Still no good evidence that eggs cause heart disease (despite what some may say)

Eggs are one food that have had wildly different press from the nutritional community over the years. Back in the 1950s, here in the UK, we were encouraged to ‘go to work on an egg

All that changed, though, when we got all cholesterol-conscious and fat-phobic back in the 70s and 80s. Recently, there was a chance of eggs being rehabilitated, mainly on the basis that egg eating did little to raise cholesterol levels, so was unlikely to raise heart disease risk. But this week saw the publication of a study which give a damning verdict on eggs [1]. Three doctors based in Canada warn, in this review, that “patients at risk of cardiovascular disease should limit their intake of cholesterol,” and that “Stopping the consumption of eggs yolks after a stroke or myocardial infarction [heart attack] would be like quitting smoking after a diagnosis of lung cancer: a necessary action, but late.”

The review focuses on so of the biochemical changes induced by egg eating that might, in theory at least, cause cardiovascular disease. Cholesterol, inevitably, features heavily. The authors can’t quite bring themselves to be up front about the fact that egg eating does not raise cholesterol levels. The focus is shifted to things like cholesterol oxidation, raised fat levels in the blood after meals, and the idea that cholesterol “potentiates the adverse effects of dietary fat.”

Well, saturated fat doesn’t appear to have any adverse effects regarding cardiovascular disease risk, so that idea is essentially dead in the water. And so what if eating food with fat in it causes blood fat levels to go up? It’s what you’d expect. What is really important is the impact a food has on health and disease risk. ‘Surrogate markers’ such as blood fat levels are not to be relied upon to judge the impact of any factor on health. If arsenic or cyanide reduced cholesterol levels, would we recommend that everyone swigs back these poisons everyday?

To really judge the impact of eggs on health we require intervention studies. For example, we could take a group of individuals and instruct them to eat lots of eggs over a long period of time and then assess their health compared to a group eating fewer eggs. We don’t have such studies.

So, inevitably, scientists have turned to ‘epidemiological evidence’. This sort of evidence at best can tell us about relationships between things. It cannot prove that one thing causes another (or that one thing does not cause another, for that matter).

Anyway, the point is there have been some epidemiological studies that have found in healthy individuals, higher egg consumption is not associated with an enhanced risk of cardiovascular disease [2,3]. The authors are dismissive of this finding though, and suggest it’s most likely caused by the studies lacking the ‘statistical power’ to detect a link.

Interpretations of this type, in my mind anyway, smack of ‘bias’. It’s just the sort of comment authors who have made up their mind about what they want to find make. Is there any other evidence of bias in this review? You bet.

For a start, the authors are dismissive of these epidemiological studies ‘lacking statistical power’, but quote one of these studies as evidence of a link between egg eating and cardiovascular risk in diabetics (suggesting that the power here was sufficient).

They also do not pause to think about what might have led up to such a finding. It could be that individuals who are not very health conscious continue to eat relatively large amounts of eggs, and it’s not the eggs, but the laissez faire attitude about their health that explains this association. I wrote about this recently here.

The authors also quote a study which found that eggs eating was not linked with an increased risk of cardiovascular disease [4], but was associated with an increased risk of death. Now the authors spend a lot of time highlighting the supposed perils of eggs with regard to cardiovascular health. And then quote a study linking eggs are linked with an increased risk of death but not cardiovascular disease. So if it’s not cardiovascular disease that’s killing people, what is it? The authors don’t even suggest an explanation here, so let me do their job for them: the likely explanation is that egg eaters are, generally speaking, less health conscious (see above), and are at increased risk of dying as a result of other lifestyle factors associated with not being very health-conscious (such as being sedentary and smoking).

More evidence of bias in this review comes in the form of the language the authors sometimes use. Look at these two sentences:

“A recent re-analysis of the smaller Physician’s Helath Study…[showed] that regular egg consumption doubled all-cause mortality.”

“Two recent studies also showed that consumption of eggs increased new-onset diabetes, independent of other dietary factors.”

To read these sentences you’d think that the observations they refer to had been made via intervention studies that can discern cause and effect. But, in reality, they refer to epidemiological studies, the results of which we can be circumspect about at best. Essentially the authors of review have taken some quite weak evidence, and expressed in a way that suggests eggs cause diabetes and can kill.

Bias creeping into science is not a good thing, and it’s sometimes useful to ask where such bias may come from. Well, here’s the conflict of interest statement from this review:

“None of the authors receives funding from purveyors of margarine or eggs. 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.”

Seems like two of the authors of this review have some potential interest in keeping the cholesterol theory alive and well.

Look, we simply don’t have definitive evidence which tells us whether eggs are healthy or not. But in the presence of evidence which does not incriminate them, as well the weak and inconsistent nature of evidence used to damn them, I’ll continue to ‘take my chances’ with this natural and nutritious food.

References:

1. JD Spence, DJ Jenkins, J Davignon. Dietary cholesterol and egg yolks: Not for patients at risk of vascular disease. Canadian Journal of Cardiology, 2010; 26 (9): e336-e339

2. Hu FB, et al. A prospective study of egg consumption and risk of cardiovascular disease in men and women. JAMA. 1999;281(15):1387-94.

3. Quereshi AI, et al. Regular egg consumption does not increase the risk of stroke and cardiovascular diseases. Med Sci Monit. 2007;13(1):CR1-8.

4. Djousse L, et al. Egg consumption in relation to cardiovascular disease and mortality: the Physicians’ Health Study. Am J Clin Nutr 2008;87(4):964-9.

24 Responses to Still no good evidence that eggs cause heart disease (despite what some may say)

  1. Jamie 5 November 2010 at 2:52 am #

    Great review John! I saw the initial alert to this review and just cringed.

    Let’s take an English (and NZ) favourite – sausages, eggs, and chips. Now if we see an increased risk in CVD in individuals who eat this sort of meal (as you might measure in an epidemiological study), what is the cause? Is it the eggs? The fat? Or could it be the chips? Or even the ingredients in the sausages?

    No, you are right, it would have to be those cholesterol-laden eggs.

  2. Lynda 5 November 2010 at 11:10 am #

    Perhaps the so called studies have forgotten that eggs are a good source of protein and eaten in moderation are beneficial. I follow the GL diet, and am a vegetarian and include at least 4-6 eggs per week in my diet (free range of course).
    Its about time these so called studies on food that state they are “dangerous” for our health looked at other factors before making such rash statements.

  3. helen 5 November 2010 at 11:11 am #

    lets just blame a food that can actually keep you healthy forget that we have eaten eggs since the chicken was invented – just like the idiotic tv report that was on this morning entitled ‘can vitamin suppliments actually cause you harm?’ as one of my favourite doctors says ” and Jesus wept!” what more evidence to we need that the drug companies want us sick and dependent on their major killers drugs.

  4. Hans Keer 5 November 2010 at 11:15 am #

    “Eggs eating was associated with an increased risk of death”. This can have something to do with the leakiness of the gut caused by egg white http://bit.ly/a9Gvjk.

  5. Justmeint 5 November 2010 at 11:41 am #

    Because cholesterol is a major component in all animals’ bodies, eggs have a very high cholesterol content. That is why we are still told to eat no more than about 3 a week. Dr Uffe Ravnskov did his own test of this theory by eating a total of 59 eggs over 9 days. Did his cholesterol level shoot up? No, it fell by more than 11% from 7.23 mmol/L to 6.39 mmol/L.[5]

    http://www.second-opinions.co.uk/chd-2.html

  6. Michael Sweeney 5 November 2010 at 12:26 pm #

    Very good article,more so that I have just had my daily egg for breakfast.
    The ‘cholesterol industry’ takes another stiff jab from Dr Briffa, keep up the good work.

  7. Robin 5 November 2010 at 2:03 pm #

    Prof Uffe Ravnskov conducted an experiment on himself where, if I remember correctly, he eat about 60 eggs in a week. His cholesterol levels fell.

  8. Megan 5 November 2010 at 5:24 pm #

    I imagine that eggs were the most available, least combative source of protein for early humans and that we are perfectly adapted to them. Despite a diet high in fats and protein from eggs, fish and meat, my cholesterol remains very low. How many more statins will be dispensed before it’s accepted they do more harm than good?

  9. Pasi 5 November 2010 at 5:50 pm #

    Interesting from the China Study about egg, analyzed by Denise Minger:

    NEGATIVE CORRELATIONS (more eggs = fewer of these diseases)

    Liver cirrhosis: -46***
    Peptic ulcer: -43**
    Diseases of the blood and blood-forming organs: -35*
    Death from all causes: -33*
    Digestive disease other than peptic ulcer: -30*
    Hypertensive heart disease: -28
    Oesophageal cancer: -26*
    Death from all non-cancer causes: -26

    ref http://rawfoodsos.com/2010/06/18/a-closer-look-at-the-china-study-eggs-and-diseas/

  10. Jill H 5 November 2010 at 9:54 pm #

    I agree with Jamie – excellent review Dr B. I shop in a co-operative that lists whether the eggs on the shelves are from hens that have been pastured – allowed to live a life normal to a chicken instead of being turned into an industrial laying machine and a young man saw me picking eggs at twice the cost of other eggs on the shelf and asked me why? My husband walked away knowing what was coming. But I tried to explain the best I could that a diet of grass for most of our food animals means a good balance of health giving fats (more omega 3s, less omega 6s etc) and higher levels of vitamins and that if he took the more expensive eggs he would see a wonderful bright orange color to the yolks – beta-carotene, and that although from the outside an industrial egg looks exactly like a pastured egg and although, yes, the pastured egg does cost more – they could be considered two different foods in my opinion. He thanked me and gave me a coupon he had collected to get a discount at the checkout. I should imagine, as Megan has said, that most people are well adapted to eat them inasmuch as from the dawn of time all over the world eggs would probably have been collected from birds nests as a source of food and that eggs from pastured chickens are an important, relatively inexpensive, nourishing food for many of us.

  11. Heather B 6 November 2010 at 11:21 am #

    I eat an average of 4-5 free range eggs per day. I have a 3-egg omelette for breakfast and most other foods I eat during the day have eggs as an ingredient as my way of eating is high protein.
    Whenever I have my annual health review (for insurance purposes)my cholesterol levels are well within normal bounds.Two weeks ago, I was told that I have the heart of a 25 year old – I am 64 years old. I don’t plan to change my “unhealthy” diet any time soon.

  12. Joanna 6 November 2010 at 7:38 pm #

    Thank you, John for taking the time to review so ably this piece of ‘research’. I shall continue enjoying my high-egg diet!

  13. Jake 6 November 2010 at 10:35 pm #

    I upped my egg consumption from 2 a week to 18 a week in an effort to loss weight.

    Yes, I these endured profound side effects:

    1. Lost 34 pounds. 3 egg breakfast keeps me full for 3 to 6 hours.

    2. My LDL went from 140 to 112, my sdLDL fell by 66% and my HDL went from 51 to 75. Eggs have been proven to improve your lipid profile especially when they replace cereal breakfasts.

    3. My vision vastly improved as eggs are a perfect vitamin package needed by your eyes. No macular degeneration for me.

    It is quaint to see there are still doctors who believe those old 20th Century nutrition myths.

  14. Bill 7 November 2010 at 12:17 am #

    I’d highly recommend this interview with Dr. John Ioannidis a Greek researcher who has shown most epidemiological health research is likely to be false. Far from being shunned by the medical research community they grimly accept his conclusions!

    http://www.theatlantic.com/magazine/archive/2010/11/lies-damned-lies-and-medical-science/8269/

  15. enid Shaw 7 November 2010 at 6:14 pm #

    I thought that eating the whole egg counteracts the cholesteral.

  16. Neville Wilson MD.,MSc 7 November 2010 at 8:47 pm #

    In 2007 I conducted a personal experiment by eating 5 to 7 eggs a day and checking my lipid profile on a daily basis for 10 days. My lipid profile remained normal,with minimal change from baseline and a reduced total cholesterol over the 10 day period.I did not continue the experiment as I had no natural desire to consume more than 2 eggs per day.
    I eat 2 eggs every day and have a healthy total cholesterol/HDL ratio of between 4 and 5.
    The authors of the study are speculating and have no hard data to support their hypothesis.

  17. Rick 22 March 2011 at 1:13 am #

    “Physician’s Helath”
    Was this mistake in the original? If so, please add a “sic” to make that clear; if not, please correct it.

  18. Richard Feinman 22 March 2011 at 8:33 pm #

    Readers might be interested in my blog on dJousse (reference 4). http://rdfeinman.wordpress.com/
    title: The Seventh Egg.
    I think Dr. Briffa was too kind to these guys.

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