US researchers believe that by following a diet high in flavonoid-rich cocoa powder and dark chocolate consumers can witness a positive effect on their LDL ('bad' cholesterol) levels, as opposed to other diets that limit or exclude flavonoid sources such as tea, coffee, wine and onions.

The study was published in the November issue of the American Journal of Clinical Nutrition in the paper "Effects of cocoa powder and dark chocolate on LDL oxidative susceptibility and prostaglandin concentration in humans".

Scientists at Penn State University under Dr Penny Kris-Etherton, looked at ten men and 13 women aged between 21 and 62, who ate one of two experimental diets for four weeks. Half were allocated an average American diet altered to be low in flavonoids, while the remaining participants followed a diet containing about 22 grams of cocoa powder and 16 grams of dark chocolate.

They then ate their normal diet for a two-week break period, before switching to consume the experimental diet they hadn't already tried for another four-week period.

The scientists then evaluated and compared LDL (low density lipoprotein) susceptibility to oxidation while the participants were on each diet. The oxidation of LDL is believed to be an important part of the process of arteriosclerosis, the hardening of the arteries. Flavonoids, which are known to inhibit LDL oxidation, are therefore thought able to possibly delay the progression of the disease.

According to the paper: "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."

The study found that while eating the cocoa and chocolate containing diet, oxidation in the subjects' bodies occurred about 8% slower compared to when they ate the experimental average American diet.

Participants gave blood at the end of each diet period, and the researchers found that total antioxidant capacity was 4% greater after the cocoa and chocolate containing diet. HDL cholesterol (the 'good' cholesterol) was also 4% higher after the chocolate diet than after the average American diet.