The Them In Us
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My native inclination this time each year is to turn my attention from matters purely medical, and dwell somewhat preferentially on the humanistic: peace on earth, good will toward men (and women), and all that. ‘Tis the season for it, after all; the season of light and nativity, generosity and hope.

But I find all of that a bit harder this year, for it is also the season of our particular discontent, political and otherwise. Wherever we reside on any given spectrum of party, preference, or ideology, the rifts between us are on painful display. We are a house, a nation, and even a world much divided.

Struggling, then, to make my customary case for solidarity among the crowds of us, I turn this year to the solidarity among the crowd within each of us for some help. I mean our microbiome, and the particular goad to make that the focus of this homily is a recent commentary in JAMA, reflecting on the potential importance of those bacteria, and their genes, to the risk for, and management of, rampant obesity and diabetes.

The microbiome, as you likely know, refers to the vast village within, necessary indeed not only to raise a human child, but to sustain a human adult. Trillions of bacteria inhabit every one of us, and it is doubtful we could live at all were it not so. The exact numbers are a topic of some controversy, as is the margin by which our bacteria outnumber our cells; but that they do outnumber our cells is established. The human component of every human is something of a rounding error relative to the bacterial.

That is all the more so when genes are considered. As the JAMA article indicates, bacterial genes may outnumber our own by two to three orders of magnitude. That’s a big deal, because those genes manufacture compounds that become part of our inner worlds, just as the products of our own genes do. We are massively influenced, in every aspect of our physiology and metabolism, by the citizens of a diverse internal community.

How diverse? That’s the most interesting part of all this. Biological diversity is best measured at the level of DNA, certainly not appearance. Where it counts, almost all biological diversity is expressed by bacteria. Stated differently, the deep, meaningful biological diversity among bacterial species is far greater than the diversity among all other living things, including both plants and animals. Down near the bedrock of biology, penguins and pine trees are not only more alike, but almost indistinguishably similar, compared to the diversity just among bacteria. That invites us to ponder the comparative similarities between any two of us: Palestinian and Israeli, perhaps, Hindu and Muslim, male and female, black and white.

In the case of the microbiome, that astonishingly diverse community, itself only a sliver of the diversity among all bacteria, functions in stunning solidarity with both itself and us, the host. Our bodies provide the real estate those bacteria call home, and deliver to them their essential sustenance. They, in turn, mix their gene products with our own, altering everything from the integrity of our cells and tissues, to the balance of our many hormones.

It is indeed now clear this influence pertains powerfully to the risk of such conditions as obesity and diabetes. When, for instance, the bacterial flora from mice “designed” to be obese are transferred into lean, healthy mice, they can make those mice obese as well. The same works in reverse. Much the same is true of diabetes and other conditions, and similar patterns seemingly pertain to humans, although that evidence is rather less emphatic to date for the predictable reasons.

But important as the microbiomial influence surely is, I think we tend to get a bit carried away. Yes, a salutary balance of bacterial flora tends to favor a lean and healthy host; but so, too, do eating genuinely well and exercising routinely. Eating well and being active may not make every body lean, but when they are truly done, they truly work far more often than not.

There was very little obesity or type 2 diabetes 100 years ago, and virtually none in children. Was that because our predecessors had deep and ancient knowledge we’ve lost of the care and feeding of the microbiome? Of course not; they knew nothing of it. Knowledge of the microbiome and its importance is very modern.

What’s clear is that what’s good for the real estate is good for the residents, as much as vice versa. So, yes, our healthier ancestors almost certainly did have healthier microbiota. But tempting as it is to think we need to know what to feed our microbiota to make ourselves well, history and epidemiology indicate the opposite is true. When humans take good care of themselves, they tend to thrive. Presumably, so too do our symbionts, if only by happenstance.

I pay close attention to the fascinating and fast evolving literature on the microbiome, and certainly agree we cannot be well if there isn’t balance and relative harmony there. In rare circumstances, effective treatment of human ills may require direct attention to microbiomial imbalance.

But most of the time, that isn’t the case. Certainly, appreciation for the microbiome is not an invitation to ignore what we already know about promoting, protecting, or restoring our own health. Diet and exercise and healthy living work reliably to promote health and prevent disease, whether or not influence on the microbiome is part of the pathway. People can be healthy with no knowledge of taking care of their bacterial residents. Rather, they take care of those bacteria accidentally by taking care of themselves. As our knowledge of, and respect for, the microbiome evolve, we are well advised to bear this in mind- lest the whole endeavor become an exercise in procrastination.

Speaking of evolution, these reflections attest to both the power of it in biology, and our need for it in modern culture. The dizzying biological diversity of bacteria is testimony to evolutionary forces, as is our symbiotic relationship with trillions of those organisms.

To combat obesity and diabetes, and the other great scourges of modern epidemiology, will require that our perspective evolve past a choice between pursuing the details we don’t have, and applying the reliable knowledge we do. The next, great opportunity to add years to lives, and life to years, resides in the domain where those two are reconciled.

But advances in health offer little to cheer if we cannot find our way to reconciliations among ourselves. To combat the arguably greater scourges of division, distrust, and hate, we must evolve a perspective that takes us past us and them, to common cause. Perhaps the “them” within each of us can help, for they remind us that in the vast sweep of biological diversity, all of humanity is a very close-knit family.

Families, of course, can differ- but love generally prevails. May it be so. Happy holidays, cousin.


Director, Yale University Prevention Research Center; Griffin Hospital

Immediate Past-President, American College of Lifestyle Medicine

Senior Medical Advisor,