Response to Eggs And Cigarettes Study

Eggs have been given a bad name. Recently a study compared eating eggs with the effects of smoking. The study was flawed, but the media ran with the dramatic statement. In the study researches went to the vascular clinic of Ontario’s Western University Hospital. They asked patients there a few questions, and then tallied results. They asked about how many eggs they eat, and about their smoking habits. This information was used to come to the conclusion that eggs cause plaque to build up in the arteries at 2/3 the rate of smoking. The problem with this is that many variables were not accounted for.

Let’s play a little game of fill in the blank. If I say _______ and eggs, what is the first word that you think of? The top answer is bacon, and ham is also popular. It is possible, perhaps even likely, that the people who reported eating more eggs also ate more processed meat. But we don’t know. We also don’t know any of their other lifestyle choices that could lead to plaque build up and heart trouble. How active were they? Did they exercise? Were they overweight? Were many of them diabetic? All of these questions could change how we interpret the results of the study. All the study does in point out a correlation. In this sample of people, those who ate more eggs had more cholesterol build up in their arteries. However, correlation is not causation. The fact that these thing happened in the same people does not mean that the eggs were the cause. We can not say this without accounting for all the other variables.

If you have an expected answer to a question then the chance that you will find evidence to support it is much more likely. This little story is somewhat silly (and possibly gross and a little cruel), but it illustrates the point nicely:

The scientist yells “JUMP!” at the frog and the frog jumps one meter.
Then he cuts off one of the frog’s legs, yells “JUMP!” and the frog jumps half a meter.
Then he cuts off another of the frog’s legs, yells “JUMP!” and the frog jumps a fifth of a meter.
Then he cuts off a third leg, yells “JUMP!” and the frog does not jump. He yells “JUMP!” again, and the frog does not jump.
“Aha!” he says. “I have my result!” So he carefully writes in his lab book: “When three legs are removed, a frog becomes deaf.”

I know this is a bit of an extreme example, but you get the idea. Now, Dr David Spence was one of the leaders of this study. His record shows that he believes dietary cholesterol to be bad for the heart, despite many new studies that suggest otherwise. Since that was what he believes to be true he went looking for evidence to support it and found what he was looking for. Dr. David Jenkins was another lead researcher, he just happens to be an ethical vegan, meaning he believes eating eggs to be morally wrong. It is possible he was also looking for a certain outcome.

This research was a type of study called an observational study. It was based on self-reporting, which the scientific community agrees is not a very accurate way to gather information. Unless I was to go look at my old meal plan, I can’t tell you what I ate this past month and certainly not how much. That is one reason why this style of study is not used to determine cause and effect. The type of study that does is called an intervention study. In this type one group of people is told to make certain lifestyle changes such as eat x number of eggs for breakfast, while another group is told to eat x amount of oatmeal. They are also to report exercise levels and other information so the researchers can factor those variables in to the study. In this more controlled manner it is possible to find cause-effect relationships. Two examples of such studies, found here and here, show that eating eggs does not harm your heart. There are many more.

So, the lesson here? Don’t believe every news article you read. Do your own research and ask trusted experts. Eggs have absolutely nothing in common with cigarettes. In fact, eggs are full of good nutrients, especially if they are from pastured hens. But for brevity’s sake, that’s another post.

*No frogs were harmed in the making of this post*

Sources:

http://www.washingtonpost.com/blogs/the-checkup/post/what-do-egg-yolks-and-cigarettes-have-in-common/2012/08/15/f5053b7a-e71b-11e1-9739-eef99c5fb285_blog.html

http://www.huffingtonpost.com/david-katz-md/eggs-health_b_1818209.html

http://frobinett.edublogs.org/2010/11/12/a-couple-of-interesting-examples-of-bias/