Preventive Medicine Column
Dr. David L. Katz
If I were to say “__________ & eggs” to you, what’s the first thing that comes to mind? Please hold that thought, as I attempt to unscramble the latest research about eggs, and health.
The study recently published in the journal Atherosclerosis suggests that egg ingestion not only increases the risk of heart disease, but that the association is as strong as that for cigarettes. I don’t believe either is true.
I have 5 reasons for my position: association; predisposition; intervention; aggregation; & adaptation.
This was a study of association, not cause and effect. This column began with a demonstration of what we “associate” with eggs- other foods such as bacon. Imagine if the people who ate the most eggs also ate the most bacon, and sausage, and ham. Since the current study did not control for other aspects of diet, it could be that eating a lot of processed meats was contributing to arterial plaque, with eggs having nothing whatever to do with it. This is called confounding. In the 1970s, studies of “association” generated headlines that coffee consumption increased the risk of pancreatic cancer! When issues of confounding were resolved, however, there was no such effect.
All research is biased, because all researchers are looking for something; all researchers have a predisposition. The only real defense against that is methods that eliminate bias- such as randomization, double-blinding, and placebo control. None of this is possible in an observational study of associations- which means there is a very high likelihood of finding whatever it is you are looking for. I don’t know the lead author of the current study, Dr. David Spence, personally. But his publication record indicates clear dedication to indicting dietary cholesterol for crimes against humanity’s arteries.
I do, however, know one of the other authors, Dr. David Jenkins, quite well. He is both a friend and colleague. I consider Dr. Jenkins a pre-eminent nutrition researcher, who has made seminal contributions to the field. I also happen to know he is an ethical vegan- whose devotion to this matter extends even to the avoidance of all leather.
Intervention studies, which can determine cause-and-effect, tend to trump observational studies, which cannot. In the context of a large body of evidence challenging the association between eggs and cardiac risk, my own lab has conducted three intervention studies. We have already published the results of two of them, one showing no harmful effects of daily egg ingestion in healthy adults, and the other showing no harmful effects in adults with elevated cholesterol.
Results of the third study, just completed, are not yet published. I can’t spill those beans here, but I can say something about it. It was a study of daily egg ingestion among adults with established coronary artery disease- and the opinion I am expressing in this column is informed by my review of the findings. Enough said.
My own labs findings are, as noted, in the context of a clear aggregation of evidence over recent years suggesting that dietary cholesterol is mostly, if not entirely, innocuous when isolated from the company it often keeps in the diet. The weight of evidence about eggs has, in my opinion, tipped decisively toward a “not guilty” verdict.
And finally, there is the context that makes sense of this: adaptation. Paleoanthropologists tells us that eggs have been part of the human diet back to the Stone Age.
I hasten to add I don’t really have a personal agenda about eggs, and certainly not in favor of them. I banished them from my own diet for roughly 20 years when the research evidence seemed to incline that way. I don’t like the way hens are treated on large ‘factory farms,’ and certainly don’t want to take a position that fosters the ill treatment of any animal. I am a strong proponent of a mostly-plant based diet.
But the truth about eggs and health is best revealed by research that subordinates such predilection and eggspectation to hard-boiled methodology. When that is done, I believe the egg is substantially…eggsonerated.
Dr. David L. Katz; www.davidkatzmd.com