If you’ve long assumed that you must deprive yourself of delicious foods in order to be healthy, a new study published today in The BMJ offers encouraging news: Eating dark chocolate has been associated with a reduced risk of developing Type 2 diabetes.
The research did not prove that the chocolate itself was responsible for this health benefit; it could be something else about the people who ate dark chocolate that made them less likely to develop diabetes. And dark chocolate should not be considered a “magic bullet” for preventing diabetes, said Dr. Qi Sun, an associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health and the lead investigator on the study.
But the findings do build on a larger body of research demonstrating links between dark chocolate consumption and reduced risks of certain health conditions like high blood pressure, cardiovascular disease and insulin resistance.
The results, Dr. Sun added, suggest that a little dark chocolate can be part of a healthy diet.
What did the study find?
In the mid-1980s and early 1990s, researchers began studying three groups of predominantly white health professionals. Every four years, the more than 190,000 participants completed detailed diet questionnaires, which asked how often they consumed chocolate. Beginning in 2006 and 2007, depending on the group, the researchers tweaked the questionnaires to ask how often participants ate dark chocolate and milk chocolate. They followed the participants’ health for up to 34 years.
During that time, nearly 19,000 participants developed Type 2 diabetes. After adjusting for other aspects of their lifestyles, such as exercise, alcohol consumption, smoking and the overall healthfulness of their diets, as well as their age and family history of diabetes, the researchers found that people who consumed at least five servings of any type of chocolate per week had a 10 percent lower risk of developing Type 2 diabetes compared with those who rarely or never ate chocolate.
But when they drilled down into the data from the nearly 112,000 people who provided details on the types of chocolate they consumed, the researchers found an even more striking result: Those who consumed at least five servings of dark chocolate per week had a 21 percent lower risk of developing Type 2 diabetes than those who consumed dark chocolate less than once per month.
The participants who consumed milk chocolate, this subsequent analysis also revealed, were not protected from Type 2 diabetes. In fact, the researchers noted, they were more likely to gain weight during the study.
What were the study’s limitations?
While the study was large and well-designed, it could not prove cause and effect, said Dr. Susan Spratt, a professor of medicine in the division of endocrinology, metabolism and nutrition at the Duke University School of Medicine, who was not involved with the study.
Perhaps the people who consumed dark chocolate were healthier in other ways, she said. Maybe they exercised more, followed a healthier diet or could more easily visit a doctor when they needed to, for example.
The study group was also mostly white and well-educated, so the results may not apply to everyone, Dr. Sun and his coauthors noted.
The researchers accounted for many factors related to diet, lifestyle, education and wealth in their analysis, Dr. Sun said. But proving that eating dark chocolate prevented Type 2 diabetes would require a clinical trial on a large group of people, giving half dark chocolate and the other half milk chocolate, and following them for decades.
Such a trial would be expensive — and it would be unrealistic to devote that many years and resources to investigating a single food’s link to chronic disease, Dr. Spratt said. This is why nutrition scientists often use observational studies, such as this one, to examine the relationship between diet and health.
What might explain the result?
Dark and milk chocolate have similar amounts of calories, sugars and saturated fats, Dr. Sun said. But dark chocolate typically contains more cocoa, which may be key to its health benefits, he and his colleagues hypothesized.
Cocoa is a bean extract that is rich in fiber and beneficial plant-based compounds called flavonoids, said Dr. Dariush Mozaffarian, a cardiologist and the director of the Food is Medicine Institute at Tufts University, who was not involved with the study. Some research suggests that flavonoids have antioxidant and anti-inflammatory effects and might help to open blood vessels, which may explain cocoa’s health benefits, he said.
Some small, short-term clinical trials have suggested that consuming dark chocolate or cocoa can reduce blood pressure and improve insulin sensitivity and insulin resistance — both of which influence the risk of developing Type 2 diabetes, Dr. Mozaffarian said.
But not all of those studies have found benefits, and some used concentrated cocoa supplements, which contain more flavonoids than a typical bar of dark chocolate.
What is the takeaway?
Dr. Mozaffarian fully embraces dark chocolate as part of a healthy diet, though he says it is best to choose a variety with at least 70 percent cocoa. An even better option is nuts coated with dark chocolate, he said, since nuts also contain phytonutrients, healthy fats and fiber.
In several recent studies, researchers have found concerning levels of lead and cadmium in dark chocolate. More research is needed to understand this potential health risk, Dr. Sun said. However, those studies have suggested that consuming up to about an ounce of dark chocolate per day — an amount found in about a third of a regular-size Ghirardelli dark chocolate bar — is safe for most adults, though those who are pregnant may want to be more cautious.
If it turns out that dark chocolate does protect against Type 2 diabetes, it would not be at the top of Dr. Spratt’s list of ways to prevent the condition. To her patients, she emphasizes a diet rich in vegetables and whole grains; avoiding processed and red meats; maintaining a healthy weight; and getting at least 150 minutes of moderate-intensity physical activity per week.
In a study published in 2023, Dr. Mozaffarian and his colleagues estimated that about 70 percent of new cases of Type 2 diabetes worldwide — about 14 million cases per year — could be linked to poor diet.
Dr. Mozaffarian said that it is also helpful to limit added sugars and refined carbohydrates. But if you enjoy dark chocolate, it is OK to include it in your diet.
“People have this concept that healthy eating means eating things that don’t taste good,” he said. But many delicious foods are also healthy, he added.
“Dark chocolate is a great example of that,” he said.
