Which Came First -- The Egg or the Diabetes?

Men who ate more than five eggs a week had a lower risk of developing type 2 diabetes than men who ate about one a week only, according to researchers in Finland.

In a study with an average follow-up of almost 20 years with 2,332 participants, researchers noticed that those in the highest quartile for egg intake had a lower risk of developing diabetes than those in the lowest quartile (hazard ratio 0.55, 95% CI 0.38-0.79; P=0.001) when cholesterol and other factors were controlled for. Four hundred and thirty two men were found to have developed diabetes.

"These findings suggest that the recommendations to limit the consumption of eggs (or any food) in a general health population should not be based on a single component in food, such as the cholesterol in eggs," wrote the authors, led by Jyrki Virtanen, PhD, an adjunct professor at the University of Eastern Finland. They published their results last week in The American Journal of Clinical Nutrition.

The baseline data were gathered from 1984 to 1989 as part of the Kuopio Ischemic Heart Disease Risk Factor (KIHD) study. The first cohort of men were 54 and enrolled from 1984 to 1986; the second were 42, 48, 54, or 60 years old and enrolled from 1986 to 1989. In the analysis, those with type 2 diabetes at baseline, those with impaired fasting glucose, those whose diabetes status was unknown, or those who were missing data on dietary intake were excluded.

Diabetes status was identified by questionnaires as well as by an oral-glucose-tolerance-test blood glucose measurement and a review of hospital and reimbursement registries. Dietary intake was self-reported over 4 consecutive days. Participants were given instructions and a guide with pictures to help them determine portions.

Yunsheng Ma, MD, an associate professor of medicine at the University of Massachusetts Medical School, said in an email to MedPage Todaythat the study "provides welcome news to support the 2015 dietary guidelines, which are expected to drop the limit of egg consumption for blood cholesterol concerns."

Ma said that he was aware of six studies that examined egg consumption and diabetes. One showed an increased risk, he said, and the other five showed no association. "So these results are not in line with other findings," wrote Ma. "More studies will be needed to confirm these findings from the current study."

Virtanen also added that the findings should be relevant to dietary advice. "I think this study is a good example that we can't very convincingly predict how a certain food is associated with the risk of disease based on a single nutrient in that food, such as cholesterol in eggs," he wrote in an email to MedPage Today."Therefore, more research should, and has started to, focus on whole foods and food groups instead of isolated nutrients."

Ma said that eggs provide high quality protein and are a good source of several vitamins, minerals, and fatty acids. "For clinicians and dietitians, I think moderate consumption of eggs should be encouraged in the general population," he wrote. "Eggs, whole grain, fruits, vegetables, and lean animal and vegetable protein should be included as part of the healthy diet."

In the study, at baseline, men who had a higher egg intake were more likely to be younger, have higher serum apolipoprotein A-I concentrations, have lower serum triglyceride, and less likely to smoke, have ischemic heart disease, and hypertension. They also ate more red meat, dairy, linoleic acid, fiber, coffee, and cholesterol, said researchers. The average intake for eggs was more than half a medium egg per day (33 g/d), and only 22 participants didn't have any eggs at all.

The researchers analyzed two other models. The first was adjusted for age, examination year, and energy intake only. In that analysis, those in the quartile who ate the most eggs -- more than 45 grams a day, or a little less than one egg per day -- were also less likely to develop incident type 2 diabetes (HR 0.63, 95% CI 0.47-0.83;P>0.001).

The second model controlled for the factors in the first, in addition to family history of diabetes, hypertension, smoking status, education, leisure-time physical activity, percentage of all serum fatty acids, alcohol intake, and diet.

Though the study was investigating men from Eastern Finland only, Virtanen said he thinks the results are generalizable. Some studies have found a higher risk of type 2 diabetes with a higher egg intake or have found no effect of egg intake on diabetes at all. But he noted that in the studies, those with a higher egg intake "also tended to have more unfavorable lifestyle and dietary factors, e.g., they smoked more or were less physically active, and this was not found in our study."

In addition, "In many countries it is common to eat eggs with processed meats, such as bacon, and processed meats have been shown to increase the risk of type 2 diabetes," he wrote. "In Finland eggs are commonly eaten as such on a piece of bread or as a part of a mixed dish, not with processed meats like bacon."

Limitations of the study included that it didn't look at how the eggs were prepared, though researchers did take into account eggs eaten as part of a larger dish. Only a few participants ate egg whites only, so researchers could not tell if there was a difference between eating egg whites and whole eggs.

In addition, the single baseline measurement may have not been long or accurate enough, and may have led to random error, said the researchers.

Read more at MedPage Today.