Egg yolks are bad for you?!?

4 09 2012

Spending several years in a medical setting, I have become acquainted with reading research studies and identifying the conclusions and ramifications – even if they are not completely the same as those published by the authors in the paper.  There has been a study discussed in the news recently that has piqued just this interest in me – perhaps you have heard of it: “Egg yolk consumption and carotid plaque.”

In this study, published in the journal Atherosclerosis, Spence and his colleagues wanted to examine the link between egg yolk consumption and atherosclerosis.  The authors point out that this has, for some time, been a controversial issue, with previous studies falling on both sides of the debate – some state that eating egg yolks raises serum cholesterol while other studies saw no change.  In an effort to identify whether or not eggs are, in fact, deleterious to cardiovascular health, Spence, Jenkins, and Davignon decided to look at a different marker in examining risk for cardiovascular disease: total plaque area.

That’s a lot of science to start out this article, so I’ll back track a little bit.  While we might debate its validity, cholesterol is still a leading indicator for risk of cardiovascular disease and coronary heart disease.  Generally speaking, cholesterol values can be broken down into high-density lipoprotein (HDL – “good” cholesterol) and low-density lipoprotein (LDL – “bad” cholesterol).  As LDL increases as a proportion of total cholesterol (or often times as a ratio compared to HDL and/or triglycerides), the risk for disease increases.  Because the effects of egg yolk consumption on cholesterol have been equivocal up to this point, the authors must have wanted to use a different variable, hence measuring total plaque area.  

So why did this study get me worked up?  Firstly, it was the inflammatory headline that ran on CNN: “Egg yolks as fatal as cigarettes”.  Secondly, when I sat down to read the study, the authors made some pretty broad generalizations and gross over simplifications.  To start with, in order to identify egg yolk consumption over time, the authors culled information from “lifestyle questionnaires” from patients “at the time of referral” to a vascular prevention clinic after transient ischemic attacks or strokes.  Simply put, the authors asked patients how many eggs they had eaten through their lives on a questionnaire.  These were patients who had already had an transient ischemic attack or stroke (A transient ischemic attack – or TIA – is when blood flow to a part of the brain stops for a brief period of time. A person will have stroke-like symptoms for up to 24 hours, but in most cases for 1 – 2 hours.  A TIA is felt to be a warning sign that a true stroke may happen in the future if something is not done to prevent it.).  Inferring anything about lifestyle or dietary habits of healthy individuals based on the presentation of sick individuals is extremely confounding and usually not very accurate because of physiological changes brought on by the disease process.

The other problem with how Spence and his colleagues collected the data was with their dietary recall.  The average age of the subjects in the study was 62; how was someone expected to remember how many eggs they had eaten throughout their life, let alone even what they ate last week?  As fitness professionals, we are intimately tuned into our nutrition, but I for one, can’t even recall what (let alone how much) I ate last month.  Additionally, egg consumption was the only dietary variable that the authors examined.  I would highly doubt that most people eat eggs in isolation of other foods, and for that matter, wouldn’t these other foods possibly contribute to – OR – take away from accumulation of plaque in the arteries?

OK so those are the fatal flaws of the study on it’s surface.  What next?  The authors wanted to relate any atherosclerosis brought on by egg consumption to previously known plaque producers.  So what did they do?  They compared eating eggs to cigarette smoking!  How are these two habits AT ALL comparable?  One habit is a known carcinogen, destroyer of lung tissue, and HIGHLY addictive.  The other, however, is a complete food uniquely designed to sustain life.  Can you tell which one is which?

If you’re still keeping up, the authors showed that increasing egg consumption ran almost parallel to cigarette smoking with regard to accumulation of arterial plaque, with both showing a direct exponential relationship as consumption (or smoking frequency) increased.  WOW!  So maybe eggs are pretty bad for you huh?  The general consensus that we, as a staff, drew from this study was that it really only relates to those already at risk for coronary heart disease and/or strokes.  We make recommendations to clients with respect to their nutrition and eating habits for improving their health and fitness.  We do need to keep this study in mind when making those recommendations, but for the vast majority of our clients who have not experienced a cardiac episode or stroke, or are at risk for them, this study is not all that relevant.

What does this mean for all of you?  Keep eating those eggs!  Eggs contain a multitude of vitamins, minerals, and other micronutrients that are hard to come by from other foods (choline anyone?).  Additionally, they are a great source of easily digestible protein needed for recovery from workouts and keeping the body health.  While eggs do contain cholesterol (about 200mg per egg) your body NEEDS cholesterol to function properly.  Everybody needs cholesterol to maintain a healthy balance of all number of hormones, including the sex hormones, which many researchers believe are important for maintaining vitality.  Do, however, make sure that these eggs are part of a healthy meal full of ripe brightly colored fruits and vegetables.  And be sure to peruse the archives of the blog, as there are several great tasty egg recipes throughout.

If this got you all worked up over egg consumption, check the following rebuttals to learn more about it from very well informed scientists, researchers and nutrition consultants:

Mark’s Daily Apple

Zoe Harcombe

Outside Magazine

Chris Masterjohn (Weston A Price)


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