Dispelling nutrition myths, ranting, and occasionally, raving


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Can eating chocolate reduce your risk of developing type 2 diabetes?

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A recent study in the British Journal of Nutrition reportedly showed that regular consumption of chocolate could reduce the risk of developing type 2 diabetes. Naturally, I wondered if that was really what the study showed.

Looking at the study, there were a few things that stood out to me. The research was done using a food frequency questionnaire, a notoriously inaccurate measure of diet. Besides the fact that this measure is often inaccurate, is the fact that we couldn’t tell if it distinguished between types of chocolate consumed. While the authors made much of the potential link between polyphenols in chocolate and reduced risk of T2 diabetes, we don’t know if the study actually looked at types of chocolate that were rich in polyphenols. By the article, we can’t tell if they made any distinction between dark chocolate, milk chocolate, white chocolate, chocolate bars, chocolate cake, chocolate ice cream, and so on. Without accounting for different types of chocolate (many of which contain negligible quantities of polyphenols) there’s no way to attribute the reduced risk of T2 diabetes to the consumption of polyphenol-rich chocolate.

Perhaps more importantly though, there’s no way we can draw any conclusions regarding causation. This wasn’t a longitudinal study so we don’t know if people who have T2 diabetes are avoiding eating chocolate (quite plausible) or if there’s some other reason why people who eat chocolate are less likely to have T2 diabetes than people who don’t.

I also wondered about the true significance of the results. For that I consulted with my math expert, Scott. His take was that the sample size wasn’t very large and that it was limited to Luxembourg. This makes it difficult to generalize the results to populations outside of Luxembourg, for example, North America, as there could be other differences between Canadians and Americans and Luxembourgians (is that the right term?) that would make it impossible to apply the findings to our population.

He also said:

Although they followed proper testing and analysis, I’d be concerned about variables that they did not include in this study, such as location and what might be in their environment or particular diet (food items not mentioned) that may distinguish this sample from say a sample in North America. I am also wary anytime the analysis includes a questionnaire or feedback rather than pure conclusions based on observed tests and results. As you well know from interviewing people at stats can, there are more than admitted “fake” stats and responses… Yes, I do see a correlation between the two, I would require further testing to be conclusive on the hypothesis.

I followed up this analysis by asking him if he thought the standard deviations were of concern. To my untrained eye, I thought that it was possible that the range for each result was large enough that there might, in actuality, be no real difference between each group. Scott said:

I would support that claim, you would want the SD to be much closer to the mean than those results. I suspect the SD would fluctuate with any other sample size tested under those conditions.

And there you have it. While it’s possible that there’s a reduced risk of having diabetes to chocolate consuming Luxembourgians, there’s more research to be done before anything definitive, especially for other populations, can be concluded.


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A closer look at the full-fat dairy prevents T2 diabetes study

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Image by Roey Ahram on flickr. Used under a Creative Commons Licence

Findings of a study suggesting that full-fat dairy products might be protective against the development of T2 diabetes hit the news recently. Of course, you know me, I was curious if the research was sound.

One of the primary authors holds a patent for the use of trans-palmitoleic acid (one of the common fatty acids in dairy products) for the prevention and treatment of insulin resistance, type 2 diabetes, and related conditions. Right off the bat, there’s a red flag as it stands to benefit the author if he can support the assertion that high-fat dairy (or at least one fatty acid in dairy) can treat T2 diabetes.

I thought that it was interesting that they chose to use circulating fatty acid biomarkers as determination for consumption of full fat dairy products. This sounds like a better idea than the typical self-reported food frequency questionnaire. However, I wondered how accurate such a measure is. It seems that I wasn’t the only one with such a concern. When I searched to find out the accuracy of the use of such biomarkers I came across a letter to the editor expressing concern that some of the FA biomarkers used could also be attributed to fish consumption. Some of the FAs used in this study can also come from other meats, so may not all be attributable to dairy consumption. It seems that there are some additional limitations to use of biomarkers in research as lifestyle and disease state factors may affect metabolism and the resulting presence (or absence) of such biomarkers. Essentially, while the use of biomarkers may seem objective, they may not tell the full story. I also question how long biomarkers such of these remain present in the blood following consumption of dairy foods. Would they be indicative of long-term diet patterns or simply of having recently consumed high-fat dairy? Not being knowledgable in the area of biomarker research I can’t answer this question so it may or may not be worth raising.

Importantly, to account for potential confounding variables, the researchers used self-reported physical activity and food frequency questionnaires. Thus, there is always the potential that there might be another cause for the development (or prevention) of T2 diabetes in study participants.

There are also concerns regarding the actual study participants. The researchers used participants in the Nurses Health Study and the Health Professionals Follow-Up Study. These participants, health professionals, may not be reflective of the general population so generalization of the results to all Americans, or those in other countries is not necessarily possible.

I’m also not convinced that, while statistically significant (where is my personal statistician?*), the results hold any real-life meaning. The number of cases of T2 diabetes diagnosed in all study participants wasn’t huge so a 36-44% risk in reduction, while sounding massive, might not translate to a huge decrease in risk in actuality.

*After writing this, I had a friend with an advanced math degree offer to take a look at the original research for me (thanks Scott!). Here’s what he had to say:

My only concern with the data is the sample size of 3,333 which is not that large considering the amount of variables that they are accounting for. More variables the more likelihood of outliers that may not be actual outliers, but the sample size is so small it appears that way. However, they seemed to have introduced enough controls in their testing to reduce the risk.

What does all this mean? Basically, don’t go crazy on high-fat dairy products just yet. However, as you should only be eating a couple of servings of dairy a day anyway, you should go with foods that you enjoy. Why not have a variety of foods; maybe low-fat milk on your cereal, but full-fat yoghurt for a snack? Variety is the spice of life.