I have a special fascination with the human microbiome. I believe that understanding it will ultimately be one of the greatest, if not the greatest, medical achievement of the 21st century. But it will take the better part of this century to reach comprehension adequate for therapeutic use. In the meantime, it’s interesting to see the books being written about the intriguing bits we do know.
Below is a brilliant review from the Sunday New York Times of three new books on the human microbiome. The review is written by Sonia Shah, a science journalist and author whose books include “The Fever: How Malaria has Ruled Humankind for 500,000 Years” and “Pandemic: Tracking Contagions From Cholera to Ebola and Beyond,” to be published next month.
From the New York Times Book Review, Sunday, January 3, 2016
‘The Diet Myth,’ ‘The Good Gut’ and ‘The Hidden Half of Nature’
By SONIA SHAH
DEC. 28, 2015
Sometime before the age of 5 or so my son misheard the term “taste buds” and imagined, instead, that his mouth was alive with “taste bugs.” This came in handy for him when under fire for rejecting the variety of new foods we put on the table. It wasn’t his fault that he didn’t like broccoli and spinach, he’d explain, it was his pesky taste bugs.
Back then, we considered this mostly exasperating. Now, it turns out, the kid may have been right. Using the improved detection capacity of genetic sequencing techniques, scientists have discovered that 100 trillion microscopic creatures live in and on the body, influencing everything from the intensity of our immune responses and our moods to our dietary preferences and propensity to gain weight.
The most prolifically microbe-rich organ is the large intestine, which in the average American is home to a dynamic ecosystem of 1,200 different bacterial species. These creatures (collectively known as the microbiome) produce a slew of compounds, from toxins that cause inflammation and are associated with heightened heart-disease risk to critical vitamins, the mood-regulating hormone serotonin and compounds that suppress hunger and reduce glucose and insulin levels in the blood.
Popular and scientific interest in how the microbiome might be manipulated through diet, supplements and transplants to improve health and treat disease has exploded in recent years. It’s now the subject of a spate of new books. In “The Diet Myth: Why the Secret to Health and Weight Loss Is Already in Your Gut,” the genetic epidemiologist Tim Spector describes how gut microbes interact with genes and diet. The book is structured as a takedown of diet myths, but it’s much more than a self-help advice book. It’s witty, well-written and broad-ranging, littered with fascinating factoids and case studies. Spector thoughtfully explains the strengths and weaknesses of the available evidence, drawing on research on gut microbes as well as his long-running studies on the genetics of twins and his own often hilarious experiments with various diets.
In Spector’s telling, gut microbes are neither good nor bad: The part they play in health and disease is dynamic and contextual. For other authors, the story is a little simpler. Gut microbes are the good guys, and they’re under assault. In “The Good Gut: Taking Control of Your Weight, Your Mood, and Your Long-Term Health,” the Stanford University gut microbiome researchers Justin Sonnenburg and Erica Sonnenburg describe how the Western lifestyle methodically diminishes the diversity of the gut microbiome. Easily digestible processed foods starve gut microbes of nutrients, highly sanitized environments deprive them of microbial visitors, antibiotics knock them down and Caesarian sections distort their populations. By doing so, they argue, these hallmarks of the Western lifestyle are “disastrous” and partaking of them tantamount to “a game of Russian roulette” with our health.
To wit, reduced microbial diversity in the gut is associated with — though not proven to be a cause of — an increased risk of obesity, diabetes and irritable bowel syndrome. If you knock down the gut microbes of children before the age of 2 with a broad-spectrum antibiotic, for example, the risk that they’ll become obese jumps by 11 percent. Farmers have long known the same to be true in livestock, which is why 80 percent of the antibiotics consumed in this country are fed to animals to fatten them for market; Spector speculates that the environmental runoff from this practice may be an underlying cause of the childhood obesity epidemic. And babies born via C-section whose gut microbes are seeded by the hands of nurses rather than the birth canals of their mothers have a 20 percent higher risk of food allergies and asthma.
For the Sonnenburgs, this means that a diverse gut microbiome is the key to good health. But at the same time, aspects of the modern Western lifestyle that have reduced microbial diversity in the gut have increased longevity, too. Processed foods have cheaply filled bellies, sanitary methods that separated human waste from food and drink have prevented epidemics of disease, and antibiotics have saved us from life-threatening infections. This may be why, in part, the hunter-gatherer tribes whose highly diverse gut microbes the Sonnenburgs mention admiringly have a life expectancy at birth that is about half that of the typical, microbially depleted American. Had the Sonnenburgs incorporated these facts into their argument, a more nuanced view of microbes in human health might have emerged.
David R. Montgomery and Anne Biklé, in their ambitious and prodigiously researched book, “The Hidden Half of Nature: The Microbial Roots of Life and Health,” take an even more romantic view of the microbial world, drawing connections between the assault on microbes in agriculture and the assault on microbes in the body. Montgomery is a geomorphologist and the author of several books on geology, and Biklé is an environmental planner. Oddly, they don’t use their outside expertise to enrich and extend their explorations of the microbiome. Instead, they strike the incredulous tone of outsiders, amazed, astounded and shocked (sometimes in the same paragraph) by the wonders of the microbial world. Their excitement about the microbiome is undoubtedly justified: Its discovery calls into question all manner of underlying assumptions about the nature of disease, our relationship to the natural world and even what it means to be human. But too often, their defense of the microbiome reads like a cross between a regurgitated college textbook and the promotional copy on the back of a bag of compost. It is this kind of boosterism that has allowed the rapidly growing probiotics industry to claim their microbe-rich capsules do everything from improving immunity to aiding weight loss, without proving that any of that is so.
The truth is that for now, proven effective new therapies based on manipulating the gut microbiome concern diseases specific to the gut itself, such as C. difficile infections. When researchers have tried to, say, alter gut microbes in order to treat obesity — for example by transplanting the gut microbes of lean people into obese ones — they’ve failed. It may be that studies to date have been too small to be conclusive. Or it may be that there’s a lot more involved in obesity and other conditions than the activities of gut microbes.
Still, whether the furor over the gut microbiome leads to revolutionary new therapies or fizzles, one thing is for sure. Since the dawn of germ theory in the late 19th century, Western medicine has characterized microbes primarily as malevolent invaders to be repelled with antiseptic techniques and destroyed by microbe-killing drugs. That made sense, given that the ones scientists could most easily detect — the microbes that grew in petri dishes in the lab — were also the ones responsible for dramatic diseases such as tuberculosis and cholera. Now, in light of the vast scale of the noninvasive, non-disease-causing microbes living within, that reflexive antimicrobial approach makes far less sense. It’s time for a reboot.
THE DIET MYTH
Why the Secret to Health and Weight Loss Is Already in Your Gut
By Tim Spector
318 pp. The Overlook Press. $28.95.
THE GOOD GUT
Taking Control of Your Weight, Your Mood, and Your Long-Term Health
By Justin Sonnenburg and Erica Sonnenburg
301 pp. Penguin Press. $27.95.
THE HIDDEN HALF OF NATURE
The Microbial Roots of Life and Health
By David R. Montgomery and Anne Biklé
Illustrated. 309 pp. W.W. Norton & Company. $26.95.
A version of this review appears in print on January 3, 2016, on page BR9 of the Sunday Book Review with the headline: Inside Job.