Dark chocolate is chocolate made with nothing but chocolate liquor, cocoa butter, and sugar. The term is used to distinguish it from milk chocolate, a vastly inferior substance made mostly of sugar and milk solids, with far less chocolate, and proportionately less flavor.
This node mostly concerns the recent, well-publicized claims that dark chocolate promotes good health. I've tried to gather information on every specific claim that is being made about it as well as providing some other information about the health effects of everyone's favorite sweet. The first section is a discussion of what dark chocolate is.
A bit of background
Chocolate is the product of the cacao plant, Theobroma cacao, a tropical evergreen that produces large pods filled with seeds. To make chocolate, the beans from the cacao plant are fermented and then dried, roasted, and pulverized into a fine, fatty mass. This mass is semi-liquid and is known as chocolate liquor; it can be cooled directly to yield baking chocolate. Chocolate liquor can be separated by pressing it to remove the fat, which is known as cocoa butter, and leaving the solids behind as cocoa.
Dark chocolate is made by combining chocolate liquor with cocoa butter (there are further processing steps involved at this point), sugar, and usually an emulsifier like lecithin and often vanilla or other flavorings. Milk chocolate, in comparison, contains milk solids and usually considerably more sugar. In many cases the product contains more milk and sugar than chocolate. The result is that dark chocolate contains as much as 70% cocoa (cocoa solids and butter), or even more in the case of some specialty chocolates. Milk chocolate, of course, contains far less. There is a great deal of variation in the quantity of cocoa found in chocolates; bittersweet chocolate contains more than sweet chocolate, and fine chocolate usually contains more than cheaper products. The ingredients list in a Hershey's milk chocolate bar, for example, are "Milk chocolate (sugar, milk, cocoa butter, chocolate), soya lecithin (an emulsifier), and vanillin (flavoring)." Chocolate doesn't even show up until the fourth spot on the list.
Dark chocolate is darker in color, more intense in chocolate taste, and has a greater proportion of the chemicals purported to offer health benefits. For a more thorough discussion of how chocolate is made, check out the the chocolate node.
The health benefits of dark chocolate
I decided to write this because there have been an enormous number of stories in the media suggesting that dark chocolate offers various vague health benefits. I've attempted to find exactly what research motivated these claims; I tend towards skepticism of any health information offered by the media, and obviously the chocolate story is pretty attention-grabbing, which motivates news sources to inflate weak or premature claims.
What's it do to your plumbing?
A study printed in the July 18, 2005 issue of the journal Hypertension divided twenty patients into two groups, feeding one half a 100 gram bar of dark chocolate and the other half white chocolate for 15 days, and then switched the two groups. The patients' systolic blood pressure decreased by 11.9 mmHg on average, while their diastolic decreased by 8.5 mmHg; small decreases in circulating LDL cholesterol occurred as well. The researchers suspected that naturally-occuring flavonoids, which are absent in white chocolate, were the cause. This echoed findings from a 2004 article in the Journal of the American College of Nutrition. This study gave 21 subjects a 46 gram bar of dark chocolate per day for two weeks or a similar chocolate bar with its flavonoids removed. Those consuming the flavonoid-rich dark chocolate did better on a test of arterial stiffness, a possible contributor to atherosclerosis, than the placebo group did. But neither of these findings demonstrates any real effect on health — only on proxy measures that are used to guess at health.
A lot of the chocolate hype started in 2001 with an article in the American Journal of Clinical Nutrition. That article suggested that modest reductions in LDL oxidation - which may contribute to heart disease - could be found in patients given a diet supplemented with cocoa powder and dark chocolate. In truth, though, the study itself admitted that the claims were modest at best, and potentially irrelevant. (Which didn't seem to effect the media coverage of the findings.) Furthermore, the study was small (only 23 subjects), and it was funded by the American Cocoa Research Institute! A 1999 editorial in the same journal discussed chocolate's high saturated fat content, and declared that chocolate is "pathogenic" - it probably contributes to heart disease rather than preventing it.
Chocolate and the brain
Another thing we've been hearing a lot about lately is that chocolate stimulates the release of endorphins and serotonin in the brain. Endorphins (from endogenous and morphine) are polypeptides that seem to make us feel better and fight pain; serotonin is involved in mood regulation and many antidepressant drugs work by creating higher levels of seritonin in the brain. Ergo, says the media, chocolate fights depression.
So let's think about this claim. Endorphins are released by the body in response to all sorts of things - pain, exercise, stress, laughter, hot peppers, pleasurable foods. Saying that chocolate causes endorphins to be released isn't really significant at all - people like it and so it makes them happy! Gosh, doing things you like makes you happy. Real shocker, ain't it? As for serotonin, it also seems like a pretty weak claim. A 1999 article in the Journal of the American Dietetic Association links carbohydrate cravings with low serotonin levels, and suggests that large amounts of carbohydrates may stimulate serotonin release - except that protein blocks that effect, and chocolate contains sufficient protein to prevent serotonin release. The serotonin effect, if it exists at all, is related to the sugar rather than anything else.
So what's in chocolate?
Saturated fat
Cocoa butter is primarily composed of stearic acid (35%), oleic acid (35%), and palmitic acid (25%). The first and last are saturated fat, while oleic acid is monounsaturated. A typical chocolate bar might contain around a third fat, making it about 20% saturated fat by weight. So the 100 gram quantities used in the studies that seem to deliver adequate amounts of the potentially active phytochemicals will deliver 20 grams of saturated fat - a whole day's worth.
If you're really up on your reading, you might have heard claims that stearic acid, despite being a saturated fat, doesn't seem to cause the health problems that other saturated fats do. Stearic acid doesn't raise serum cholesterol levels, and it's converted by the liver into the much more benign oleic acid, a heart-healthy fat. Thus, stearic acid is acceptable for your health, right? Well, that's probably not the case, unfortunately. The Nurses' Health Study, a major 14 year study of 80,000 nurses, looked at the impact of diet upon heart disease. And the findings were clear - stearic acid is every bit as likely to contribute to heart disease as other long-chain saturated fats. The implications of this in analyzing other claims are important. In many cases, studies that are hyped as suggesting some health benefit are actually showing an improvement in some proxy measure of health, which may or may not actually reflect a real impact on health. There are always confounding variables that make these extrapolations dangerous.
H3C O
\ //
N -- C Caffeine
/ \
N -- C N -- CH3
\\ /
|| C -- C
/ \\
C -- N O
\
CH3
Caffeine and theobromine
Caffeine and theobromine are closely related naturally-occuring stimulants. They belong to a group of chemicals called methylxanthines. A single methyl (CH3-) group is different between them. A hundred grams of dark chocolate might contain about 60 mg caffeine and 500 mg of theobromine (keep in mind that this is a very substantial serving of chocolate); for comparison, a cup of brewed coffee contains no theobromine but 100 mg or so of caffeine. Keep in mind that the caffeine and theobromine content of chocolate is highly variable from brand to brand and from batch to batch.
The caffeine content of chocolate in typical serving sizes is not enough to have any major psychological effect. Theobromine is not as well studied as caffeine; it seems to have similar but much less intense stimulatory effects, lasting over a longer period of time. Administration of theobromine in pills does not have any effect on chocolate cravings, suggesting that it's not responsible for the seemingly addictive qualities of chocolate, and some researchers believe it has little to no psychological effect at all. The possiblity exists that caffeine and theobromine together have a synergistic effect, but there is as yet no evidence to support this hypothesis. Thus, the stimulant effects of chocolate appear to be fairly weak overall.
HO
\ Epicatechin
C == C
/ \
C C -- O C == C
\\ // \ / \
C -- C C -- C C -- OH
/ \ / \\ //
HO C -- C C -- C
\ \
OH OH
Antioxidants
This is the good part. See, dark chocolate is chock full of flavonoids, a class of plant pigments, and a subset of the polyphenols, that appear to have a variety of benefits for health. And dark chocolate is actually more concentrated in flavonoids than any of the other foods commonly touted for their antioxidant content. Dark chocolate appears to be better than red wine or green tea when it comes to antioxidant content. Antioxidants are an important group of chemicals that include vitamins C and E and numerous substances produced within the body. They help neutralize free radicals produced by biological mechanisms within cells as a normal aspect of their operations. Free radicals tend to damage other molecules, and are thought to be involved in aging, the development of atherosclerosis, the decline in brain function occurring with age, and the development of cancer. Thus, antioxidants may be extremely useful chemicals in improving health.
The basic problem with all of these claims is that we don't know what antioxidants in food do to your health. With most of these chemicals, not enough research exists to prove that they do anything to you at all. We don't even know whether most of these things can pass from the gut into the bloodstream — this is not a simple matter as the body is extremely selective in which chemicals cross into the blood. From there, it remains to be established that they can somehow make their way into the tissues and thence to the cells in which they might presumably do their work. How long they persist in the body, what concentrations are required to work, and whether they can actually function in that environment are all largely unknown. Their effects at clearing up harmful chemicals are known from experiments in vitro, not from what they've been shown to do in living organisms.
Most of the hype regarding antioxidants has really been the result of speculation. One theory explaining the tendency of French people to live long lives despite diets full of saturated fat and a tendency to smoke a lot is the supposed health protective effect of red wine. Red wine is thought to be beneficial because it contains antioxidants. Therefore, other foods rich in the same antioxidants must be healthy as well. Right? It depends on a lot of unproven assumptions.
Among these chemicals are procyanidins, a complex group of molecules that appear to break down into epicatechin (pictured above) and several other chemicals in the body. One of the few studies looking at whether the procyanidins in chocolate actually reach the body was the 2001 article I mentioned earlier (on LDL oxidation) and showed that only small amounts of epicatechins actually reached the blood and that they didn't last long, though they appeared to have minor effects of LDL oxidation (which is involved in formation of artery-narrowing plaques in the development of cardiovascular disease). The trouble is that you can't safely extrapolate from a brief, minor drop in LDL oxidation to claiming that eating some chocolate every day helps ward off heart disease. Whether the impact measured — or even the relevance of the assay used — has been questioned. And it's certainly not safe to guess that the modest impact of consuming the antioxidants in chocolate compensates for the large amount of saturated fat in chocolate. Other research has indicated that very likely, only a few of the procyanidins present in food can actually be absorbed, as most of them tend to simply be too large to enter the bloodstream.
What is known is that milk wholly prevents the absorption of epicatechins. So we can say with certainty that the proposed mechanism for chocolate's supposed health benefits does not apply whatsoever to milk chocolate, nor does it apply to hot cocoa (which would otherwise be a good way to get the health benefits of chocolate, since cocoa is far lower in fat than chocolate.) It doesn't apply if you drink milk too soon before or after eating chocolate, either. Not enough is known about the absorption of these chemicals to guess whether other things in the diet might also prevent them from reaching the blood — assuming that once they're there, they do anything significant.
Research on the other antioxidants that chocolate contains has been similarly equivocal. What has been clearly proven is that chocolate has fairly high amounts of some antioxidants, as measured by how well they work in test tubes. What has not been shown is what they do in the human body, or what impact those chemicals have on health in the long term. Oh, and one further depressing note — the concentration of these chemicals varies an enormous amount from brand to brand and batch to batch. So you can't be sure the chocolate you're eating has these chemicals that might hypothetically benefit your health anyway.
Conclusion
The incredible noise we've heard about the benefits of chocolate is really educational in one respect: it demonstrates the unreliability of health reports in the newsmedia. Reporters covering these topics may not have the education to make much sense of them, and since they're pressed for time, it's very common that they only read the abstract — if even that much — of the studies they're reporting on. Nevertheless, the newspapers report over and over that dark chocolate is beneficial for the health. You need to eat it every day. It's awfully convenient that a food we all love (and if you don't, there's something deeply wrong with you) is magically full of all sorts of health benefits. Very convenient, if you wish to use exciting health reporting to sell newspapers.
Match that to the hype machines that form the advertising departments at major corporations. A recent ad for Hershey's Special Dark chocolate (which, incidentally, is edible, a step up from the candlewax taste of their regular chocolate, but certainly no great shakes) hints at health benefits for it. Studies financed by chocolate manufacturers are cited in newspaper articles, and then referenced in TV commercials. What's beyond debate is that eating plenty of chocolate is beneficial. The problem is that the benefits probably mostly accrue to the manufacturers.
References
Bruinsma, Kristen and Taren, Douglas L., 1999. "Chocolate: Food or Drug?" Journal of the American Dietetic Association.
Connor, William E., 1999. "Harbingers of coronary heart disease: dietary saturated fatty acids and cholesterol. Is chocolate benign because of its stearic acid content?" American Journal of Clinical Nutrition.
Engler, Mary B. et alia, 2004. "Flavonoid-Rich Dark Chocolate Improves Endothelial Function and Increases Plasma Epicatechin Concentrations in Healthy Adults". Journal of the American College of Nutrition.
Grassi, Davide et alia, 2005. "Cocoa Reduces Blood Pressure and Insulin Resistance and Improves Endothelium-Dependent Vasodilation in Hypertensives". Hypertension.
Nestel, Paul J., 2001. "How Good is Chocolate?" American Journal of Clinical Nutrition.
Wan, Ying et alia, 2001. "Effects of cocoa powder and dark chocolate on LDL oxidative susceptibility and prostaglandin concentrations in humans". American Journal of Clinical Nutrition.
The Nurses' Health Study (http://www.channing.harvard.edu/nhs/)
My apologies as I wrote this over time and I'm not sure I managed to dig up every article I used in the research.