Chocolate Is Good for You, But . . .

Summarized by Robert W. Griffith, MD
May 25, 2005

Introduction

Lab studies have shown that cocoa and chocolate may protect the cells lining the blood vessels - the endothelium - by improving the availability of nitric oxide. This is due to antioxidant flavonols, which are a type of flavonoids found in dark chocolate, but not in white chocolate. Nitric oxide is important because it can increase insulin sensitivity, which is a desirable effect, especially in people who may be headed for the metabolic syndrome and other cardiovascular problems.

To check this out, Italian scientists did a study of the effects of dark and white chocolate on the blood pressure and insulin sensitivity in healthy people. Their findings are reported in the American Journal of Clinical Nutrition, and we summarize them here.

What was done

Fifteen volunteers (8 women, 7 men) were enrolled. Their average age was 34, and their average body mass index (BMI) was 22.6 (normal). They were not allowed to eat or drink any cocoa product for 7 days. Then they were randomly assigned to eat either 100 gram dark chocolate bars or 90 gram white chocolate bars, for 15 days.

After another 7-day 'wash-out' period during which they were not allowed any cocoa product, they crossed over to eating the other chocolate bars for another 15 days.

Blood pressure was measured every day. At the end of each 15-day chocolate-eating period fasting blood samples were taken, and then further sampling was done at 30-minute intervals after a 75-gram oral glucose drink. The blood glucose levels at these times were used to calculate the level of insulin sensitivity. Blood lipids were measured in the fasting samples.

What the analyses showed

The baseline examinations showed the volunteers were healthy, without any evidence of type 2 diabetes or high blood pressure. However, it was found that dark chocolate caused a significant effect on systolic blood pressure (the upper number). The average systolic level was 107 mmHg after 15 days of dark chocolate compared with 114 mmHg for white chocolate. Diastolic pressures (the lower numbers) were not significantly affected by the type of chocolate.

Insulin sensitivity was significantly greater after dark chocolate, compared with white chocolate, when tested by two different analysis methods.

What's the significance of these findings?

Research into possible benefits of cocoa followed the observation that Kuna Indians, who live on an island off Panama, have an extremely low rate of atherosclerosis, high blood pressure, diabetes, and abnormal blood lipids; and they consume a lot of cocoa-rich beverages. Cocoa, by improving the availability of nitric oxide, assists the relaxation of blood vessels and increases insulin sensitivity. The latter effect, which hasn't been shown before, is important in combating high blood pressure, obesity, and type 2 diabetes.

The good news is that you can (maybe should?) eat more chocolate, with two provisos: 1) it must be dark chocolate, and 2) you must watch the extra calories the chocolate brings with it!

Source

• Short-term administration of dark chocolate is followed by a significant increase in insulin sensitivity and a decrease in blood pressure in healthy persons. D. Grassi, C. Lippi, S. Necozione,  et al., Am J Clin Nutr, 2005, vol. 81, pp. 611--614

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