This past weekend, amidst all the Ancestral Health Symposium madness, I caught the headline while flicking through my phone for a few brief seconds. Didn’t open it up, though. Just cruised on past. I’d hoped to just forget about it, to ignore it, to banish it to the back of my mind where half truths and junk studies go to die. And truth be told, I pretty much had forgotten about it until I checked my email to find a ton of frantic emails from readers wondering if their beloved and dependable egg yolk breakfasts were killing them faster than the cigarettes they don’t smoke. What? You didn’t hear?
Followed by (with less hysterical capitalization) “May increase carotid plaque build-up.”
So what are we looking at here?
We’re looking at a study in which a trio of researchers (two of whom with extensive ties to the statin industry) quizzed a group of middle-aged and elderly stroke patients about their lifelong egg intake and smoking history, making sure to stress the importance of accuracy and honesty in their answers. Yes, you heard me right: they expected people to remember every last egg they ever ate. Still, everyone in the study was assumed to have supernatural memory, so I guess it evens out.
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.
Those who ate the most eggs also smoked the most and were the most diabetic. To their credit, the authors tried to control for those factors, plus several others. Although they tried to control for sex, blood lipids, blood pressure, smoking, body weight index, and presence of diabetes, the study’s authors didn’t – couldn’t – account for all potentially confounding variables. In their own words, “more research should be done to take in possible confounders such as exercise and waist circumference.” Hmm. “Possible” confounders, eh?
Exercise reduces thickness of the carotid arterial wall. It doesn’t get much clearer than that. Exercise is a massively confounding variable that the authors failed to take into account.
What about waist circumference?
Or how about stress, which also wasn’t considered?
Yeah, it’s not like the size of a person’s waist, whether or not they move of their own volition or sit in an easy chair all day, and how much stress they endure have any impact on their risk of developing atherosclerosis. Those things may be linked, and I’m sure the authors would have loved to include them in their analysis, but there just wasn’t enough space on the questionnaire. Besides, it’s not like a little physical activity and mediation could even undo the damage wrought by 4.68 sinful egg yolks per week. Why, that’s nearly a half dozen!
Seriously, though, the subjects were all stroke patients who’d lived to tell the tale. They’d been in contact with the medical community (you generally don’t just shake off a stroke without medical attention), who no doubt gave them the standard required advice to prevent another event, which includes “a reduction in saturated fat and cholesterol intake…and a boost in physical activity.” Since the egg-eaters obviously didn’t listen to their doctors’ recommendations to cut back on cholesterol intake, I’d wager they treated the exercise recommendations with similar levels of disdain. What do you think?
Here’s what I think: this is an observational study whose already limited worth depends entirely on the memory of an inherently fallible creature being infallible. As such, it cannot assign causality, contrary to what the media (“Egg Yolks Can Quicken Hardening of the Arteries“) and authors (“It has been known for a long time that a high cholesterol intake increases the risk of cardiovascular events”) say. Furthermore, why single out egg yolks? I mean, I get it – the authors sort of have a vendetta against eggs – but what about other foods? Were those even analyzed or asked about? What about the stuff that people generally eat with eggs, like pancakes and vegetable oils, or the foods that contain egg yolks, like baked goods and mayonnaise? For all we know, egg yolk intake could have been a marker for eating garbage; most people aren’t tossing raw yolks into post-workout shakes, gently poaching eggs with coconut vinegar, or horrifying co-workers with a bag full of hard-boiled eggs like we Primals are wont to do. They’re getting Grand Slams at Denny’s, eating bologna sandwiches with mayo on white bread, and overcooking scrambled eggs in canola oil until they’re rubber.
For fun, though, let’s look at what some other studies have found with regards to the artery-clogging capabilities of whole eggs:
Egg consumption and endothelial function: a randomized controlled crossover trial. Two eggs daily did not impair endothelial function (the flow of blood through the arteries), nor did it increase total or LDL cholesterol. Overall, eating two eggs a day elicited no change in cardiovascular health when compared to eating oatmeal (a cardiologist’s pride and joy).
Daily egg consumption in hyperlipidemic adults – effects on endothelial function and cardiovascular risk. In patients with high cholesterol, eating several hard-boiled eggs a day had no effect on endothelial function.
Effect of a high-saturated fat and no-starch diet on serum lipid subfractions in patients with documented atherosclerotic cardiovascular disease. Obese patients with heart disease ate lots of saturated fat, zero starch (including zero grains – sound familiar?), and tons of vegetables, and saw massive weight loss without any negative effects on their blood lipids. Once upon a time, I had access to the full study (it was freely available at the website for the Mayo Clinic, who’s since taken it down…wonder why), and I remember seeing that they ate three or four eggs a day. If egg yolks were bad for all heart disease patients, these guys would have felt the effects.
Okay, despite all those confounders and other egg studies that support yolks as harmless and the fact that this was merely an observational study without the power to assign causation and whose authors failed to even propose a potential mechanism of action, let’s entertain the notion that something was going on with this population of egg eaters. What if the egg yolks did have something to do with the atherosclerosis?
In a previous post on “Human Interference Factor,” I highlighted a study showing hens given an unnatural industry-standard diet high in omega-6 containing grains (soy and corn) produce less healthful eggs than hens on a more natural diet of grains lower in omega-6 with supplementary antioxidants. When subjects ate two of the soy/corn-fed eggs a day, which were high in omega-6 fats, their oxidized LDL levels were increased by 40%. Subjects who ate two of the other eggs each day, which were low in omega-6 fats, had normal levels of oxidized LDL (comparable to subjects in the control group, who consumed between two and four eggs a week). Since the oxidation of LDL particles is strongly hypothesized to be a crucial causative factor in atherosclerosis, it’s conceivable that eating normal, industrial eggs could have a negative effect on carotid plaque.
Anyway, what are the takeaways here?
Exercise, practice stress reduction, and get your waist circumference checked.
Don’t pay too much attention to ridiculous observational studies (this is part of stress reduction).
Oh, yeah – eat egg yolks, and lots of them. Doubly so if you’re low-carb (remember the starch/grain-free high-egg diet referenced above). Make ’em pastured, if possible, or at least from hens that ate something besides soy and corn. They’re more nutritious and probably “safer” than industrial eggs.
(In retrospect, that mention of the authors’ ties to the pharmaceutical industry was a low blow. After all, I myself am a direct benefactor of my local pastured egg industry; they pay me in delicious golden yolks.)
I hope you found this post helpful. Have at it in the comments.