A new Harvard study showed that people who eat dark chocolate daily may significantly lower their risk of developing type 2 diabetes by 21 percent, while milk chocolate does not appear to offer the same benefit.
The [study](https://www.bmj.com/content/387/bmj-2023-078386), published in the medical journal “The BMJ” on Dec. 5, marks a notable contribution to research involving flavonoid consumption and its effect on reducing type 2 diabetes risk.
Flavonoids are a group of nutrients present in various fruits and vegetables, including onions, kale, broccoli, green tea, and apples. They are also present in high concentrations in cacao beans—the basic ingredient of chocolate.
Prior studies into the positive effect of chocolate on diabetes risk were controversial due to their inconsistent results.
However, Binkai Liu, a doctoral student at Harvard’s Department of Nutrition and lead author of the study, found that previous research paid little attention to the differences in chocolate consumed.
Milk chocolate typically contains less than 50 percent cacao content, whereas dark chocolate contains between 50 to 90 percent cacao, depending on the brand and type.
Cacao beans in a file photo. (Kim Kyung-Hoon/Reuters)
Using data from three prior long-running studies, Liu and his team were able to detect a significant trend. After adjusting for personal, lifestyle, and dietary risk factors, those who consumed at least five ounces of any type of chocolate per week had a 10 percent lower risk of type 2 diabetes compared to those who never or rarely ate chocolate.
However, that ten percent was proved largely attributable to the consumption of dark chocolate. Participants who consumed at least five servings of dark chocolate per week showed a 21 percent lower risk of type 2 diabetes, whereas the association with lower diabetes risk was statistically insignificant for milk chocolate.
Instead, researchers observed significant weight gain associated with increased consumption of milk chocolate.
This shouldn’t surprise anyone; milk chocolate typically contains more butter (saturated fats) and sugar than dark chocolate—two known causes of weight gain associated with type 2 diabetes development.
In terms of diet, the research team found that those with a preference for milk chocolate tended to consume less healthy food overall, which may explain why milk chocolate had no effect compared to the relatively great effect of dark chocolate.
The team also observed a 3 percent reduction in type 2 diabetes risk for every serving of dark chocolate consumed per week.
The three studies—the Nurses’ Health Study, which ran from 1986 to 2018; the Nurses’ Health Study II, which ran from 1991 to 2021; and the Health Professionals Follow-Up Study, which ran from 1986 to 2020—followed more than 192,000 people over the course of 34 years.
All participants were screened and found free of diabetes, cardiovascular disease, and cancer at the start of their respective studies.
Of the 192,000 participants, 112,000 reported specifically about which type of chocolate and how much they ate. By the end of the studies, 4771 participants were found to have developed type 2 diabetes.
“Further randomized controlled trials are needed to replicate these findings and further explore the mechanisms,” the study concluded.