
Consuming dark, but not milk, chocolate may be associated with lower risk of developing type 2 diabetes, according to a new study from Harvard T.H. Chan School of Public Health.
There is an existing body of research on the relationship between chocolate and type 2 diabetes but findings have been inconsistent, and few studies have differentiated between types of chocolate (e.g., dark versus milk).
The researchers sought to fill this gap using data from the Nurses' Health Studies I and II and the Health Professionals Follow-up Study.
About the study
Over the course of 30+ years, 192,000 adult participants who were free of diabetes at the study's outset reported on their food habits every four years, including chocolate consumption, as well as their diabetes status and body weight.
By the end of the study period, nearly 19,000 of the participants reported being diagnosed with type 2 diabetes. Of the nearly 112,000 who reported specifically on their dark and milk chocolate intake, nearly 5,000 were diagnosed with type 2 diabetes.
The study found that participants who consumed at least five ounces of any type of chocolate per week had a 10% lower risk of type 2 diabetes compared to those who never or rarely consumed chocolate.
Dark chocolate had an even bigger impact: Participants who consumed at least five one-ounce servings of this chocolate per week showed a 21% lower risk of type 2 diabetes.
Consumption of milk chocolate, meanwhile, was not associated with reduced type 2 diabetes risk.
Increased consumption of milk chocolate, but not dark chocolate, was associated with long-term weight gain, a potential contributor to the development of type 2 diabetes.
How dark chocolate may protect
Dark chocolate is an excellent source of flavanols, phytochemicals in cocoa beans that have antioxidant and anti-inflammatory effects which may protect insulin-producing cells in the pancreas.
Flavanols also have blood-vessel-relaxing effects. One small clinical study showed that flavanols lowered blood pressure and improved insulin sensitivity in people with prediabetes.
Compared to other types of chocolate, dark chocolate has the highest cocoa content (50 to 90 per cent) and, as such, contains the most flavanols.
Milk chocolate has a lower cocoa content (about 35 per cent) and one-fifth of the flavanols of dark chocolate. White chocolate, which isn’t made from cocoa beans, has no flavanols.
The higher sugar content of milk chocolate may also contribute to why it doesn’t deliver the same metabolic health benefits as dark chocolate. One ounce of milk chocolate delivers 15 g of sugar (nearly four teaspoons worth), while an ounce of 70 per cent dark chocolate has 9 g (two teaspoons worth).
The higher the percent cocoa solids, the lower the sugar content. An ounce of 85 per cent dark chocolate, for example, contains 4 g of sugar.
"Even though dark and milk chocolate have similar levels of calories and saturated fat, it appears that the protective polyphenols in dark chocolate might offset the effects of saturated fat and sugar on weight gain and diabetes”, said the researchers.
Study limitations
The main limitation is the study’s observational design. It found a correlation between chocolate intake and diabetes risk which does not prove that eating chocolate results in a lower risk of developing diabetes.
The researchers stated that randomized controlled trials are needed to replicate the findings.
Participants' chocolate consumption was low relative to previously recorded national averages; the findings may not apply to individuals with very high chocolate consumption.
Source: BMJ, December 4, 2024.
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