Wednesday, March 4, 2015
There seems to be a whole lot of passion in response to the recent disclosure that this year's Dietary Guidelines Advisory Committee is recommending we stop fretting about cholesterol. Note that the committee merely advises, so these are not yet the official dietary guidelines for Americans. Famously, the politicians have the final say there.
That passion over cholesterol runs in both directions, with enthusiasts of more animal food intake, Paleo, dieters, for instance, feeling vindicated; and my vegan friends contending that an excess of cholesterol must have scrambled the brains of the Advisory Committee members, and prevented them from thinking clearly.
The timing was, depending on your point of view, fortuitous or calamitous for me, as my lab just published our third study of egg ingestion, this one showing no discernible harms from daily intake of two eggs for six weeks by adults with established coronary artery disease. In prior studies, we had shown similar lack of any discernible harm in healthy adults, and in adults with high blood cholesterol. The concurrence of these two things meant a barrage of media interviews for me, including the Today Show.
I hasten to note, as others apparently have with an insinuation of impropriety, that these studies were funded by the Egg Nutrition Center. That matters far less than people think, although there is some literature suggesting systematic bias with industry funded studies, and other literature refuting that. We might pause to note that almost every FDA approved drug we've got, great, good, bad, and ugly, is courtesy of pharma-funded research. Since it costs nearly a billion dollars to bring a drug through the pipeline to FDA approval, the process would slow to a crawl if it all depended on NIH funds. All any righteous indignation over industry funded food research does, in the absence of the same over drug studies, is further shift the balance in our culture away from food as medicine, and toward medicine as medicine. I don't think that trend really needs any help.
As for industry funded research, yes, it does mean the funder is biased, and is hoping for a particular outcome. What people tend to overlook is that the NIH, or the CDC, is a biased funder, too. No entity wants to spend its research dollars only to show what doesn't work. When peer reviewers decide where NIH should send tax payer dollars, a central element, and I know, because I've been a reviewer, is the likelihood of a positive outcome. Every funder of research invests on the basis of a hoped for outcome.
If, in all cases, both researcher and funder are “hoping” for a particular outcome, that means they are biased; and so we are. Is this more so when the funder has a stake in the product? I suppose, but it's a difference of degree, not kind. What really matters, then, is not the bias in the hope, but the defense against bias in the methods.
We won't go deeply into these weeds, there are textbooks on the subject for those inclined to do so, but suffice to say that the relevance of randomization, blinding, control groups, intention-to-treat analysis and other such methods all derive from researcher bias. If we were utterly objective ourselves, we would be less dependent on methodologic defenses against bias. But since we all have hopes and expectations, it is methods that defend against biased research outcomes. The other critical consideration is lack of censoring. A funder with a stake in the outcome might like to suppress bad news; research contracts should always preclude that option.
Ours do. I will only sign a research contract that protects our right, and obligation, to publish, no matter the outcome. Such were the contracts we signed with the Egg Nutrition Center. And, of course, we used the customary methods to defend against biased outcomes: randomization, blinded analysis, control group, and intention-to-treat analysis, all detailed in the published papers. Moving on.*
I was interested in studying eggs NOT because I think anyone in America is egg deficient, but because I think nutritional epidemiology has a dangerous blind spot. When we advise people to stop eating X, we generally fail to ask: what is the Y they will wind up eating instead? (And vice versa.)
You get a sense of the answer, though, on every cardiac care ward. Eggs, of course, have long been banished; Egg Beaters may show up on occasion. But bagels, muffins, Danish, pancakes, sugary cereals and other dubious fare is de rigueur. America gave up eggs, and started running on donuts.
A food in a diet, then, is like a pebble in a pond; the reverberations matter. I remain uncertain about the relevant reverberations of egg ingestion. We have a study ongoing now to look at that very question: in general, is overall diet quality better when eggs are routinely included, or excluded? Stay tuned.
As for the current status of dietary cholesterol, and by extension eggs, here are my reflections, over easy:
1) For most of the people most of the time, dietary cholesterol appears to be innocuous or nearly so. That is what studies suggest, and also makes sense in anthropological context. Eggs, and cholesterol, have apparently always figured in the Homo sapiens diet, much more so than saturated fat, which is at quite low levels in the flesh of wild animals. That is a good reason to de-emphasize cholesterol restriction, but should not be misconstrued for a reason to un-restrict its emphasis. I have not heard anyone suggest that the average American is egg deficient, and I certainly don't think they are.
2) Advocates of vegan diets point out that cholesterol/egg ingestion does raise blood cholesterol in vegans. In other words, if the baseline diet is free of cholesterol, as a vegan diet would be, adding cholesterol to it shows up in the blood. Against the backdrop of a typical American or European diet, no such effect is generally seen. The obvious questions here, then, are: so what, and for whom does the alarm bell toll?
Removing an emphasis on cholesterol from the dietary guidelines is hardly likely to induce vegans to start eating eggs, since many are more motivated by the highly questionable ethics attached to the treatment of hens (and right they are!) than by the nutritional issues anyway.
While studies suggest adding cholesterol to vegan diets raises blood cholesterol, there are no studies, to my knowledge, to show that doing so, in the absence of other changes to the diet, raises rates of heart disease or other ills. That's really what matters.
Finally, the Dietary Guidelines Advisory Committee is advising on the dietary guidelines for all Americans. I tried to find what percentage of Americans are vegan, and wound up with about 2.5%. In contrast, the typical American diet is consumed by, well, the typical American, meaning almost everyone else. The committee is not suggesting that the 2.5% add eggs; but they are saying that the 97.5% may not derive any benefit from systematically excluding them.
In the context of the typical American diet, eggs have many potential virtues. They are versatile, intrinsically portion-controlled, convenient, and portable. They are a perfect protein source, and as such, generally highly satiating (i.e., produce a lasting feeling of fullness) which might help with appetite and weight control. They are rich in a variety of nutrients, including some important shortfall nutrients, such as choline and biotin.
As for whether adding eggs to the diet is a good or bad idea, the obvious answer is, I think, the correct one: it depends.
If eggs replace deli meats, for instance, as a source of protein minus the many adulterations, it is trading up. If eggs replace donuts or Danish or muffins for breakfast, that is trading up as well. But should eggs replace, for example, a breakfast of steel cut oats, mixed berries, and walnuts? Hell no!
Why the exclamation? Because lack of harm does not equal evidence of benefit! This is the very mistake we seem inclined to make with saturated fat. A meta-analysis shows that rates of heart disease in the U.S. are just about constant at outrageously high and unnecessary levels whether we eat a bit more saturated fat and a bit less sugar, or a bit more sugar and a bit less saturated fat, and somehow that morphed into: eat more butter. What's the prize? Apparently a different way to get to the same, high risk of heart disease.
We do not want to make a similar mistake about eggs, or cholesterol. In my opinion, the Dietary Guidelines Advisory Committee is right about the absence of harm from cholesterol for the average American (although not the average hen).
But to my knowledge, they are not suggesting there is evidence of specific demonstrable benefit from eating more eggs. In contrast, we have exactly such evidence, lower rates of heart disease, diabetes, stroke, dementia, cancer, and so on, associated with higher intake of vegetables, fruits, whole grains, nuts and seeds, olive oil, and fish. Why aspire to lack of harm when we have evidence thatwholesome foods in sensible combinations can help us slash our lifetime risk of heart disease by some 80 percent?
Whether adding eggs to your diet will confer benefit, harm, or neither, almost certainly depends on what you are now eating instead of eggs, and what eggs would be displacing. I think we also do all have cause to care about how hens are treated, a topic recently addressed well by Mark Bittman.
We seem to like our dietary guidance oversimplified, and sunny side up. Inevitably, though, the details can be a bit deviled. It makes sense to stop focusing on cholesterol restriction. But should you eat more eggs? It depends.
*For those who care to know, my personal bias has always run against eggs, not for them. The son of a cardiologist who respected the apparent consensus of my senior colleagues, I believed we knew dietary cholesterol to be a bad actor, and banished eggs entirely from my own diet for more than 20 years. I only added them back when the weight of evidence clearly tipped the other way. I added them back very selectively, however. I eat them occasionally, and when I do, they are organic, locally sourced, and from hens treated kindly, eggsclusively! Nor have eggs replaced my standard breakfast of mixed berries and other fruits in season; walnuts; whole grains; and non-fat, plain Greek yogurt. Now you want to talk about grains, or dairy? No whey! Topics for other days.
David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.
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