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Does more protein increase the chance of diabetes?

According to Dutch research, every 10 g protein you consume each day increases your chance of developing diabetes by 16 percent. "In the light of our results it is still unclear whether high-protein diets are favourable", says the researcher on the UMC Utrecht website. [ 18 march 2011] [Offline] "It appears that these types of diet have an unfavourable influence on sugar metabolism."

Does more protein increase the chance of diabetes?
The researcher recently received her PhD, and the part of her research on the relation between protein intake and diabetes had already been published in 2010 in Diabetes Care. [Diabetes Care. 2010 Jan; 33(1): 43-8.]

The abstract of that article is as disturbing as the UMC Utrecht press release. "During 10 years of follow-up, 918 incident cases of diabetes were documented", the Dutch researchers write. "Diabetes risk increased with higher total protein (hazard ratio 2.15 highest vs. lowest quartile)."

If you go on to read the whole article, however, you'll discover some interesting things. The research is based on an epidemiological study in which the researchers followed 38,000 Dutch people for 10 years. They divided the subjects according to their protein intake into 4 equal-sized groups, called quartiles. The group with the lowest protein intake ate 64 g protein daily, and the group with the highest protein intake managed 88 g.

And indeed, the chance of developing diabetes was twice as high in the group with the highest protein intake than in the group with the lowest intake. But epidemiologists always clean their data as much as possible first. Perhaps the people in the highest quartile are also fatter. Because fat people develop diabetes more often, epidemiologists correct for this factor. The same goes for physical activity, smoking, fruit and vegetable intake and other factors. The table below shows that the increased risk of diabetes has disappeared by the time the researchers have finished correcting.

Does more protein increase the chance of diabetes?

Does more protein increase the chance of diabetes?
In big epidemiological studies like this, if the P comes out at greater than 0.05 then you haven't found anything. And that's the case in this study too. There is no relationship between protein intake and diabetes.

What happened in the abstract for this study is not usual. As an epidemiologist you are supposed to present your corrected relationships, not rough correlations. We don't understand why these Dutch researchers did things differently in this case.

That the risk of diabetes increases by 16 percent with every 10 g protein you ingest is a calculation based on the raw research data that was collected. Because there is no relationship between the clean data and the risk of diabetes we honestly wonder whether the calculation is even methodologically correct. We are of course just ignorant journalists, but we are curious what a methodologist would make of this.

Apart from this our common sense tells us that there's no relationship between protein intake and diabetes, so there's no cause for concern about high-protein diets. If every 10 g protein did indeed increase the risk of diabetes by 16 percent then there would be an awful lot of diabetic bodybuilders and power lifters in the world. And you need a really strong searchlight to find them.

Diabetes Care. 2010 Jan;33(1):43-8.

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