calories, enough to gain a pound a week. And if that's not bad enough, remember that chocolate can trigger migraines, heartburn, or kidney stones in susceptible people.
If you're a chocolate lover, choose dark chocolate; the first listed ingredient should be cocoa or chocolate liquor, not sugar. Limit yourself to a few ounces a day, and cut calories elsewhere to keep your weight in line. And don't rely on chocolate to make up for a bad diet or insufficient exercise. But if you make dark chocolate part of a healthy lifestyle, you can have the pleasure without the guilt.
Modern science has learned a lot about this ancient food. Even so, more chocolate research is needed. Any volunteers?