February 2012 Issue

Mining the Riches of Dark Chocolate
By Densie Webb, PhD, RD
Today’s Dietitian
Vol. 14 No. 2 P. 24

Research continues to show the phytochemicals in this decadent treat may lower heart disease and stroke risk.

Forrest Gump once recalled, “My momma always said, ‘Life is like a box of chocolates. You never know what you’re gonna get.’”

This memorable quote from the 1994 hit movie starring Tom Hanks holds much truth, and for many on Valentine’s Day, it’s not knowing what’s in the box of chocolates that makes the occasion—as well as life—so much more special.

On February 14, bite-size chocolates filled with nuts, nougat, caramel, toffee, coconut, or a cherry will be bestowed on lovers, spouses, and romantic hopefuls as symbols of love and affection. It’s fitting then that Valentine chocolates come in heart-shaped boxes, the universal symbol of love.

But there’s an unintended irony to the heart-shaped containers that was only recently discovered by researchers: Chocolate, minus its high-fat, sugary, creamy contents, may actually be good for heart health.

The first study suggesting that chocolate may not be the unhealthful, decadent indulgence it was long known as was published in 1994 in The American Journal of Clinical Nutrition. The researchers reported that substituting a milk chocolate bar for a high-carbohydrate snack didn’t affect levels of LDL cholesterol in the blood. Elevated levels of LDL are, of course, a risk factor for coronary heart disease (CHD).

Score one for chocolate!

Since then, well over 100 research and review papers have been published on chocolate, many showing a positive association between regular chocolate consumption and heart health.

“There’s an accumulating body of evidence from both short-term randomized trials and long-term observational studies showing that components of dark chocolate protect against cardiovascular risk factors and cardiovascular events,” says Elizabeth Mostofsky, MPH, a research fellow in the department of epidemiology at the Harvard School of Public Health and coauthor of a chocolate study.

The Good-for-Your-Heart Ingredient
That first chocolate study published in 1994 focused on the saturated fatty acid stearic acid found in chocolate, suggesting that its lack of cholesterol-raising effect explained the results. Since then, researchers have turned their attention to naturally occurring phytochemicals, known as flavanols, as being the heart-healthy ingredients in chocolate. Research suggests that these antioxidant compounds, mostly epicatechin, but also catechin and procyanidins, which are richest in dark chocolate, may increase vascular dilation and improve blood flow, reducing the risk of cardiovascular disease.1-4 According to the USDA Nutrient Database, cocoa powder is one of the richest sources of flavanols in the diet.

It’s believed that the flavanols in chocolate work by increasing the levels and the action of nitric oxide, a naturally occurring compound in the body that acts as a vasodilator, increases insulin sensitivity, and slows down the atherosclerotic process.5 Levels of flavanols have been reported to range from a low of 12 mg/oz of milk chocolate to a high of 709 mg/oz of baking chocolate, which is made of 100% cocoa solids.2

Where Does Chocolate Come From?
All chocolate comes from cacao (or cocoa) beans, which aren’t really beans at all but seeds of the fruit of the Theobroma cacao tree.3 Once harvested, cacao seeds and their surrounding fruit pulp are fermented by naturally occurring microbes. The seeds are then dried and shipped to processors, who remove the thin outer layer. The stripped-down seeds are roasted and milled to produce chocolate liquor. This liquor is used to make cocoa powder for both dark and milk chocolate.3

The process of drying, roasting, and fermenting the cacao beans reduces the bitter flavanol levels in the beans to provide the rich chocolate flavor most everyone knows and loves. Further processing to produce what’s known as Dutch chocolate reduces flavanol levels anywhere from 60% to 90%,6 although Dutch chocolate cocoa powder is still one of the top flavanol-containing foods.

Now that the health benefits of flavonoids are well known, chocolate makers face the unenviable challenge of striking a balance between flavor and healthfulness.1

Chocolate Research
Several systematic reviews and meta-analyses have found chocolate consumption to be associated with a lower incidence of hypertension and stroke.7 Epidemiologic studies have shown a link between chocolate consumption and a reduced risk of all cardiovascular disease, including myocardial infarction and heart failure.8-11 And clinical trials have suggested that cocoa, the main ingredient in chocolate, may help lower LDL cholesterol and inhibit its oxidation while raising HDL cholesterol levels.12 Chocolate also may have the ability to reduce platelet aggregation and have an anti-inflammatory effect.3

If the associations found in population studies are valid and the findings of clinical trials are reproducible, chocolate consumption could contribute to a reduced risk of cardiovascular disease.

A systematic review of three relevant studies on chocolate consumption and stroke was presented at the American Academy of Neurology meeting in 2010. Two of the studies found an association between weekly chocolate consumption and a lower risk of stroke (22%) and death from stroke (46%). A third study found no association between total flavonoid intake (including flavanols) and stroke or death when 3% of the flavonoids came from chocolate.7

Another analysis of 15 randomized controlled trials, in which flavanol dosages ranged from 30 mg to 1,000 mg/day and lasted for two to 18 weeks, suggested that dark chocolate has a small but clinically significant blood pressure-reducing effect on systolic hypertension or diastolic prehypertension but has no effect on normal blood pressure.4 The blood pressure-reducing effect in this analysis was similar to that found with other lifestyle changes, such as moderate physical activity.4 Clinical trials have found dark chocolate consumption reduces insulin resistance and has a similar blood pressure-lowering effect as the DASH (Dietary Approaches to Stop Hypertension) diet.13

A summary of 13 clinical trials, published in Hypertension in 2010, suggested that only through quality research can recommendations be made for reducing cardiovascular risk and unanswered questions be addressed, such as ideal dosing and timing, the effect of different brands of dark chocolate, and the feasibility of having people eat a prescribed amount of dark chocolate each day.5 However, Karin Ried, PhD, a research fellow at the University of Adelaide in Australia and a chocolate researcher, says, “Dosage doesn’t seem to play a key role. Regular consumption of low amounts of cocoa or chocolate can be beneficial for heart health.”

Another question that remains to be answered is whether chocolate has different effects in men vs. women.8 To date, no research has attempted to answer this question.

More recently, a meta-analysis of chocolate’s health effects was conducted on seven randomized controlled trials and observational studies that identified cardiometabolic disorders, including cardiovascular disease (CHD and stroke), diabetes, and metabolic syndrome.8 When the highest levels of chocolate consumption were compared with the lowest, a significant beneficial association was found for any cardiovascular disease (37% reduction), diabetes (31% decrease, based on one publication), and stroke (29% decline).

While no significant association was found in relation to heart failure in this meta-analysis, a recent prospective study of almost 32,000 women found that a modest intake of any kind of chocolate (one to two servings per week) was associated with a 26% lower incidence of heart failure compared with those who ate no chocolate.9

A cross-sectional study of almost 5,000 men and women who participated in the National Heart, Lung, and Blood Institute Family Heart Study found that, compared with those who didn’t eat chocolate, those who ate it at least five times per week had a 57% lower risk of CHD.10

Results from other research, however, haven’t all been positive. A randomized controlled crossover trial in Australia of 36 prehypertensive men and women who ate 50 g of dark chocolate per day found no blood pressure-lowering effect in dark chocolate.14 Another well-controlled study, published in the American Journal of Clinical Nutrition in 2008, showed no reduction in blood pressure or insulin resistance among 20 men and women with essential hypertension who consumed 150 mL of a flavanol-rich cocoa drink twice per day (900 mg flavanols/day).15

Not All Chocolate Is Created Equal
One of the biggest challenges in comparing the research on chocolate and health is the wide variety of the types of chocolate consumed in the studies. According to Oscar Franco, MD, PhD, of the University of Cambridge and a chocolate researcher, “The type of chocolate seems contradictory. Experimental evidence favors dark chocolate, but observational studies do not.” 

While clinical trials most often use dark chocolate, which can vary greatly in flavanol content, epidemiologic studies have examined overall chocolate consumption, including dark and milk chocolate. In addition, conducting double-blind studies with chocolate is difficult because flavanol-rich cocoa and chocolate products have a distinctly bitter taste.16

Milk chocolate, which is the most widely consumed chocolate in the United States, is much lower in flavanols than dark chocolate. But even dark chocolate can vary greatly in flavonoid content, depending on the amount of cocoa solids it contains and how it’s processed. Flavanol content even varies among crops of cacao beans. Manufacturers typically purchase cacao beans from several countries and from many suppliers and then combine them. This practice results in varying flavonoid levels from batch to batch of chocolate produced.13

The labeling of the flavanol content of chocolate products isn’t mandatory, but as a general rule, the higher the percentage of cocoa solids in a chocolate product and the more bitter the taste, the higher the flavanol levels. But while this association isn’t consistent,2 it‘s the best indicator available of flavanol content. And then, of course, there’s white chocolate, which isn’t chocolate at all, but cocoa butter; it contains zero flavanols.

Eat ’Til Your Heart’s Content?
So what should you advise clients and patients about chocolate? First, remind them that most chocolate products are high in sugar, fat, and calories. While much of the fat is the kind that doesn’t raise cholesterol levels, it does add a significant number of calories. It’s not wise to suggest clients add a daily dose of chocolate if it’s not already part of their diet, especially if they’re overweight or obese. However, some researchers have suggested that if total calorie intake is balanced, chocolate flavanols can be part of a healthful diet for patients with essential hypertension.

For chocolate lovers who regularly indulge, advise them to choose dark chocolates that are high in cocoa solids and therefore rich in heart-healthy flavanols. Increasingly, dark chocolate products are providing the percentage of cocoa solids on the label (as much as 70%), and some newer varieties, such as CocoaVia, are listing the amount of flavanols on the label, boasting as much as 350 mg per serving.

Despite these touted health benefits, Americans overwhelmingly prefer the taste of milk chocolate over dark—and we’re not alone. A study from Australia found that one-half of the participants in a 24-week period said it was hard to eat 50 g (about 23/4 oz) of dark chocolate every day, and 20% said it was an unacceptable long-term treatment option.14 Yet the truth is the darker the chocolate, the more bitter the taste and the more healthful it is for the heart.

The bottom line? Clearly, not everyone is a fan of dark chocolate, but it’s the one to recommend for heart health. Eating too much chocolate, like any high-calorie snack, can have harmful effects, but the research strongly suggests a potential health benefit from regular consumption of dark, flavanol-rich chocolate as part of a healthful diet. But the refrain from researchers is the same: We need more research before RDs can make any therapeutic recommendations.

— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.

 

References
1. Hurst WJ, Krake SH, Bergmeier SC, Payne MJ, Miller KB, Stuart DA. Impact of fermentation, drying, roasting and Dutch processing on flavan-3-ol stereochemistry in cacao beans and cocoa ingredients. Chem Cent J. 2011;5:53.

2. Langer S, Marshall L, Day A, Morgan M. Flavanols and methylxanthines in commercially available dark chocolate: a study of the correlation with nonfat cocoa solids. J Agric Food Chem. 2011;59(15):8435-8441.

3. Crozier SJ, Preston AG, Hurst JW, et al. Cacao seeds are a “super fruit”: a comparative analysis of various fruit powders and products. Chem Cent J. 2011;5:5.

4. Ried K, Sullivan T, Fakler P, Frank OR, Stocks NP. Does chocolate reduce blood pressure? A meta-analysis. BMC Medicine. 2010;8:39.

5. Grassi D, Necozione S, Lippi C, et al. Cocoa reduces blood pressure and insulin resistance and improves endothelium-dependent vasodilation in hypertensives. Hypertension. 2005;46(2):398-405.

6. Miller KB, Hurst WJ, Payne MJ, et al. Impact of alkalization on the antioxidant and flavanol content of commercial cocoa powders. J Agric Food Chem. 2008;56(18):8527-8533.

7. Sahib S. Chocolate consumption and risk of stroke. Abstract presented at: the annual meeting of the American Academy of Neurology; April 10-17, 2010; New Orleans, LA.

8. Buitrago-Lopez A, Sanderson J, Johnson L, et al. Chocolate consumption and cardiometabolic disorders: systematic review and meta-analysis. BMJ. 2011;343:d4488.

9. Mostofsky E, Levitan EB, Wolk A, Mittleman MA. Chocolate intake and incidence of heart failure: a population-based, prospective study of middle-aged and elderly women. Circulation: Heart Failure. 2010;3(5):612-616.

10. Djousse L, Hopkins PN, North KE, Pankow JS, Arnett DK, Ellison RC. Chocolate consumption is inversely associated with prevalent coronary heart disease. The National Heart, Lung, and Blood Institute Family Heart Study. Clin Nutr. 2011;30(2):182-187.

11. Buijsse B, Weikert C, Drogan D, Bergmann M, Boeing H. Chocolate consumption in relation to blood pressure and risk of cardiovascular disease in German adults. Euro Heart J. 2010;31(13):1616-1623.

12. Baba S, Natsume M, Yasuda A, et al. Plasma LDL and HDL cholesterol and oxidized LDL concentrations are altered in normo- and hypercholesterolemic humans after intake of different levels of cocoa powder. J Nutr. 2007;137(6):1436-1441.

13. Egan BM, Laken MA, Donovan JL, Woolson RF. Does dark chocolate have a role in the prevention and management of hypertension? Commentary on the evidence. Hypertension. 2010;55(6):1289-1295.

14. Ried K, Frank OR, Stocks NP. Dark chocolate or tomato extract for prehypertension: a randomised controlled trial. BMC Complement Altern Med. 2009;9:22.

15. Muniyappa R, Hall G, Kolodziej T, Karne RJ, Crandon SK, Quon MJ. Cocoa consumption for 2 wk enhances insulin-mediated vasodilation without improving blood pressure or insulin resistance in essential hypertension. Am J Clin Nutr. 2008;88(6):1685-1696.

16. Taubert D, Roesen R, Lehmann C, Jung N. Effect of low habitual cocoa intake on blood pressure and bioactive nitric oxide: a randomized trial. JAMA. 2007;298(1):49-60.

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