Opinions differ on latest egg yolk science

Thursday, August 16, 2012

by BETTER FARMING STAFF

Asked in an email if he had anything good to say about eggs yolks, David Spence said whites are fine and then he added, “My mother used to say we should give the yolk to the cat; it made her fur shiny.”

Spence, now professor of neurology and clinical pharmacology, Western University, and director of the Stroke Prevention and Atherosclerosis Research Centre at the Robarts Research Institute, would probably agree with his mother’s advice. His latest research paper, Egg yolk consumption and carotid plaque, appeared this week in the journal Atherosclerosis and it pretty much puts the egg yolk in the cat’s dish, comparing the damage caused by egg yolks to the damage caused by cigarette smoking.

Researchers used ultrasound to measure plaque buildup on the arterial walls of  1,231 patients attending vascular prevention clinics at London Health Sciences Centre's University Hospital. The average age of those studied was 61.5 years although the range was 40 to 80 plus. They found an increase in plaque buildup for people after age 40. However, there was an exponential rise for smokers and regular egg-yolk eaters. The buildup rate for egg-yolk eaters was two-thirds the rate for people who are smokers. There was only one ultrasound measurement taken at whatever age the patient presented.

The question is, was the culprit the egg yolk or the bacon or butter or Danish that went with the egg? Spence answers, “All we say is that the effect of egg yolk was independent of sex, blood pressure, serum cholesterol, diabetes and body mass index.” In the paper itself, Spence et al, allow that the study weaknesses include “its observational nature, the lack of data on exercise, waist circumference and dietary intake of saturated fat and sources of cholesterol other than eggs, and the dependence on self-reporting of egg consumption and smoking history, common to many dietary studies.” In fact, Spence says “all dietary studies are based on questionnaires; they’re all self-reported.”

Spence says everyone is at risk of cardiovascular disease if they live long enough. One of Spence’s critics believes age may have more to do with arterial plaque formation than anything.

Author, blogger and nutritionist Zoe Harcombe devoted her August 8 blog to refuting Spence’s egg-yolk research. Looking at one of the tables in the study, Harcombe notes it shows an increase in arterial plaque from the youngest to the oldest. “I look at the above table and conclude that the strongest relationship  is between age and plaque, as one would expect.” She adds, “The authors could have picked broccoli” and gotten the same result.

Spence, on the other hand, argues with research used by “egg marketers,” including the Harvard study of health professionals and a latter population-based study.

“They took a bunch of young people and did questionnaires and then followed them,” Spence says. “Take a 25-year-old and follow him for 20 years, that’s not enough . . . The same studies showed that, among people who became diabetic, an egg a day doubled coronary risk.”

In a news release following the online publication of the study, Spence said, “What we have shown is that, with aging, plaque builds up gradually in the arteries of Canadians, and egg yolks make it build up faster, about two-thirds as much as smoking.”

Karen Harvey a registered dietitian and the nutrition officer for the Egg Farmers of Canada (EFC), says the smoking/egg-yolk comparison “is not a valid one. Smoking is widely considered one of the most harmful activities when it comes to personal health and wellness. We know that eggs are one of nature’s most nutritious foods.”

Harvey says EFC will continue to reference Harvard University studies which found no connection between heart disease and egg consumption. “They looked at those who consume one egg or less per week verses those who were eating seven or more eggs a week and they found there was no difference in their risk for heart disease or stroke.”

A 2011 Harvard University medical school study followed 21,327 physicians for 20 years and found no connection between egg consumption and heart disease or stroke, except in diabetics where the risk doubled for those eating seven or more eggs a week compared with less than one. - BF