A recent study by experts from Harvard University, the University of Eastern Finland and Mexico’s National Institute of Public Health shows that a high egg intake may increase the risk of type 2 diabetes – but only if you live in the United States. The study, published in British Journal of Nutrition, investigates reported links between egg consumption and type 2 diabetes. It finds that eggs were only shown to be a risk factor for diabetes in the US, where eating eggs has often been associated with unhealthy lifestyle habits.

The scientists analysed the findings from ten different population-based studies from around the world – covering approximately 250,000 people (173,000 women and 77,000 men). Four of these studies were conducted in the US, one was carried out in Japan and the rest took place in Europe. During the studies’ follow-up, approximately 12,000 people developed type 2 diabetes.

The meta-analysis of existing studies and data shows that every egg added to the daily diet increases the risk of type 2 diabetes by 13%. However, there is significant variation between different countries, and the increased risk was mainly observed in the four studies conducted in the US.

A summary of the data from other countries did not reveal any association between eating eggs and the risk of type 2 diabetes. Furthermore, when the scientists looked at the seven most high-grade studies, which used data from medical registers rather than relying on participants’ self-reporting of health problems, no association was found between eggs and diabetes either. The three studies that were excluded from this higher grade analysis were conducted in the US.

As there is no clear biological explanation for the observed country-specific differences, one possible explanation the scientists put forward for these conflicting findings is that the higher risk in the US studies may be due to other factors than eating eggs. In the US studies, for example, eating eggs was often associated with unhealthy lifestyle habits such as smoking, low levels of physical activity, or frequent consumption of processed meat. Moreover, the scientists suggest that the diagnosis of diabetes may be less reliable than in studies conducted in other countries, because of the way data was gathered.

“We found evidence that results may be driven in part by studies conducted in the USA and by studies of a lower quality,” the scientists conclude.

This article is freely available for 2 weeks: Egg consumption and risk of incident type 2 diabetes: a dose-response meta-analysis of prospective cohort studies
Martha Tamez, Jyrki K. Virtanen, Martin Lajous


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