An immunotoxicologist by profession, Dietert speaks about these cutting-edge scientific matters with the zeal of the convert. Indeed, near the end of the book, we learn that he had something of a life-changing experience a few years ago. While visiting Germany for less than a week and eating whatever conference catering provided, Dietert discovered that he was losing weight and enjoying noticeable relief from two chronic conditions: gastric reflux and sinusitis. (The weight loss was all the more unusual because he was sitting in conferences for almost the entire trip.) Upon return home to the United States, he started experimenting, adding this or that component of his travel diet, until he stumbled upon a winning combination. It all but eliminated the inflammation he had suffered for decades.
Inflammation is a key function of the immune system, of course, where it helps fight infection and heal injuries. But it can end up attacking the very organism it was meant to protect. Dietert describes a Who’s Who of 21st-century afflictions, which he proposes can be alleviated, or even wiped out, if we repair or restore the microbiome. He believes that when our non-mammalian adverse goes awry, its first line of attack is to cause undesired inflammation in the rest of us, which in turn leads to NCDs like rheumatoid arthritis, obesity, irritable bowel syndrome, depression, allergies, arteriosclerosis, and many, many others. Taken together, they have become the plagues of industrial societies (and, increasingly, of developing nations that adopt our processed foods and other modern conveniences), the price we pay for more than 80 years of undeniable success in protecting ourselves and our domesticated animals from pathogens.
Most of us cling to the belief that cleanliness is next to godliness, and invest in enough shower gel and antibacterial soap to transform us into earthbound angels.
Dietert argues a strong case for a more holistic approach to medicine, and, hence, an expanded idea of what “human” means. He draws upon a solid body of evidence — the notes section is a fat one — making it relatively easy to ignore the volume’s flaws, which include Dietert’s tendency to repeat himself and a sometimes annoying degree of conviction in his own narrative.
What is less forgivable is Dietert’s sleight of hand regarding the amount of microbial biomass relative to the mammalian. His whole thesis rests on the mind-blowing disproportion of “them” to “us,” so the reader cannot simply ignore confusing or misleading data. In the introduction, Dietert states that “recent estimates [of relative numbers] of just bacterial cells range from a low of 57 percent to a high of about 90 percent of total human cells.” Yet, for the rest of the book, he does not mention cells at all, only the relative amount of our microbial partners’ genomic information, which, he insists, stands at 99 percent of our total genetic payload. The remaining 1 percent is all us. Those 10 million microbial genes contribute everything from digestive services to serotonin production in the gut (more than the brain does!), and cannot help but appear to dwarf our 22,000-gene human contribution. This may explain why Dietert chooses to support his case by counting genes, not cells. The wow factor is just that much stronger.
How much of you really is a bunch of bacteria, viruses, and so on, instead of mammal? At the beginning of 2016, Cold Spring Harbor Laboratory released a paper that corrected previous, frequently quoted claims that we are 90 percent not-us, by cell count. The real proportions could be closer to 50–50. The paper itself enjoyed its 15 minutes of fame (in science, debunking anything tends to be good copy), then faded from sight. What does Dietert have to say? Well, the strange thing is that not once in the entire text does he refer to the paper, even to disagree with it — but he cites it in the notes. Did he bury it back there because a bolder reference, in the text, would distract his readers and threaten to dilute his argument, namely, that we ought to re-visualize ourselves as superorganisms?
Perhaps that ratio, like age, like so much we obsess over, is just a number. Far more important is Dietert’s challenge to dominant paradigms. He wants to rid the scientific community of the idea that the natural world consists of nothing but essentially homogeneous individuals, all too often at odds with each other — and the virtues of this perspective are as important to medicine as they are to ecology.
Far more worthwhile pondering is what it means to be human. “No man is an island,” wrote poet John Donne, speaking of the social contract. His formulation can serve as a prescription for our increasingly fragmented world, but also for how we can think of our body and its relationship with the microbodies it encounters. It is engaging to imagine each of those countless islands out there as a vibrant, teeming, coral reef, with the potential to connect with all the others.