Do Eggs Cause Heart Disease?
It takes a lot to get me to react to any health headline. I'm used to them. I'm immune to the sensationalism, over-stated conclusions, and twisted information that comes with almost any new study abstract.
So I won't downplay my reaction when I read the following:
I thought it was a joke. Only I wasn't laughing. In fact, if you hear rumors that I was crying in my office, I won't deny them. After all, it's no secret that I'm one of the biggest supporters of eggs. If you're not aware, I did my own "eggsperiment" where I ate three eggs per day for two months just to see what would happen to my health. Type in "eggsperiment" and you'll find all my posts, but here was the conclusion. (Spoiler: My cholesterol improved and I even lost some fat.)
So if I was wrong--and I'm always open to that possibility--I was going to have to do a lot of damage control and follow up research.
But my bigger concern was that after 15 years of trying to debunk the "yolks are bad" myth, a new--potentially more dangerous and careless--conclusion could cause people to unnecessarily avoid one of the world's greatest health foods. (Note: If you're allergic to eggs, obviously they are not good for you.)
So I read the study. And found what I expected: Erroneous conclusions, a flawed methodology, and some questionable data.
Their reactions? Disbelief and frustration.
"The problem, unfortunately, is that this study has more holes in it than Swiss cheese," says Mohr. But he wasn't alone. "We shouldn’t look at research in a black box," says Roussell. "Just because a study is new doesn’t mean everything published before it was wrong. The data looking at the associations between egg consumption and coronary events is inconsistent at best."
But the issues with this research go deeper than just ignoring years of data that has suggested eggs are healthy. The flaws within this specific study include:
- The observational nature: Correlation does not necessarily mean causation, says Aragon. This is perhaps the biggest limitation of observational studies. There are uncontrolled variables that can render a suspect--in this case eggs--guilty by association rather than by their own actual effect. For example, they didn’t look at exercise, saturated fat or cholesterol intake (other than eggs), sugar or any other dietary intake, or waist circumference, adds Mohr. This is why observational designs can, at best provide food for thought but not cause for action, says Aragon. Studies such as this are mere starting points for further investigation. They can serve to generate hypotheses which can be tested in randomized controlled trials, where causation can be demonstrated.
- The Test Group: The people in this study were not healthy people, says Rousell. It's clearly stated in the methods of the study: “Our referrals were scheduled on an urgent basis soon after transient ischeamic attacks or strokes.” These were people with vascular disease. Making a generalization from the unhealthy to the healthy is dangerous and inaccurate. What's more, the way that the data was gathered makes it more susceptible to inaccuracies, says Aragon. Food frequency questionnaires (FFQs), although the most commonly used means of dietary data collection, are a necessary evil since they are inexpensive and convenient to administer.
- Lack of data on exercise: We already mentioned that exercise was not controlled for in the study. This is important because exercise is a well-established protective factor against atherosclerosis. And yet in this study, there was no measure to assess whether the participants were active. Missing data on formal exercise and physical activity can greatly weaken the possibility to draw firm conclusions about the outcomes of this study, says Aragon. "It’s highly unlikely that a moderate intake of eggs would significantly impact heart disease risk in physically active individuals with otherwise sound lifestyle and dietary habits."
- Questionable Data: "Individuals who ate the highest amount of egg yolks had the lowest total (and LDL) cholesterol levels. They also had the lowest BMI," says Aragon. "Are we to conclude from this data that lowering your BMI and cholesterol levels leads to arterial plaque build-up?"
Just think about that. These are indications of healthy people. So the link is questionable--at best. This is yet another example of how self-reported data within observational study designs is sometimes virtually worthless, says Aragon. Even the researchers admit this possibility, adds Roussell. Within the study, they state the following:
“The study weakness includes its observational nature, the lack of data on exercise, waist circumference and dietary intake of saturated fat and sources of cholesterol other than eggs, and the dependence on self-reporting of egg consumption and smoking history, common to many dietary studies."
- Lack of uniformity of data collection: Aragon discovered another very significant flaw: "The patient histories examined span back to 1995, and in the early years of data collection, smoking and egg consumption were recorded on a different lifestyle questionnaire compared to 2000 and onward, where data was collected on an urgent basis soon after patients had heart attacks or strokes." Lack of consistency in any study is a reason to have a lack of faith. This introduces further error on top of the error inherent with self-reported data.
- Lack of support from controlled research: "When there is consistent agreement between the outcomes of controlled research and observational research, it lends strength to any given claim about the relationship between any given dietary factor and its effect on health and/or disease," says Aragon. But this does not apply to eggs. "While observational studies have admittedly been a mixed-bag of outcomes, controlled studies on the effects of eggs have for the most part been neutral-to-positive."
As always, the foods you eat are your choice. If you don't want to consume a particular food, then don't. It's your life and your body and you should feel empowered to make the choices that are both sustainable and create a sense of dietary comfort. But for a scientific perspective, there's no reason to fear omelets, scrambles, or frittatas until controlled research can provide a cause-and-effect relationship between eggs and disease. If you suffer from vascular disease, it might be wise to watch your egg consumption, suggests Roussell. Otherwise, there's a lack of scientific support that should make you fear the incredible edible egg. Not to mention, eggs--and especially their yolks--are still loaded with valuable nutrients, protein, and healthy fat, says Mohr.
Still not convinced? I'm giving eggs my personal stamp of approval by heading straight to the kitchen to enjoy the Born scramble.
Want more from our experts? Leave them a question below or visit their sites:
Alan Aragon: http://alanaragon.com/
Mike Roussell: http://mikeroussell.com/
Chris Mohr: http://www.mohrresults.com/