Eating dark chocolate, but not milk chocolate, may be associated with a lower risk of type 2 diabetes, according to a study by the Harvard THChan School of Public Health, published online in The BMJ.

The researchers used data from three long-term US observational studies of female nurses and male health professionals. A total of 192,000 participants who had no history of diabetes, heart disease or cancer at the start of the studies and who reported their eating habits, including chocolate consumption, body weight and diabetes status, over 30 and over years old.

How much chocolate is good for us?

It found that study participants who consumed at least five servings of any type of chocolate per week (a serving equals about 28 grams) had a 10% lower risk of developing type 2 diabetes compared to those who rarely or never ate chocolate.

Dark chocolate had an even bigger impact. Those who consumed at least five servings of this chocolate per week had a 21% lower risk of developing type 2 diabetes. The researchers also observed a 3% reduction in risk for each serving of dark chocolate consumed per week.

The not so good milk chocolate

On the contrary, consumption milk chocolate was not associated with a reduced risk of developing type 2 diabetes, but was associated with long-term weight gain, a potential contributor to the development of type 2 diabetes.

Associate Professor in the Departments of Nutrition and Epidemiology at Harvard, Ki Shan, one of the authors of the study, explains that “although dark chocolate and milk chocolate have similar levels of calories and saturated fat, it appears that the rich polyphenols in dark chocolate may counteract the effects of saturated fat and sugar on weight gain and diabetes. This is an interesting difference that deserves further investigation.”

The researchers note, however, that the average chocolate consumption of the study participants was relatively low, so the findings may not extend to people with very high levels of consumption.