Blog | Friday, May 17, 2019

Eggs, oxygen, and the perennially breathless state of nutrition

Are eggs good or bad for us now? Yes.

A recent meta-analysis, widely covered by media ever hungry for just such dietary provocations, reported that the more eggs people ate over time, the more prone they were to heart disease. This, inevitably, has been juxtaposed with the advice in the 2015 Dietary Guidelines to abandon a specific focus on dietary cholesterol and unleashed the predictable round of breathless expostulations about the deplorable state of nutritional science and understanding.

Actually, the deficiency is sense, not science, and worse still, the perennial neglect of the former when interpreting the latter. Absent sense, science doesn't work, minimally, because it generates answers to all the wrong questions.

I'll get back to eggs, and cholesterol, and where sensible interpretation of all the relevant data takes us momentarily. For the moment though, let's just breathe together…

Breathe, as in … be centered, and calm, and in the moment, and all that meditative stuff. But also, breathe because otherwise you will die in a matter of minutes. You need oxygen, in every breath, to live. So, best to breathe.

But now, let's consider what we know about oxygen and the related research evidence.

We know, for example, that people living all their lives at high altitudes, in the Andes and Himalayas, adapt to that stress by having oversized chest cavities and lungs, and by having unusually high hematocrits (the concentration of red blood cells relative to total blood volume). These responses to high-altitude living help compensate for the low concentration of oxygen up there, but they are otherwise ominous in their implications for health. A high hematocrit raises the risk of potentially lethal blood clots; oversized lungs can impair the function of other organ systems in the general neighborhood, from heart to liver.

OK, then: too little oxygen is bad.

But, hold your horses if not your breath. Too much oxygen is bad, too, maybe even worse. First, we have evidence of a potentially lethal condition, ARDS, when people receive excess oxygen while on a ventilator. Oxygen is in fact so highly toxic, it effectively scorches the very organ that processes it. Permanent lung injury can result from exposure to high concentrations of oxygen in relatively short order, a matter of days, and sometimes, just hours.

And, in some circumstances, an “excess” of oxygen will cause people in dire respiratory peril to stop breathing altogether. This one requires a bit more explanation.

Ordinarily, it is not oxygen levels that prompt us to breathe even while sleeping. Rather, it is levels of CO2 (carbon dioxide). The details here can get rather recondite rather fast, so let's keep in the shallows. C02 combines with water in the body in a way that releases acid (non-chemists, just trust me). The body regulates pH levels in the blood very strictly, because cells and enzymes can only function within a very narrow pH range (outside of that narrow range, we die, quickly). The result of all this is: the body strictly regulates CO2, rather than oxygen, and that dictates the compulsion to breathe, in most of us.

The exceptions are known as “CO2 retainers.” These are people generally with COPD (chronic obstructive pulmonary disease), typically as a consequence of long-term smoking. As the name implies, this disease is “obstructive,” and thus limits the ability to expel spent air from the body. That, in turn, results in abnormal retention of CO2, the principal component of spent air.

Over time, the body adapts to these higher levels of CO2, and even invokes other mechanisms involving the kidneys (don't ask; if you want the Full Monty, consider medical school) to keep pH as nearly normal as possible. But this comes at a cost: exposed constantly to abnormally high CO2, the body's native alarm that sounds “CO2 is high, breathe now!”, turns off. Perhaps the simplest way to think of this is that boy who cried wolf. With CO2 retention, that alarm never stops sounding, and the body learns to tune it out.

Under such circumstances, breathing of course goes on, but under new management. In this population, it IS oxygen that becomes the driver of breathing. As O2 levels fall, and the oxygen saturation of blood declines between breaths, this alternative stimulus goads breathing.

But here's the rub! This very population, people with COPD and CO2 retention, is very prone to bouts of respiratory distress that lands them in the hospital. When, for instance, someone in this condition gets bronchitis, the oxygen levels in their blood may fall to near a critical threshold (this threshold is a product of the oxyhemoglobin dissociation curve, and again, don't ask, just go to med school!). To keep them above that threshold, oxygen must be administered. But when enough oxygen is administered to rise above that dangerous tipping point, it can be enough to turn off the impulse to breathe entirely. Sometimes the window of therapeutic opportunity is agonizingly narrow.

So, too little oxygen, and someone in this state will asphyxiate, and maybe die. Too much oxygen, and they stop breathing, and maybe die.

So is oxygen essential or toxic, good or bad? Yes.

Is too much oxygen, or too little oxygen, lethal? Again, yes.

Were we to treat any other branch of science or medicine with the fatuous want of sense we apply to nutrition (and to be fair, sadly there are others we do, from evolution to vaccination, just to name two), we would be reaching the conclusion daily, in a flurry of fraught tweets and blogs, that we know nothing about anything. Based on the above, and utter confusion about oxygen, I can only infer we should declare the state of intensive care hopelessly mired in contradiction, and shut down every ICU in the country immediately. We are, after all, terribly confused about oxygen! Aren't we?

No, we are not. Not at all. We simply know that sometimes the truth has nuance. Sometimes the truth needs a little room to…breathe.

We know that all of the answers pertaining to oxygen are: it depends. The right amount of oxygen varies by circumstance. The right amount is vital. The wrong amount, which also varies by circumstance, is injurious.

Vexing though such nuance may be, defiant though it may be of our penchant for dualistic, Manichaeistic sound bites and simple-minded clickbait, it's the truth about oxygen. It's the truth about almost everything in science, and it's certainly the truth about food: actual understanding requires more than over-simplified, over-generalized summary judgment. It actually requires thinking, and interpretation, in context.

Sorry, but that's the truth our information-over-fed culture fails to chew, and refuses to swallow. And, yes, it's the truth about eggs.

The 2015 Dietary Guidelines Advisory Committee, and the subsequent Dietary Guidelines, never said that eggs were entirely innocuous, and certainly never said they were “good” for us. They simply said, based on the weight of relevant evidence, that they were not a helpful focus for the current dietary guidelines. Guidelines are intended to help fix what's broken, and as of 2015, most Americans were consuming dietary cholesterol below the recommended threshold.

Short-term intervention studies of egg ingestion, including several from my own lab (industry funded, by the way, for those who want that disclosed immediately), have indeed suggested eggs to be relatively free of acute harms across a wide array of relevant measures. Large, observational studies over long periods of time have suggested much the same.

But, and here's the nuance, the right, large observational studies also help us understand why this might be both true, and false. Consider, for instance, the prevailing, and utterly misguided, pop-culture notion that saturated fat has been redeemed and is good for us now. Actually, the two meta-analyses underlying this contention simply showed that across fairly narrow and fairly high ranges of saturated fat intake, rates of heart disease were high and rather constant.

A 2015 study by researchers at the Harvard School of Public Health explained why. When saturated fat in the diet is replaced with added sugar and refined carbohydrate, which is how most Americans have replaced it over recent years, it's a lateral move. We have no evidence that saturated fat is good for us now; we just have evidence that there's more than one way to eat badly, and Americans are committed to exploring them all. (Tell them what they've won, Johnny!)

Everything causing confusion about eggs is readily interpretable when some related sense is applied. Eggs and dietary cholesterol are not a major public health concern at present simply because we've got bigger problems: sugar, ultra-processed foods, saturated fat, and sodium to name a few.

Eggs and dietary cholesterol were never declared “good” for us; the best arguments have only ever been lack of harm. But whether lack of harm is good, bad, or in-between is entirely, and obviously dependent on: instead of what? In the typical American diet, eggs for breakfast may be replacing toaster pastries, donuts, or multi-colored marshmallows masquerading as cereal. That might well be trading up, both directly, and because eggs are nutrient rich, and satiating, and might blunt appetite.

On the other hand, eggs in the place of, say, my own standard breakfast of steel cut oats, mixed berries, and walnuts, would certainly be trading down. These foods are decisively good for us, and “not harmful,” relative to “overtly good,” is, well, comparatively harmful.

That, in turn, explains the results of the new meta-analysis. People with the highest egg intake may have been directly harmed by that excess dietary cholesterol. They may have been harmed by some of the company eggs tend to keep, such as sausage and bacon (although the researchers attempted to adjust for this). And they may have been harmed indirectly because more eggs meant less whole grains, whole fruits, whole nuts.

The new study drops the sky on neither us, nor Henny Penny. It scrambles our understanding of neither nutrition in general, nor eggs specifically. Rather, it does what any one study always does: invites the application of sense to the task of interpretation in context, and posing the relevant questions. Eggs, instead of what? What, instead of eggs? Eggs in the company of what other foods? How did diet patterns, diet quality, and lifestyle practices vary with egg intake? Absent this routine application of sense to science, we will be forever stuck in dietary Groundhog Day, using each news cycle to repudiate the epiphanies of the prior.

Folks, here's the harsh, stark, like-it-or-lump-it reality check: no volume of data will save the witless from themselves. Science will only ever work reliably in the hands of those who interpret it with a bit of basic (but seemingly quite uncommon) sense.

Is oxygen good or bad for us? Yes.

Are eggs good or bad for us? Yes.

Nutritional nincompoopery of the sort that dominates our culture? Bad, every time.

PS, My take on eggs: Whatever harm they might do is generally obscured by the bleak character of the typical American diet. To isolate and observe effects on, say, blood cholesterol, we must test them in the context of very high-quality, plant-predominant or exclusive baseline diets. I think they are better for us than much of what passes for food in America these days, but not nearly as good for us as whole grains, whole fruits, nuts and seeds, beans and lentils, or vegetables. And, yes, we should consider the treatment of hens, often subject to rather horrible abuse on large “factory” farms. If you do eat eggs, try to source them locally, from a farm you can visit, and where, maybe they even name the chickens. Failing that, at least confirm that no hens were confined, and clipped, and abused in service to your breakfast.

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 Linked In page.