Dispelling nutrition myths, ranting, and occasionally, raving


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More biased research on the wonders of walnuts

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The California Walnut Board’s been busy lately. The latest study funded by them, to be published in the June issue of The Journal of Nutrition, found that consumption of whole walnuts and walnut oil had a positive effect on blood vessel function following a meal as well as improving the effectiveness of HDL (the “good” cholesterol). This is all lovely but I have a few questions.

I wonder how walnuts and walnut oil fare in comparison to other nuts and oils. I also wonder if there are any long-term implications for these findings. A short-term effect of consumption of a food, both positive and negative, means little in the big picture. Sure, it may very well be true that consumption of walnuts improves cardiovascular health but such a small study (only 15 participants) over such a short period of time: 30 minutes, one hour, two hours, four hours and six hours after administration of treatments really doesn’t tell us much about the impact of walnut consumption on long-term health.

I complain about unscientific practices a lot but science like this is just as bad. Give me a large, long-term, double-blind, study with unbiased researchers and then we can talk about the miracles of walnuts.


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Don’t go too nuts for walnuts

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I’ve been seeing a few news reports recently regarding nut consumption, particularly walnuts, and diabetes. The reports are based on a study Walnut Consumption Is Associated with Lower Risk of Type 2 Diabetes in Women. This study used data from the Nurses’ Health Study to determine the effect of nut consumption on diabetes risk.

The news article all proclaim that regular consumption of walnuts can reduce the risk of developing type 2 diabetes. There was a risk reduction shown with consumption of walnuts as little as once a month but the greatest risk reduction (24% in comparison to women who ate few or no nuts) was seen in the women who ate walnuts at least once a week.

Now, as much as I’m a fan of nuts, I’m always a little skeptical of reports such as this. I always wonder if the news reports accurately reflect the study’s findings and if the study is well-designed. So… I went and took a look at the journal article.

I’m immediately wary of any study that uses food frequency questionnaires to obtain data on food consumption. These questionnaires are notoriously inaccurate. Putting that issue aside and looking at the rest of the study, a couple of additional issues popped out at me. While the researchers controlled for things such as physical activity, fruit and vegetable consumption, and obesity, it is impossible to control for all variables and it’s possible that a factor common to the walnut eating group other than their walnut consumption may have reduced their risk of diabetes. Also, after controlling for BMI, the risk reduction afforded by walnut consumption dropped from the reported 24% to 15%. Perhaps if another measure, such as waist-to-hip ratio had been used this percentage would have decreased further.

Most importantly: funding for the study was provided by the California Walnut Commission.

I certainly don’t want to discourage anyone from eating walnuts. However, too much of any one thing can be bad for us and I don’t want anyone reading reports from this study erroneously thinking that they should be consuming unlimited quantities of walnuts to stave off type 2 diabetes. There are benefits to all nuts and they all contain fairly concentrated calories so it’s certainly possible to go overboard with them. Incorporate a variety of nuts in your diet to obtain the maximum health benefits from their consumption.