Egg yolk consumption, carotid plaque & bad science
“Egg yolks linked to heart disease” screamed the headlines on Monday 6th August 2012. The newspaper article came from a journal article called “Egg yolk consumption and carotid plaque“.
I really have got better things to do than to continually dissect articles from so called scientists, but, when the item under attack is the super food called egg, someone has to leap to its defence. So here goes….
I have a copy of the full article – sadly it’s not on free view. You can see the abstract on this link. The abstract tells us that 1,262 people were involved in the study with an average age of 61.5. 47% were women. (The full article says that 1,231 participants were involved – discrepancies like this should be corrected before publication.)
The results were summarised as: “Carotid plaque area increased linearly with age after age 40, but increased exponentially with pack-years of smoking and with egg-yolk years. Plaque area in patients consuming < 2 eggs per week (n=388) was 125± 129mm2, versus 132 ± 142 mm2 in those consuming 3 or more eggs per week (n=603).”
The Canadian authors – David Spence, David Jenkins and Jean Davignon concluded: “Our findings suggest that regular consumption of egg yolk should be avoided by persons at risk of cardiovascular disease.”
The authors have invented the term “egg-yolk years”, which is defined as egg yolks consumed per week times number of years of consumption. They compare this with “pack-years of smoking”, which is defined as number of packs per day times number of years smoking. Yes – this article really does place one of the most nutritious foods on the planet alongside one of the most harmful man-made drugs – and conclude that they are just about equally evil…
“Our data suggest a strong association between egg consumption and carotid plaque burden. The exponential nature of the increase in TPA by quintiles of egg consumption follows a similar pattern to that of cigarette smoking. The effect of the upper quintile of egg consumption was equivalent in terms of atheroma development to 2/3 of the effect of the upper quintile of smoking. In view of the almost unanimous agreement on the damage caused by smoking, we believe our study makes it imperative to reassess the role of egg yolks, and dietary cholesterol in general, as a risk factor for CHD.”
These Canadian guys have been after eggs for some time – as this November 2010 article shows. Thankfully the brilliant Tom Naughton was around to respond to that one .
The entire study is about egg yolks. There is no evidence presented in the paper that these 1,231 people throw away egg whites. The paper has simply assumed that there can be nothing in egg whites that could cause any concern whatsoever so we don’t need to even think about egg whites. As someone interested in nutrition, here is the comparative nutritional information for whole eggs (which normal people eat); egg whites (which people who don’t value vitamins and minerals eat) and egg yolks (which people who do value vitamins and minerals eat).
|(All per 100g of product)||USA RDA/AI||Whole egg||Egg yolk||Egg white|
|B1 (Thiamin) (mg)||1.2mg||0.1||0.2||0|
|B2 (Riboflavin) (mg)||1.3mg||0.5||0.5||0.4|
|B3 (Niacin) (mg)||16mg||0.1||0||0.1|
|B5 (Pantothenic Acid) (mg) (AI)||5mg (AI)||1.4||3||0.2|
|Folic Acid (Folate) (mcg)||400mcg||47||146||4|
|B12 (mcg)||2.4 mcg||1.3||1.9||0.1|
|D (IU) (AI)||400IU (AI)||35||107||0|
|K (mcg) (AI)||120mcg (AI)||0.3||0.7||0|
|Calcium (mg) (AI)||1000-1200mg (AI)||53||129||7|
|Potassium (mg) (AI)||4700mg (AI)||134||109||163|
|Sodium (mg) (AI)||1500mg (AI)||140||48||166|
|Manganese (mg) (AI)||2.3mg (AI)||0.0||0.1||0|
|Selenium (mcg)||55 mcg||31.7||56||20|
So the egg yolk is where we find the nutrition in an egg. Please bear this in mind as we go on to talk about egg-yolk years alongside pack-years of smoking…
Table 2 at the end of the paper has the baseline characteristics of participants in the study (1,231 people) by quintile of egg-yolk eaters.
|Egg yolk years||<50||50-110||110-150||150-200||>200|
|Age at first visit||55.70||57.97||56.82||64.55||69.77|
|Eggs per week||0.41||1.37||2.30||2.76||4.68|
|Smoking (pack years)||14.14||14.37||16.57||13.88||17.00|
|Plaque area (mm2)||101.45||110.35||113.58||135.76||175.77|
The article notes that: “carotid atherosclerotic plaque burden increases linearly after age 40“. This means that plaque area increases directly with age – this is not surprising and by far the most obvious relationship in all of these variables. (Please note that the plaque itself is not the root cause of problems. Plaque forms over damage to the arterial walls in much the same way that a scab forms over a cut on the skin. The original source of that damage is what we need to understand. Chief suspects should be smoking, sugar, stress, chemicals and apparently we now need to add egg yolks to this list!)
The above table has columns A to E categorised into these invented egg-yolk years. The plaque area rises from columns A to E. However the age of the participants at first visit also rises from A to E. The average age in column A is under 56; the average age in column E is 70. That’s a 14 year difference! Surely the single biggest determinant of plaque area?
Column E has 24% more incidence of diabetes than column A – could that impact plaque area? (Please note that the association between plaque area and diabetes does not follow a uniform relationship – Columns C and D buck the trend).
Column E has 20% higher smoking pack years than column A – could that impact plaque area? (Please note that the association between plaque area and smoking pack years does not follow a uniform relationship – Column D bucks the trend).
The data – Plaque builds up with age
I look at the above table and conclude that the strongest relationship is between age and plaque – as one would expect.
If you consume a particular food regularly over more years you will amass more ‘food-years’. The authors could have picked broccoli and measured broccoli years and the top quintile group of 70 year olds would have had 14 years more broccoli consumption than the 56 year olds!
But when you are funded by drug companies, to continue the cholesterol/lipid hypothesis you’ll pick on a cholesterol rich food and not broccoli. Scroll down to “Conflict of interest” and you’ll see: “Dr Spence and Dr Davignon have received honoraria and speaker’s fees from several pharmaceutical companies manufacturing lipid-lowering drugs, and Dr Davignon has received support from Pfizer Canada for an annual atherosclerosis symposium; his research has been funded in part by Pfizer Canada, AstraZeneca Canada Inc and Merck Frosst Canada Ltd.”
The data – Eggs & cholesterol levels
The other thing I take from the table above is that egg consumption has bugger all to do with blood cholesterol levels – unless we want to note the inverse association. People eating an average 4.68 egg yolks per week have lower total cholesterol, lower triglycerides, higher HDL and lower LDL than people eating an average of 0.41 egg yolks per week. Omelette anyone?
However, this also doesn’t display a consistent relationship – total cholesterol is highest at the mid range of egg yolk consumption – an average of 2.3 per week. Triglycerides and LDL are also highest at the midpoint of egg yolk consumption – an average of 2.3 per week. (Not that I care about any ‘cholesterol levels’ – but just to comment on the data in the article from people who do care about ‘cholesterol levels’).
BMI, by the way, peaks at the midpoint of egg consumption and is lowest at the highest level of egg consumption. Low carbers know why.
In all of this please note that even the highest egg consumers are not eating even one egg a day. The very top egg consumers are consuming an average two thirds of an egg a day.
What plausible mechanism is there?
Any study not only has to show an association, it has to show that this association is plausible. I can observe that more people who wear blue socks have a larger plaque area than people who wear red socks. However this is a meaningless observation unless I can offer a rationale for why this might be.
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 (the association is inverse, if anything).
So what is the mechanism by which egg yolks are supposed to build carotid plaque? We don’t know. The article is conspicuously silent on any possible pathway, let alone any plausible pathway.
Let’s see what happens when we eat to see how ludicrous this study really is…
One large egg yolk (c. 17g) has 9g water, 3g protein and 5g of fat – the majority of the fat is unsaturated with monounsaturated fat being the single largest fat in egg (and egg yolk). The protein is digested in the stomach – broken down into amino acids. I’ve not yet seen any suggestion that protein clogs up arteries so let’s focus on the fat. (Plus – if the Canadians do come back and suggest that the protein element of egg yolks is an issue then we can talk about egg whites.)
The fat passes from our mouth very quickly into the pharynx (the part of the throat that goes from behind the nose to the start of the oesophagus) and then into the oesophagus (the muscular tube through which food travels from the mouth to the stomach). From there it goes into the stomach (the main area for food ‘short-term’ storage and digestion of protein and carbohydrate). Fat is not digested until it passes from the stomach into the small intestine (where almost all nutrients are absorbed) and, from there, it passes into the large intestine (the main function of which is to transport waste out of the body and to absorb water from the waste before it leaves). So, our egg yolk fat has quite a journey through our digestive system and we haven’t yet started to describe how it can go anywhere near our arteries.
Chylomicrons (the largest lipoproteins) are formed in the intestine, as a result of digestion, and chylomicrons are the transport mechanism for taking dietary fat (and cholesterol) from the digestive system into the blood stream and from there to the different parts of the body to do their vital work. As any young biology student will know, arteries pump blood around the body from the heart. There is no artery to take dietary fat away from the intestines.
The chain length of fatty acids determines how they are transported out of the digestive system. If a fatty acid has fewer than 12 carbon atoms, it will “probably travel through the portal vein that connects directly to the liver. If the fatty acid is a more typical long-chain variety, it must be reformed into a triglyceride and enter circulation via the lymphatic system.”[i]
The composition (by weight) of the most prevalent fatty acids in egg yolk is typically as follows:[ii]
Unsaturated fatty acids: Oleic acid, 47% (18 carbon atoms); Linoleic acid, 16% (18 carbon atoms); Palmitoleic acid, 5% (16 carbon atoms); Linolenic acid, 2% (18 carbon atoms) and
Saturated fatty acids: Palmitic acid, 23% (16 carbon atoms); Stearic acid, 4% (18 carbon atoms); Myristic acid, 1% (14 carbon atoms)
Egg yolks thus have no short chain fatty acids that may even head off in the portal vein to the liver (not that this should cause concern anyway). The longer chain fats (saturated and unsaturated) are packaged into chylomicrons, released into the lymphatic system and they glide from there into the blood stream to carry the vital nutrients around the body to do their vital work.
So, assuming that egg yolks have not been injected into our arteries, egg yolks have not gone into any arteries through any less invasive route. Egg yolks have gone on a normal digestive process journey, probably taking a few hours for fat, still without going into an artery. Yet, the world is now led to believe, thanks to the imagination of some Canadians, that eating egg yolks is going to clog up our arteries. I’d love to hear the process by which the authors think that the post digestion component parts of egg yolks leap out of chylomicrons, find their way into an artery and lay themselves down in the name of plaque. Or maybe they do inject egg yolks in Canada?!
[i] Gordon Wardlaw, Anne Smith, Contemporary Nutrition, seventh edition, McGraw Hill (2009).
[ii] ] (National Research Council, 1976, Fat Content and Composition of Animal Products, Printing and Publishing Office, National Academy of Science, Washington, D.C., ISBN 0-309-02440-4; p. 203)
65 thoughts on “Egg yolk consumption, carotid plaque & bad science”
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Let’s not take the risk that we’ll regret later on! If everybody would be wise enough to just eat a couple of eggs a week it would be the smartest and wisest choice as far as health and dietary choices are concerned. Aside from making that wise choice everyone should be on the move – that is, regular exercise, healthy diet, cut down altogether with smoking, moderate alcohol consumption (but abstinence for those who never drank alcohol) and regular health consultation with the doctor.
They actually adjusted for age in 2 ways.
First, they did not use egg-yolk years here, as age is obviously associated with that on top of being associated with TPA. Instead, they split the sample into 2 categories, 2 or fewer eggs/week and 3 or more eggs/week. So this really has nothing to do with any of the problems associated with using the variable “egg-yolk years”.
Then they also adjusted for the correlation of age and TPA.
The difference they found was still statistically significant.
I’m defending the article only as much as it deserves to be defended. the study adjusted for age and still found statistical significance. I just didn’t like how this review avoids acknowledging this.
What I think would be a better way to shed light on the meaning of this study is to look at the clinical significance of the results. The difference between the age adjusted findings is only approximately 6% increase in mean TPA, and one standard deviation is over 100% of the mean… The reason why this is the case is hard to determine based on the lack of control for diet and exercise in the study
your right it was inelegant. But remember they are researchers not writers.
Thanks for pointing out that.
However, I urge you to reread the study; they claim it is nonlinear but when I read it, I thought “this is built on pretty shaky sand”. If I remember correctly, the “nonlinearity” showed up as a dot in quintil 5 that was higher than “it should have been”. One dot. Then there was some issue with plaque linear to age only after a certain (age) offset, I believe. Meaning before that, you can accumulate “egg yolk years”, skewing things.
You are right that non-general population isn’t the researchers’ fault. I suppose they got this data as a side effect of their practice and should be lauded for not throwing it away. However, reading the study, my impression was that it was evaluated and presented in pretty inelegant ways. Quintiles etc. just invite artefacts.
This review is as bad as the article.
The study acknowledges that it is an association and not a causation between the variables. They also found a strong correlation between egg-yolk years and TPA after adjusting for the linear relationship between age and TPA, so the issue of age as a confounding variable has already been dealt with. This review fails to mention that.
Also, as acknowledged by the authors, the study used a sample of already at risk patients and never tries to apply this to the general population, what the newspapers write has nothing to do with the Canadian researchers.
A study does not need to explain a possible mechanism, it can be exploratory. They concluded that their hypothesis should be tested in a prospective study which would deal with confounders, allowing them to work towards a possible mechanism if the results call for one.
It was by no means a perfect study, but this review doesn’t tell the whole story.
I have been having Three rashers of Bacon and Two Eggs, cooked in a small amount of butter, each morning since last November. My Cholestrol has come down from 5.98 to last weeks check of 3.57. My case rests
If you use eggs that have been lain by hens fed on an “Industrial Diet”, That don`t have the same nutrient composition as their free roaming cousins then it is i think possible there is a modicum of truth in the story.
The same applies with Meat that has been reared on an ” Industrial Diet” as opposed to those raised on grass pasture.
For most, a trip to the local SuperMarket is as near as they get to knowing anything about the animal / Vegetable or its existence. Wben in the 21st century you still read about X% of children that dont know Fish Fingers arnt a real fish or Chicken Nuggets dont come from anywhere near a farm, There has been a successful disjoint between real and perception, Well done Admen !
If you buy the value range of whatever Product the chances are this story will have some meaning………. The dialemna is that many cant afford to do otherwise due to Budgetary constraints.
Excellent article and response. Why have they decided to continue giving egg yolks a bad name? Why not sugar and grains – the foods that actually do cause people a lot of health problems.
This makes more sense to me:
ASSOCIATION BETWEEN EXCESSIVE SOFT DRINK CONSUMPTION, NON ALCOHOLIC FATTY LIVER DISEASE (NAFLD), AND CORONARY ARTERY DISEASE
F. Nassar1*, A. Djibre2, A. Marmor3, N. Assy2,4
1Internal Medicine, Western Galilee Hospital, Naharyia, 2Liver Unit, 3Cardiology, Ziv Medical Centre, Safed, 4Faculty of Medicine, Technion Institute, Haifa, Israel. *[email protected]
Background/aims: Excessive soft drink consumption is linked with fatty liver. Fatty liver is increasingly associated with metabolic syndrome. However, the independent role of soft drink in Coronary artery diseases (CAD) remains unclear. The aim of the present study is to evaluate the relationship between soft drink consumption and coronary plaques in patients´ w/without metabolic syndrome.
Methods: 120 patients with low risk for CAD (Framingham score 50%. We measured degree of fatty infiltration by liver minus spleen density >/= -10(CT), coronary plaques and stenosis by cardiac CT, Intimae-Media thickness (IMT) of carotid artery by Doppler ultrasound and biomarkers of insulin resistance, inflammation, and oxidant-antioxidant status. Excessive soft drink consumption was defined as >50 g/day (>500cc/day; or>12 tsp/day) of added sugar.
Results: Patients with excessive soft drink beverage showed higher prevalence of coronary plaques (70% vs. 30%, P< 0.001), higher prevalence of coronary stenosis (30% vs. 10%, P< 0.008), Higher prevalence of severe fatty liver (71%, P< 0.001), Higher IMT (0.98±0.3 Vs 0.83± 0.1,P< 0.04), higher HOMA (3.8±3.6 vs. 2.6±3.2, P< 0.005), and higher triglyceride levels (208± 87 vs. 148±70, P< 0.005) than controls. Multiple logistic regression analysis showed that excessive soft drink (OR 2.5,95% CI 1-5, P< 0.01) beverage and fatty liver (OR 3, 95% CI 1-4,P< 0.001) are strong predictor of coronary and carotid atherosclerosis independently by metabolic syndrome or other biomarkers.
Conclusions: Patients with excessive soft drink beverage have higher prevalence of coronary and carotid atherosclerotic disease. The mechanism may be via fatty liver. This might help to optimize the cardiovascular risk stratification.
I’m not so sure there’s an easy correlation with blue socks–but I’m pretty sure that having people retroactively recall their sock habits and rolling it onto “blue-sock-years” might make it easier!
Being Canadian, I can confirm we indeed DO NOT inject our yolks. We do however eat them with fried potatoes, processed (with salt and sugar) meats, and oversized portions of toast slathered with sugary spreads.
I ant to add that as a Canadian I didn’t feel any offence to the “Canadian Author” comments. However, as an avid blue sock wearer I don’t apreciate them being maligned.
Oh boy – now the liberal Chicago Tribune is saying egg yolks are as bad as smoking… please make it stop!!
I still can’t get over David Spence’s last line:
“Stopping egg yolks after the heart attack would be like quitting smoking after the lung cancer is diagnosed.”
Dr. Spence has clearly made up his mind, so no reasoning or logic will work.
Hi Dr. Spence,
I agree with the fact that a post prandial increase in oxidized LDL contributes to atherosclerosis. However just having insulin resistance will increase LDL oxidation. High carbohydrate diets and low training status/sedentary behavior will increase ldl oxidation.
Fruits/veggies/antioxidants in general will decrease LDL oxidation. Heck I have even read it depends on what the hen was eating in terms of eggs causing ldl oxidation. http://pubs.acs.org/doi/abs/10.1021/jf073549r
So I guess my point is that given the evidence, couldn’t we expect an insulin sensitive person could eat whole eggs (laid by healthy hens) along with a low carb high antioxidant meal (berries and spinach.. or whatever) and not have any issues?
How about we set up a randomized control trial to prove it? If I win the lottery I am going to do it :)
Really I just want to know what is true and nothing seems to prove anything one way or the other it seems to me at least. I am a physician who uses diet and exercise to help my patients decrease their chronic diseases so I would love to know for sure what the heck the truth is.
I have found that many of my patients have been able to use whole eggs (plus egg whites) in conjunction with a low carb high antioxidant diet to decrease their weight/abdominal circumference, insulin resistance, and calculated CVD risk. Either way thanks for sharing your thoughts. Meanwhile I am buying a lottery ticket. :)
He seems so set against “the egg industry propaganda”.
I’ll just post these up for those that want to check to see if the egg industry funded them.
http://www.ncbi.nlm.nih.gov/pubmed/20071648 yes, this one is on sat fat
I’d also suggest the good doc read “Good Calories, Bad Calories” before talking on the subject any further.
Anyone with a bit of common sense would never set out to try and prove a REAL food is detrimental to health, for the masses. I add that last part so someone doesn’t chime in with “well, I’m allergic to peanuts and they could kill me.”
Seriously, how naive our humans to think that food, real food would ever be the cause of ill health… Dr. Price pretty much proved anything that needed to be proved with nutrition decades ago.
How anyone, can try and argue some of this is beyond me. Take your phoney science that scares people away from real food and onto fake processed health foods while they have diabetes and shove it. Seriously, I’m fed up.
I’m fed up trying to explain to obese people, or diabetics that perhaps their Cheerios may just not be better than eggs.
The full study is publicly available online — search via the journal that published the study.
Dr. Spence, thank you for your detailed followup reply. You have gathered some meaningful information for an at-risk segment of the population, and I hope that this at-risk group can benefit from your study.
However, a critical shortcoming of this study that I see is that the conclusions are being applied essentially to the whole population, and there really is no basis for this in the published study. This is partly a consequence of hasty mass-media reporting, but I would respectfully suggest that you might have offered some better responses to journalist’s inquiries to focus the message on the proper target audience.
I have ample evidence applicable to my own case that I feel quite comfortable in keeping eggs as part of my regular diet.
Many thanks for taking the time to reiterate your position in the article.
1) The animals first used to start this hypothesis were rabbits (Anitschkow 1913). Rabbits are herbivores. They do not eat animal foods, which is the only place where dietary cholesterol is found, so it’s not surprising that the poor bunnies clogged up! The same was found with chickens, leading Ancel Keys to say “There’s no connection whatsoever between cholesterol in food and cholesterol in blood. And we’ve known that all along. Cholesterol in the diet doesn’t matter at all unless you happen to be a chicken or a rabbit.”
2) Any allegation that dietary cholesterol increases the risk of heart disease (2 references) will be the usual bad science of: association not causation; relative risk not absolute risk and no other factors isolated. I really, sincerely would be able to find an association between colour of socks worn and heart disease and it would still be nonsense.
3) You still haven’t offered a plausible mechanism for how an egg (yolk alone) is supposed to get into the arteries to inflame them. You would have us believe that the people with the highest egg yolk consumption (still only 4.68 per week) have lower LDL cholesterol (and lower total cholesterol) than those with the lowest egg yolk consumption (0.41 per week) throughout your experiment when blood tests are being taken but in between, when they eat the egg yolks, LDL is up to all kinds of naughty stuff. The same LDL that is the carrier of cholesterol, protein, phospholipids and triglyceride to repair any damaged arteries.
4) You continue to assume that the evil part of the egg is the yolk because you have decided that cholesterol is bad. You recommend egg whites without explaining how you isolated egg yolk from egg white consumption. As I said in my blog – did all the egg eaters throw the white away? How do you know that the white does no harm?!
5) Eggs are mostly unsaturated fat so I’m not sure what the demonisation of saturated fat that slipped in was all about. It is impossible to consume the essential fats that we need to survive without consuming all three dietary fats – every food that contains fats contains all three fats – no exceptions.
6) You quote one study to damn saturated fat. I could quote many doing the opposite and we would be stuck in a long game. I’ll quote one – a 2010 meta-analysis of 347,747 people over a 5-23 year period concluded:
“A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD. More data are needed to elucidate whether CVD risks are likely to be influenced by the specific nutrients used to replace saturated fat.” (Siri-Tarino PW, Sun Q, Hu FB and Krauss RM, “Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease”, American Journal of Clinical Nutrition, (March 2010).)
The last sentence is key – the more we demonise real foods, like eggs, meat and so on, the more people turn to cereals and grains. This long study very sensibly says we need to question what we have put in our diets in place of these real foods that we have demonised – because we managed to get two thirds of our people fat and sick in the three decades that followed the idea that saturated fat was bad.
7) Tom Naughton did a great job of your diabetes/egg connection (http://www.fathead-movie.com/index.php/2010/11/04/more-bad-science-thats-eggsactly-what-it-is/) Diabetics who eat an egg a day were associated with more heart disease. Surely the ‘but for’ is the diabetes – a condition of inability to cope with glucose, not egg yolks. Were the egg eaters dipping soldiers in them?! (as we call them in the UK)
8) Regarding the conflict, you’ll have to forgive me if I think that someone who receives funding from companies that profit to the tune of billions of dollars by blocking the human mevalonate pathway may not be prioritizing human interests and health.
Best wishes – Zoe
Dr. Spence — Thanks for your reply to this thread! A couple of questions:
1. What were the controls in your study?
2. Assuming BMI is body mass index, wasn’t the average pretty high? Since anything over 25 is generally considered overweight, couldn’t that have been an problem, too?
There are so many misconceptions in the story and responses that it is hard to know where to begin.
It has been well known for many years that dietary cholesterol causes atherosclerosis in animal models 1,2, and increases the risk of human cardiovascular disease3,4, but this truth has been obscured in recent years by the remarkably successful propaganda of the egg marketers5. Diet is not about fasting LDL cholesterol; it is about the post-prandial state6. For several hours after a high-cholesterol meal or egg yolk consumption, there is inflammation in the arteries, increased oxidative stress, an increase of oxidized LDL cholesterol by almost 40%, and impairment of endothelial function5. Dietary cholesterol is permissive of the harmful effects of saturated fat. 5
The mantra of the egg marketers, that “eggs can be part of a healthy diet for healthy people” is a half-truth, based on the first part of the story from two US studies that showed no harm from eggs among people who remained healthy during followup7,8. The other half of the story, that you never hear from the egg marketers, is that in both those studies, an egg a day doubled coronary risk among those who became diabetic during followup. In the US Health Professionals study the followup was only 8 years in men and 14 years in women, and the mean age was early 50’s in the men and mid-40’s in the women, so the followup was probably not long enough to show harm among those who remained healthy. Diabetics are at higher risk, so it was easier to show harm in them. A Greek study in diabetics9 showed that an egg a day increased coronary risk 5-fold; perhaps the healthier Greek diet made it easier to show harm from regular intake of egg yolks.
With regard to the question of conflict of interest, there is none. I spend more time with my high-risk vascular patients on diet than on prescribing drugs, because diet is more important. Drugs are not an alternative to diet; they are complementary. Diet accounts for as much as 85% of coronary risk10. Indeed, among patients who had survived a heart attack, the Cretan Mediterranean diet11 reduced coronary risk by more than twice as much (70% in under 3 years) as did simvastatin in the contemporaneous 4S trial12 (40% in 6 years). What patients can do for themselves is more important than what their doctor can do for them; this is the reason I wrote my book for the public, “How to prevent your stroke”.13
Egg whites are a good source of protein, and there are safer ways to obtain the other nutrients in the yolk. A tasty omelette or frittata made with egg whites, or with egg-based substitutes such as Egg Beaters, Egg Creations, Better ‘n Eggs, etc., is a good alternative to a meat-based meal. Carotid plaque, which is a strong predictor of the risk of heart attacks and strokes, goes up linearly with age, but accelerates with both smoking and egg yolk consumption. If you are 20 years old, you might think you can eat egg yolks with impunity because your heart attack or stroke is 45 years or so in the future – but why would you want to make your arteries worse in the meantime, and bring it on sooner? Stopping egg yolks after the heart attack would be like quitting smoking after the lung cancer is diagnosed.
(1) ANDRUS SB, MANN GV. Xanthomatosis and atherosclerosis produced by diet in an adult rhesus monkey. J Lab Clin Med 1956 October;48(4):533-50.
(2) GRESHAM GA, LEAT WM, HOWARD AN, JENNINGS IW. PATHOLOGICAL CHANGES IN PIGS REARED ON SEMI-SYNTHETIC DIETS CONTAINING NO FAT, BEEF TALLOW AND MAIZE OIL. Br J Exp Pathol 1964 April;45:128-34.
(3) Kushi LH, Lew RA, Stare FJ, Ellison CR, el LM, Bourke G et al. Diet and 20-year mortality from coronary heart disease. The Ireland-Boston Diet-Heart Study. N Engl J Med 1985 March 28;312(13):811-8.
(4) Shekelle RB, Shryock AM, Paul O, Lepper M, Stamler J, Liu S et al. Diet, serum cholesterol, and death from coronary heart disease. The Western Electric study. N Engl J Med 1981 January 8;304(2):65-70.
(5) Spence JD, Jenkins DJ, Davignon J. Dietary cholesterol and egg yolks: Not for patients at risk of vascular disease. Can J Cardiol 2010 November;26(9):e336-e339.
(6) Spence JD. Fasting lipids: the carrot in the snowman. Can J Cardiol 2003;19:890-2.
(7) Hu FB, Stampfer MJ, Rimm EB, Manson JE, Ascherio A, Colditz GA et al. A prospective study of egg consumption and risk of cardiovascular disease in men and women. JAMA 1999 April 21;281(15):1387-94.
(8) Qureshi AI, Suri FK, Ahmed S, Nasar A, Divani AA, Kirmani JF. Regular egg consumption does not increase the risk of stroke and cardiovascular diseases. Med Sci Monit 2007 January;13(1):CR1-CR8.
(9) Trichopoulou A, Psaltopoulou T, Orfanos P, Trichopoulos D. Diet and physical activity in relation to overall mortality amongst adult diabetics in a general population cohort. J Intern Med 2006 June;259(6):583-91.
(10) Hu FB, Stampfer MJ, Manson JE, Rimm E, Colditz GA, Rosner BA et al. Dietary Fat Intake and the Risk of Coronary Heart Disease in Women. N Engl J Med 1997;337:1491-9.
(11) Renaud S, de Lorgeril M, Delaye J, Guidollet J, Jacquard F, Mamelle N et al. Cretan Mediterranean diet for prevention of coronary heart disease. Am J Clin Nutr 1995 June;61(6 Suppl):1360S-7S.
(12) Scandinavian Simvastatin Survival Study Group. Randomized trial of cholesterol lowering in 4,444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S). Lancet 1994;344:1383-9.
(13) Spence JD. How to prevent your stroke. Nashville: Vanderbilt University Press; 2006.
i foresee hundreds of thousands of people dying from second hand yolk.
Thank you so much for this great explanation of the numerous weaknesses in the Spencer et al study. In the early ’70s, I worked for a biochemistry professor in nutritional science at Cornell whose obsession was to prove dietary cholesterol led to atherosclerosis. He expended lots of tax dollars (via NIH grants) on research that involved feeding cholesterol to rats and bunnies. I never found his results convincing and was happy to see the hypothesis soundly debunked a few years later. Imagine my dismay upon reading about the Canadian study on a CNN blog yesterday. Then I read your excellent and thorough rebuttal this morning. Yea! I especially appreciate your comment that “plaque itself is not the root cause of problems.” This seems to be a failing common to many nutritional studies, i.e., not focusing on root causes. Keep up the good work!
I agree that the difference in age across the study groups is a limitation of the study, and it is interesting that the HDL and LDL profiles are “best” in the group with the highest yolk-years. (The quotations are necessary, of course, due to our ever-changing understanding of these lipoproteins.)
However, I am curious why you list all the vitamins and minerals present in the egg white v. yolk, but you don’t list their relative cholesterol content. Namely, the egg white has essentially no cholesterol in it, while the yolk has ~1gram.
Cholesterol is an important part of plaque formation, and whether an individual agrees with the authors’ findings, if you are going to show the nutritional content of the egg’s constituent parts, why not list the relevant nutrients implicated in the paper?
Hi Michael – I don’t list cholesterol in eggs because it’s irrelevant.
1) Keys spent the early part of the 1950’s trying to prove that cholesterol in food impacted blood cholesterol levels and concluded unequivocally that it did not. (Ancel Keys, J. T. Anderson, Olaf Mickelsen, Sadye F. Adelson and Flaminio Fidanza, “Diet and Serum Cholesterol in Man: Lack of Effect of Dietary Cholesterol”, The Journal of Nutrition, (1955).) He never deviated from this view.
2) The authors have exonerated blood cholesterol as an issue in their study as they have shown that people eating an average 4.68 egg yolks per week have lower total cholesterol, lower triglycerides, higher HDL and lower LDL than people eating an average of 0.41 egg yolks per week.
Add to these two the – what plausible mechanism is there? and I still don’t know how the digested component parts of egg yolks are supposed to leap out of chylomicrons and form plaque in arteries.
Best wishes – Zoe
Zoe: Great post. My husband, daughter, and I each eat about 3 eggs per day. My husband just heard a media mention of this study today and was distressed by the bad news on egg yolks. I was happy to tell him it was bunk and read your post (for the second time) to him. As an American I took no offense to the reference to Canadians — actually, having formerly lived in Minnesota where it was required to make Canadian jokes, the end was very funny (let’s lighten up people). (And I too, will be sure to get rid of my blue socks). Thanks for your website!
What I don’t understand is the conflict of interest. If I wanted to peddle statins, I’d want people to eat MORE eggs, and this study would have the opposite effect.
Good post Zoe!
Hi Zoe, thanks for taking the time poke and prod this article and keep this type of work in context for readers. Should your readers be interested in “double-clicking” on the role between dietary cholesterol (i.e., the cholesterol in eggs), plasma cholesterol (i.e., what doctors measure), and arterial wall cholesterol (i.e., the one thing we’re trying to mitigate), they might find interest in my series on cholesterol, The Straight Dope on Cholesterol. It’s a 9 part series and growing, including a summary piece I’ll write for Mark’s Daily Apple next week. Here’s part I, which fits in nicely with your analysis:
Hi Peter – many thanks for this. I’ve seen your series – great reading!
Best wishes – Zoe
p.s. one bit I don’t like is the link to the Daniel Steinberg book from concept 5. Steinberg is the devil incarnate to people appalled at the multi billion dollar industry that has been created by drug companies in the name of lowering one of the most vital substances in the body – cholesterol. The Yoseph book “How statin drugs really lower cholesterol and kill you one cell at a time” would be a better historical book to link to! The story from a non conflicted point of view :-)
Did you really need to make those snide, immature comments about Canadians at the end there? There is questionable science going on all over the world, and it doesn’t help your critique to belittle others based on their nationality. Unimpressed.
euh… your table showed egg yolk contains more vitamins and minerals than a whole egg. How could it be?
Ken – simple – 100g of egg yolk is more nutritious than 100g of whole egg because the whole egg is dragged down by the not-so-nutritious egg white. Table says “All per 100g of product”
Best wishes – Zoe
Great article! The data appears to suggest a linear correlation of simple age and smoking with plaque build-up. (E.g. the category C participants consumed six times as many eggs as category A, but only had a 12% increase in plaque area… they also smoked 15% more.)
As a Canadian, the study and your references to “the Canadian researchers” made me cringe. No we don’t inject our eggs up here, but I do eat nearly a dozen a week, and this “study” sure won’t make me stop.
Eating omega 3 leads to omega 3 in your brain, so there must be some dietary to blood link??? I think this article is non scientific… who knows the answer to this long standing debate but I am going to be on the safe side and cut down on egg yolks.
Not all eggs created equal.
Some are organic, grass feed, caged, caged free. They all have different nutrient values.
If you have chickens or hens which lay eggs for you, that’s the healthiest ones ever! If you bought it from the store, never know where the eggs come from and the eggs have been aged for some times, maybe 2 to 3 months of time before go on Grocery shelves.
I usually buy eggs from my friends because she has hens at home, and it’s all organic and natural.
I agree with Paul, the anti-Canadian prejudice here was uncalled-for and irrelevant to your points about the authors’ bad science and faulty conclusions.
Dear all taking offense at the reference to the Canadian authors – I didn’t mean to cause any offense and I’m very sorry if you feel offended. I’m disappointed in the people involved in this study and if that excludes you that excludes you! Using the term Canadian authors is just a way of referring to the group. I could put David Spence, David Jenkins and Jean Davignon all the way through and it would get a bit laborious. I do the same on other blogs about studies. It’s usually Harvard coming out with nonsense so I refer to Harvard guys or the Scandanavian authors (in another recent very bad study).
I say Canadian authors and Canadian guys so you should know the three I’m talking about. The last comment was meant to be funny and to show how ludicrous the idea is that eggs can get into arteries. Please be upset at the people who are funded by drug companies and demonise real food, to the benefit of fake food, not an independent blogger trying to defend nature’s provisions unfunded!
Best wishes – Zoe
Thank you for the meta-analysis. As usual, ‘experts’ make broad, sweeping statements about human diet and health, with very limited data. The media gobble it up and daytime talk shows start airing segments.
This 3-4 daily egg consumer will wait for a scientist (whom is not supported by big pharma) provides compelling correlation before changing habits.
FYI, at tidbit you didn’t mention: “The study looked at data from 1,231 men and women, with a mean age of 61.5, who were patients attending vascular prevention clinics at London Health Sciences Centre’s University Hospital.”
The sample set was FAR from random; patients at vascular prevention clinics?
An excellent description of how everything eggy works – many thanks for taking the time and reassure those of us who, like me, eat loads of the things.
Good thing that you pointed out they were Canadian so many times…
What a stupid point to be constantly bringing up…
I live in London, Ontario – home of UWO and this “study”. I have to say that I’m totally embarassed by it – and the correlation with Canadians!
I’m not funded by a drug company. I follow the primal blueprint and I eat at least two eggs EVERY SINGLE DAY. We’ll see if I drop dead at an early age or if I live to be 93 like my grand parents.
Well said Zoë. Why do peer review journals continue to publish such rubbish, even when the authors even admit to the limitations of this study? Observational studies can be useful, but only when there are STRONG associations observed, not the case here – Denver’s diet doctor
I dont think that that was a standard deviation. I think that might be the range.
Agree with RedShox….the standard deviation is greater than the actual measurement itself, which means the results were not very “tight.” Honestly, I’m surprised this even got published in a peer-reviewed article.
Also, one of my favorite sayings, “Correlation is being confused with causation” applies here! There might be a relationship to egg yolk and plaque, but this study does not prove that egg yolks caused it. For all we know, the people surveyed could be eating a block of cheese and butter-soaked pancakes every day. :)
This statement blows my mind:
“Plaque area in patients consuming <2 eggs per week (n = 388) was 125 ± 129 mm2, versus 132 ± 142 mm2 in those consuming 3 or more eggs per week (n = 603); (p < 0.0001 after adjustment for age)."
The idea that they can get a p-value that low with two essentially overlapping distributions (look at the standard deviations!) is ridiculous.
Peter Attia explains the relationship between dietary cholesterol and serum cholesterol on his blog, The Eating Academy… It is actually an incredibly thoughtful series of posts that explain what cholesterol is, why it is absolutely necessary for our survival, how cholesterol actually be measured to be of any value in determining risk for heart disease, etc.
More over, you’re little biology lesson at the end didn’t really explain anything. For example… what happens when there is an excess of the long or fat chains of fats?
The strongest relationship isn’t between age and plaque area… it’s between their so-called yolk-years and plaque area… not sure if you passed stats…
Also, feel free to mention to everyone here why you’re writing this critism in an online blog? Profit right? If you’d like to refute this article properly, you should re-read the methods and perform this experiment.. then any educated person can and will take you seriously (Scientific Method,.. do you remember your first year in undergrad biology?)
Last note, the people that read this and find it ‘useful’ in any way, need to start thinking for themselves! People think that online blogs are more credible than scientific experiments… really…
Just so you all know, I’m not convinced either… but I do not discredit scientists that have obviously worked hard and collected TONS of data (try doing data analysis on 1200 people?).
Taking a look at your analysis and will read the article myself once it becomes available from my library…
The only question i find here, is why they chose this “Yolk years” business… The Yolk years can only be used if the mean age of the sample was the same, which here it wasn’t.
I wouldn’t entirely discredit this article however… It does need some further study.
By the way. In any situation, there will be someone pushing for something and against. Egg producers will be against it and drug companies will be for it. That doesn’t mean that the data is skewed, Western (UWO) is regarded as one of the best schools in North America (in the top 5 in Canada for years)
I find these retro papers quite charming. Still, just to be sure, I am going to get rid of my blue socks.
The great Richard Feinman – I am truly honoured! Thankyou! ;-)
Did the blue sox vs. red sox adjust for age and presented gender?
You should send that description of fat processing to Dr. Oz,because,he actually thinks the glob of fat from a pork chop,gets into the blood stream wholly,and moves around the body until it gets stuck in the largest pipes.What is 49 in egg yolk years?
Do I have your permission to quote from this article,should I respond to this garbage if/when it shows up in my local paper? Thanks.
Hi Mike – please do! Best wishes – Zoe
Great analysis. Are these the fools who wrote about the “seventh egg” that R. D. Feinman derided?
They could have used broccoli or milk or anything as a control to give it more edge.
Reading this made me feel like eating an egg or three.
One thing that might well cause calcification of arteries is the statin drugs, which deplete vitamin K2, the calcium-shifting vitamin.
A brilliant and much-needed analysis of yet another shock-horror epidemiological study. It’s depressing that these poorly-controlled studies are used to directly influence public health messages when they are not designed to measure actual differences in health outcomes. Keep up the good work – I’ve tweeted this page to all my followers.
Diane, it makes perfect sense if you Follow the Money. ;)
Wow, I think i must be about to drop dead any second as I eat 2-4 eggs a day!!! I wonder how many egg-yolk years I have lived and how many I have left!!!!
It was established in the public domain only a short while ago that eating eggs doesn’t raise cholesterol and that it was safe to eat as many eggs as you want. Why are eggs under attack again? It makes no sense!