Study looks at impact of two kinds of chocolate on type 2 diabetes risk

By Sandee LaMotte, CNN

(CNN) — Eating at least five tiny servings of dark chocolate each week may lower the risk of developing type 2 diabetes by 21%, according to a new observational study. In fact, as dark chocolate consumption increased from none to five servings, so did the benefits, the study found.

Before you start scarfing down an entire chocolate bar, however, be aware that a serving is 1 ounce, and it must be dark chocolate to do the trick — milk chocolate lovers are out of luck. The study found eating milk chocolate was linked to excessive weight gain over time, a key contributor to the development of type 2 diabetes.

“Dark and milk chocolate have similar levels of added sugar, fat and calories, but the most important difference is that dark chocolate contains more cacao,” said lead author Binkai Liu, a doctoral student in the nutrition department of Harvard T.H. Chan School of Public Health.

Cacao is the raw and less-processed form of chocolate harvested from the Theobroma cacao tree. Cacao contains the highest levels of flavanols, so the greater the percentage of cacao listed on the label of the dark chocolate bar, the more flavanols it will contain. Flavanols act as antioxidants and reduce inflammation that can trigger or worsen chronic conditions such as heart disease and diabetes.

While the study could not prove cause and effect, it’s possible that higher levels of flavanols in cacao might be a reason for the different impact of the two chocolates, Liu said.

“The bioactive compounds in cacao called flavanols have been shown in animal studies and small-scale human experimental studies to improve insulin sensitivity and reduce oxidative stress and inflammation, all of which are components in the pathophysiology of diabetes,” said Dr. Nestoras Mathioudakis, co-medical director of the Diabetes Prevention and Education Program at Johns Hopkins Medicine in Baltimore.

“So it’s plausible the high flavonoid content in dark chocolate could have beneficial effects,” said Mathioudakis, who was not involved in the new study.

A growing health concern

About 1 in 10 Americans have diabetes, and up to 95% of those have been diagnosed with type 2 diabetes, according to the US Centers for Disease Control and Prevention. Globally, the news is even worse — a July 2023 study estimated there could be at least 1.31 billion cases of diabetes by 2050, up from 529 million in 2021.

Drivers of this trend include lower levels of physical activity, alcohol and tobacco use, and poor diets, including an overdependence on ultraprocessed foods.

An observational study published in September found every 10% increase in ultraprocessed foods led to a 17% higher chance of developing type 2 diabetes.

Chocolate can easily fall into the ultraprocessed category — so would a doctor actually suggest that a person at risk for type 2 diabetes eat any chocolate, even if it’s dark?

“Chocolate products are candy and contain sugar, so I don’t encourage people to consume chocolate for better glucose control, and I’m not sure that I would on the basis of this study alone,” Mathioudakis said.

“I would suggest alternative sources, especially dark berries such as blueberries, blackberries and pomegranates, apples and tea,” he said. “Red wine contains flavanols as well, but again, I would not recommend wine either.”

Milk chocolate didn’t work

The study, published Wednesday in The BMJ journal, analyzed data from three long-term studies — the original Nurses’ Health Study, the Nurses’ Health Study II and the Health Professionals Follow-Up Study.

Study participants completed food questionnaires every four years over a 25-year period. Researchers then looked at dark chocolate, milk chocolate and total chocolate consumption among over 111,000 chocolate aficionados.

After adjusting for dietary and lifestyle risk factors, researchers found those who ate at least five 1-ounce servings a week of any type of chocolate showed a significant 10% lower rate of type 2 diabetes compared with those who rarely or never ate chocolate.

However, when the types of chocolate were factored in, the data showed no significant reduction in diabetes risk when consuming milk chocolate.

People who ate at least five servings a week of dark chocolate, however, showed a significant 21% lower risk of type 2 diabetes and did not experience the long-term weight gain seen with milk chocolate.

Opting for fruits and veggies may be best

The study has limitations, the authors point out. People in the study were older White adults, and chocolate consumption was relatively low. In addition, the results conflicted with a December 2023 study that found no benefit for diabetes in cocoa consumption.

“The authors themselves reference a large, randomized controlled trial that gave 21,000 people 500 milligrams of cocoa flavanols, and it lowered the risk of death, but it did not lower the risk of diabetes,” Mathioudakis said.

“They are not clear about why their study is not aligned with that randomized control trial,” he added. “We need more randomized controlled clinical trials.”

There’s another concern as well, according to Mathioudakis. Recent studies have found dark chocolate and similar cocoa products are contaminated with lead and cadmium, two neurotoxic metals that are linked to cancer, chronic disease, or reproductive and developmental issues, especially in children. Organic versions of dark chocolate had some of the highest levels, likely due to industrial pollution in developing countries where cacao trees are grown.

What’s the takeaway? If you’re not a chocolate fan, it’s probably best to opt for fruit and vegetable sources of flavonoids and leave the candy alone, Mathioudakis said. If you can’t live without a piece of chocolate, however, try to keep it to 1 ounce of dark chocolate a few times a week.

“For anyone who loves chocolate,” Liu said, “this is a reminder that making small choices, like choosing dark chocolate over milk chocolate, can make a positive difference to their health.”

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