Dr. Penny Kris-Etherton, Penn State distinguished professor of nutrition and leader of the study, says, "Cocoa and chocolate are 'fun foods' and I think these results show that they can contribute to a healthy diet - especially if they are used in forms that don't include large amounts of fat and sugar. However, cocoa and chocolate shouldn't be considered significant sources of flavonoids in the same category with fruits and vegetables which also have fiber, vitamins and minerals."
The current study was the first to evaluate and compare LDL (low density lipoprotein) susceptibility to oxidation when the test subjects, 23 men and women, ate an average American diet purposely made low in flavonoids and a diet that contained about one and a quarter oz (38 grams) of cocoa powder and dark chocolate which are rich flavonoid sources. Oxidation of LDLs is thought to play an important role in the development of atherosclerosis or hardening of the arteries. Increasing LDL's resistance to oxidation is thought to possibly delay the progression of the disease. Flavonoids, which are present in a wide variety of plants, have long been known to inhibit LDL oxidation.
The study is detailed in a paper, "Effects of cocoa powder and dark chocolate on LDL oxidative susceptibility and prostaglandin concentration in humans" published in the current (November) issue of the American Journal of Clinical Nutrition. Kris-Etherton's co-authors are Ying Wan, who earned her M.S. in nutrition at Penn State; Joe Vinson, a faculty member at the University of Scranton; Dr. Terry D. Etherton, distinguished professor and head of the dairy and animal science department; John Proch, a technician at the University of Scranton; and Sheryl A. Lazarus, scientist in the Analytical and Applied Science Group, Mars Inc. The study was supported by the American Cocoa Research Institute.
In the study, 10 men and 13 women, ages 21 to 62, ate one of two experimental diets, either an average American diet altered to be low in flavonoids or a diet containing about three quarters of an ounce (22 grams) of cocoa powder and a half ounce (16 grams of dark chocolate) for four weeks. After a two-week break in which the participants ate their habitual diet, they switched for another four weeks to the experimental diet they hadn't consumed during the first four-week period.
Both experimental diets contained the same amount of caffeine and theobromine, which are stimulants found in chocolate and cocoa. Cocoa butter was used in baked goods in the average American diet to match the amount of cocoa butter in the dark chocolate.
The cocoa and dark chocolate were incorporated into the experimental diet in milk or pudding snacks or baked into cookies or brownies and eaten throughout the day by the subjects.
The subjects had blood drawn at the end of each diet period. The LDL was extracted from each blood sample and then subjected to oxidation in the laboratory. The researchers noted the amount of time it took for oxidation to begin, the rate at which oxidation proceeded and the amount of oxidized fatty acid produced.
When the subjects ate the cocoa and chocolate containing diet, oxidation occurred about 8 percent slower compared to when they ate the experimental average American diet. Analysis of their blood plasma also showed that total antioxidant capacity was four percent greater after the cocoa and chocolate containing diet. HDL cholesterol (the "good" cholesterol) was four percent higher after the chocolate diet than after the average American diet.
The paper notes "The incorporation of dark chocolate and cocoa powder into the diet is one means of effectively increasing antioxidant intake. Furthermore, the inclusion of dark chocolate and cocoa powder in a diet that is rich in other food sources of antioxidants, such as fruit, vegetables, tea and wine, results in a high antioxidant intake and may consequently reduce the risk of cardiovascular disease." Kris-Etherton adds, "An important caveat is that chocolate be incorporated sensibly and prudently in a healthy diet that emphasizes the intakes of fruit, vegetables, whole grains, skim milk, reduced-fat dairy products, fatty fish and lean meats, fish and poultry. A balanced dietary approach that includes a wide variety of foods in the diet is preferred to total exclusion of certain foods. Nonetheless, we would be remiss in endorsing unlimited quantities of chocolate."