THE BLOG
05/07/2014 04:55 pm ET Updated Jul 07, 2014

Dietary Immunity Or How to Guard Your Underwear

If you have ever been to sleepaway camp, or sent one of your kids, you have wrestled with one of the more vexing challenges the universe has conspired to throw at us: How do you stay in your own underwear? What I mean is, in a communal laundry situation, how do you avoid inadvertently wearing somebody else's underwear, or them inadvertently wearing yours?

I suppose you may be wondering what this has to do with diet, immunity, or any topic related to my customary purview of health. Bear with me -- we'll get there. But for now, back to sleepaway camp.

So there I am, in my imagination, at sleepaway camp, committed to staying in my own underwear. One option I have is to inventory -- mentally, or in writing -- everyone else's underwear, and steer clear of it. Lacy black? Not mine. Pink with polka dots? Also not mine. Leopard skin? Tempting... but, no, not mine.

You get the idea. But I trust you also see the problem. At some point, it's quite likely that someone will have basic briefs in white or gray, just like mine. And the next thing you know, I'm in someone else's underwear.

Our immune systems (told you!) confront much the same challenge; just substitute "self" for my underwear, and "non-self" for everyone else's. The basic job of the immune system is to differentiate self from non-self, and keep the microbial equivalents of someone else's underwear out of the immunological analogue of our underwear drawer.

The immune system might, then, inventory the full complement of "non-self" in the universe, and defend against it. But unlike the portfolio of underwear at camp, which was challenging enough, this list is potentially infinite. Changes in our environments can introduce us to new bits of "non self." Genetic mutations can devise never-before-seen compounds. Chemical engineering can do the same.

Our immune systems have had millions of years to devise a suitable strategy, and we are only here because that challenge was successfully met. Rather than inventory all the potential "bad" stuff in the universe, both known and as yet unknown, the immune system does the more expedient thing: It establishes an inventory of "self." Everything lacking the "made on the premises" label is foreign.

That label comes in the form of surface proteins, known as histocompatibility antigens. They are, in essence, a code that in the language of immunity spells: "self."

And, in a rare demonstration that there is intelligent life down here, we have recognized that if this is what millions of years of evolutionary biology came up with, we were unlikely to do better. From whence, the answer to the sleepaway camp dilemma: Put your initials in your underwear! If you identify your own, you don't have to recognize everyone else's.

There are limits to even this good method. In a large enough sleepaway camp, there might be someone with my brand of underwear, in my size, who also happens to have my initials. For our immune systems, it is possible for foreign material to carry a code that overlaps substantially with our own. The result of such failures to differentiate self from non-self is autoimmune disease, although the full story of autoimmune disease is far more interesting than that. It's a tale expertly told in the book An Epidemic of Absence, about which I have commented before -- and which I recommend highly.

All of which leads (I know, you thought I had forgotten) to the absurd way we handle dietary health. Learning from neither summer camp, nor evolutionary biology, we focus preferentially on some particular savior, or even more often, scapegoat. Our dietary fixation du jour is inevitably of the "avoid this nutrient/ingredient/food and all will be well" variety.

But it's nonsense. And it's nonsense about which I am impassioned, because we are paying for it with literal lives.

Thinking we can get to healthful diets and the phenomenal benefits they could confer by fixating on some food item to avoid is like thinking we could stay in our own underwear by identifying the one particular variety -- say, that leopard-skin bodice -- we should avoid. If our immune systems functioned this way, our bodies would throw open the gates to every bit of foreign material that didn't happen to be today's public enemy #1. And had they done so, we wouldn't be here now; we'd be extinct.

The world is full of foreign compounds, and other people's underwear. It is also full of foods we'd be better off not eating. In none of these cases can we wind up where we want to be by fixating on the "one thing" we should avoid. In each case, immunity against bad results derives from identifying what belongs here.

Between the 1970s and now, the average inventory of an American supermarket has increased by some 30,000 products. There are new ones all the time. Trying to keep up with all the foods you really shouldn't eat would be a challenging, full-time job. But we don't even do that job well. Instead, by settling on any given scapegoat -- fat, saturated fat, sugar, fructose, carbs, gluten, grains -- we practically invite the food industry to invent a brand new way for us to eat badly. History suggests they are only too happy to comply. The business of business is business, after all. Why wouldn't you sell new versions of high profit junk when people are so eager to buy it?

My friends, let's stop buying it. Quite simply, we cannot fix our diets one nutrient at a time, or one food at a time by just adding this, or just avoiding that. There are limitless ways to eat badly, and every such fixation merely invites the next.

What we might do instead, at long last, is focus on the well-established fundamentals of eating well. If we would define healthful eating in terms of the foods we should eat routinely, and the sensible combinations in which we should arrange them, we would find ourselves substantially immunized against pecuniary mischief, unintended consequences, pop culture hucksterism, fashion, fads and folly. We could add years to life and life to years; love food that loves us back; and while we're at it, wear the right underwear.

-fin

Dr. David L. Katz has authored three editions of a nutrition textbook for health care professionals, is President of the American College of Lifestyle Medicine, was commissioned by Annual Review in Public Health to write the review article, Can We Say What Diet is Best for Health?; and is the author most recently of both Disease Proof, and the epic novel, reVision. He wears very dull underwear.

www.davidkatzmd.com

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