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 recent observational study, which found that in fact, as dark chocolate consumption increased from none to five servings, so did the benefits.
The researchers emphasised that one serving is about 28.3g, and it must be dark chocolate to do the trick – milk chocolate lovers are out of luck. Sadly, report CNN, 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 TH Chan School of Public Health.
Cacao is the raw and less-processed form of chocolate harvested from the Theobroma cacao tree. It 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 like 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 – 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 Programme at Johns Hopkins Medicine in Baltimore, who was not involved in the study
“So it’s plausible the high flavonoid content in dark chocolate could have beneficial effects.”
A growing health concern
About one in 10 Americans have diabetes, and up to 95% of those have been diagnosed with type 2 diabetes, according to the US Centres 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 529m 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. Red wine contains flavanols as well, but again, I would not recommend wine either.”
Milk chocolate didn’t work
The study, published in The BMJ, analysed 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 more than 111 000 chocolate aficionados.
After adjusting for dietary and lifestyle risk factors, researchers found those who ate at least five servings a week of any type of chocolate showed a significant 10% lower rate of type 2 diabetes than 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, randomised 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 randomised control trial,” he added. “We need more randomised controlled clinical trials.”
There’s another concern as well, he said. 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 one small serving 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.”
Study details
Chocolate intake and risk of type 2 diabetes: prospective cohort studies
Binkai Liu, Geng Zong, Frank B Hu et al.
Published in The BMJ on 4 December 2024
Abstract
Objective
To prospectively investigate the associations between dark, milk, and total chocolate consumption and risk of type 2 diabetes (T2D) in three US cohorts.
Design
Prospective cohort studies.
Setting
Nurses’ Health Study (NHS; 1986-2018), Nurses’ Health Study II (NHSII; 1991-2021), and Health Professionals Follow-Up Study (HPFS; 1986-2020).
Participants
At study baseline for total chocolate analyses (1986 for NHS and HPFS; 1991 for NHSII), 192 208 participants without T2D, cardiovascular disease, or cancer were included. 111 654 participants were included in the analysis for risk of T2D by intake of chocolate subtypes, assessed from 2006 in NHS and HPFS and from 2007 in NHSII.
Main outcome measure
Self-reported incident T2D, with patients identified by follow-up questionnaires and confirmed through a validated supplementary questionnaire. Cox proportional hazards regression was used to estimate hazard ratios and 95% confidence intervals (CIs) for T2D according to chocolate consumption.
Results
In the primary analyses for total chocolate, 18 862 people with incident T2D were identified during 4 829 175 person years of follow-up. After adjusting for personal, lifestyle, and dietary risk factors, participants consuming ≥5 servings/week of any chocolate showed a significant 10% (95% CI 2% to 17%; P trend=0.07) lower rate of T2D compared with those who never or rarely consumed chocolate. In analyses by chocolate subtypes, 4771 people with incident T2D were identified. Participants who consumed ≥5 servings/week of dark chocolate showed a significant 21% (5% to 34%; P trend=0.006) lower risk of T2D. No significant associations were found for milk chocolate intake. Spline regression showed a linear dose-response association between dark chocolate intake and risk of T2D (P for linearity=0.003), with a significant risk reduction of 3% (1% to 5%) observed for each serving/week of dark chocolate consumption. Intake of milk, but not dark, chocolate was positively associated with weight gain.
Conclusions
Increased consumption of dark, but not milk, chocolate was associated with lower risk of T2D. Increased consumption of milk, but not dark, chocolate was associated with long term weight gain. Further randomised controlled trials are needed to replicate these findings and further explore the mechanisms.
Cocoa Extract Supplementation and Risk of Type 2 Diabetes: The Cocoa Supplement and Multivitamin Outcomes Study (COSMOS) (Open access)
The BMJ article – Chocolate intake and risk of type 2 diabetes: prospective cohort studies (Open access)
CNN article – Study looks at impact of two kinds of chocolate on type 2 diabetes risk (Open access)
See more from MedicalBrief archives:
Some dark chocolates may have health benefits
Why dark chocolate is good for the heart
US scientists flag lead and cadmium found in dark chocolate
Cognitive performance and cocoa flavanols – research review