Nutritional Pearls: Does Eating Chocolate Prevent Diabetes?

Thomas is a 43-year-old man of healthy weight and body mass index. Despite his health, he expresses concern about diabetes, as the disease is common in his family.

He tells you that recently he has seen numerous reports online about the benefits to diabetes risk enjoyed by people who regularly eat chocolate. While Thomas has never loved chocolate, he is willing to try to eat more of it if you think it will help.

How do you advise your patient?

What is the correct answer?
(Answer and discussion on next page)

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Timothy S. Harlan, MD, is a board-certified internist and professional chef who translates the Mediterranean diet for the American kitchen. He is an associate clinical professor of medicine and executive director of The Goldring Center for Culinary Medicine at Tulane University in New Orleans. Dr Harlan is the 2014 co-chair and keynote speaker at the Cardiometabolic Risk Summit in Las Vegas, October 10-12. 

Answer: Research on how chocolate benefits diabetes risk adds to our knowledge that cocoa is good for you, but it is not conclusive.

As I've noted in the past, medicine is not like algebra, where if A = B and B = C, then A = C. So if a food contains an ingredient, and that ingredient has been linked with a certain positive or negative effect, it does not necessarily follow that the food will also have that effect. (Boy, it would be great if it did!) In medicine, it's critical to connect those dots with specific research.

Chocolate is a case in point. Cocoa, from which chocolate is made, is high in flavonoids and contains both caffeine and magnesium. All 3 of those ingredients have been separately linked to a reduced risk of diabetes, while cocoa and chocolate have been linked with reduced oxidative stress, inflammation, and insulin resistance—all 3 of which are associated with diabetes.
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The Research

A team of researchers from Harvard Medical School and Tokyo Medical University in Japan sought to connect the dots between cocoa, chocolate, and diabetes.¹ The made use of data collected through The Physician's Health Study I and The Physician's Health Study II, 2 long-term, large-scale observational studies that followed a total of ~37,000 male physicians for as many as 32 years. The data gathered through those studies included yearly dietary questionnaires as well as information regarding health, physical activity, demographic information, and height/weight.

The researchers were able to determine which participants developed diabetes over the course of the study and compare the reported chocolate intake of those participants with that of those who did not develop diabetes.

The Results

After taking into account such factors as age, body mass index, level of exercise, and intakes of certain foods (including whole grains and nuts), the researchers initially found an inverse relationship between chocolate intake and risk of developing diabetes: those who ate more chocolate were less likely to develop the disease. Upon closer analysis of different subgroups of the participants, however, they found that only those men who were under 65 and of clinically normal body mass index actually enjoyed this reduced risk: the effect disappeared for those who were overweight or over 65.

What’s the “Take Home”?

This is a good example of needing to use caution in interpreting the results of research. Observational studies like these don't prove that one thing causes another—they show that when one thing happens, another thing also happens a certain percentage of the time. In this study, those who were younger and of normal weight were less likely to develop diabetes—and that's not surprising, statistically speaking, regardless of how much chocolate they might have reported eating. The other problem is that it was impossible to tell what kind of chocolate the participants ate. Dark chocolate? Milk chocolate? Chocolate with nuts? Chocolate spreads like Nutella? This study is interesting and adds to our knowledge that cocoa is good for you, but it's not conclusive. Sorry, chocolate lovers.

Reference:

1. Matsumoto C, Petrone AB, Sesso HD, et al. Chocolate consumption and risk of diabetes mellitus in the Physicians’ Health Study. Am J Clin Nutr 2015;101:362-7.