We all know that eggs contain a lot of fat and cholesterol. While that does not make them “bad,” most of us realize that if you eat eggs or any other food to excess you will likely suffer some negative health effects. But are egg yolks as bad as cigarettes for heart health? That’s question that’s been making headlines in recent months after the publication of a study that asserts this idea. Unfortunately, most of journalists reporting on the story did not bother to actually read the paper, which has major flaws that cast serious doubt on the conclusion -- something the authors of the paper note when they call for further study into their hypothesis.
Yet the presses roll on, leading a lot of readers to question whether or not they should change their diet based on what seems like new data. Even more worrying than individuals altering their eating habits is the likelihood that politicians could use this study as justification for any number of hare-brained schemes to improve the health of Americans.
Published in the Journal of Atherosclerosis, “Egg yolk consumption and carotid plaque,” was authored by three Canadian physicians motivated by an increasing lack of regard for the role that dietary fat and cholesterol play in the development of coronary heart disease, according to the paper’s introduction. They looked at nearly 3,000 people, all of whom they found at vascular prevention clinics in Canada, and asked them about their egg consumption and cigarette smoking. Over the years, they tracked these participants and found that “egg yolk years” -- that is, the number of eggs eaten per week times the number of years in the study -- are correlated with increasing plaque in the carotid arteries. They found that the egg yolk year-to-plaque correlation was similar to the cigarette-plaque correlation.
There are numerous problems with this study. First, the research was based on yearly self-reporting from patients. Self-reporting is notoriously inaccurate (can you remember how many eggs you ate last year?). There is also the major issue that all of the participants were patients at vascular prevention clinics -- which one can assume means they either already have vascular problems or are at high risk as a result of genetic or lifestyle risk factors. As SUNY professor and biochemist Richard David Feinman put it, “this is a limitation of many nutritional studies and, while a source of error, it is depends on how you interpret the data.” But that brings me to what I see as the biggest problem in this study: the limited data the researchers chose to examine and draw conclusions about. The researchers did not track other foods the participants ate (maybe they always ate toast and bacon with their eggs) nor did it take account of activity level or exercise.
What they found in their research is that “egg yolk years” correlated with plaque build-up in carotid arteries -- in a similar fashion to cigarette smoking. Based on the authors’ premise, one would have expected cholesterol to rise with egg consumption as well. But this is not what the study’s data show. They show no relationship between egg yolk consumption and serum cholesterol. As “diet guru” Zoë Harcombe noted:
For this study to suggest an association between egg yolks and carotid plaque (which is analogous for heart disease in effect in the article) there needs to be a plausible mechanism. Interestingly the study has ruled out cholesterol as a mechanism. Hence the conventional view that cholesterol is ‘clogging up arteries’ cannot be used because no association with cholesterol holds.
In fact, it seems that the strongest factor that correlated with plaque buildup was time. As fitness author Mark Sisson noted of the study:
Those who ate the most eggs were the oldest – almost 70 years old on average, compared to the relatively sprightly 55 year-old egg avoiders. It’s pretty well accepted that with age comes the progression of atherosclerosis, a process that takes, well, time to occur. Plaque doesn’t just snap into existence; it develops. All else being equal, the older you get, the more plaque you’ll have.
The authors of the study didn’t talk a lot about the lack of a relationship between cholesterol and egg consumption, which is good because most of the research in the last 15 years has pointed toward other causal factors in heart disease. Where doctors once took it as gospel truth that eating fat and cholesterol caused one to be fat and have high cholesterol, researchers now believe inflammation, caused by numerous factors, is the cause of heart disease with raised cholesterol as a symptom:
Excessive free radicals created by high blood pressure, diabetes, cigarette smoke, fatty meals, elevated insulin levels with oxidized LDL cholesterol, elevated homocysteine, and possibly some infectious agents have the capability to cause inflammation of the surface lining of the arteries called the endothelium. This either causes an actual tear of the endothelium or causes the endothelium to function abnormally. LDL cholesterol is then allowed to enter into the subendothelial space (area just under the lining of the artery) where it becomes oxidized and starts to build a plaque. The cholesterol actually comes along as a band-aid trying to repair the damage to the artery caused by inflammation. This is what creates hardening of the arteries.
It might come as a shock to a few readers that dietary cholesterol does not go straight into your arteries, just like dietary fat does not instantly get transferred to your butt. In fact, even if you consumed zero cholesterol, your body would still make it anyway and your blood cholesterol would only fall by 20-25 percent.
But like I said, the authors do not seem to mind that there is no correlation between yolk eating and blood cholesterol. They bypass the glaring lack of a proposed mechanism by which yolks increase carotid plaque, as well as glazing over the possibility that other factors in the participants’ lives could correlate with increased plaque. Instead, they come to the conclusion that reducing yolk consumption is the way to reduce the risk of heart disease. To their credit, the authors at least conclude the paper by declaring the need to test their hypothesis with “more detailed information about diet, and other possible confounders such as exercise and waist circumference,” yet they still recommend that people at risk of cardiovascular disease avoid eating egg yolks.
All this study has demonstrated is that the group of people these doctors chose to look at had an increasing amount of plaque in their arteries as they got older and maintained whatever kind of diet and lifestyle they had been living prior to the study. That hardly seems like something to write home about let alone write a news story about or change your diet because of. Yet I fully expect to see policy makers declaring the need for “fat taxes” or caps on the amount of cholesterol allowed in fast foods, wielding this study as proof.
In the end we all have different dietary needs and it should be up to each individual to determine how many egg yolks they should or should not be eating for their own desired health.