kimchi
© Hyunwoo Sun/FlickrKimchi.
As researchers learn more about the human microbiome, there's increased interest in how diet influences the microbes that call us home.

One of the most intense areas of scientific study today is that of the human microbiome—that is, the microbial communities (and their genes) that form a vast, complex ecosystem on our skin and throughout our bodies. According to the National Institutes of Health's Human Microbiome Project (I love the thought of my tax dollars at work there), "these communities consist of a variety of microorganisms including eukaryotes, archaea, bacteria, and viruses. Bacteria in an average human body number 10 times more than human cells, for a total of about 1,000 more genes than are present in the human genome." In general, our resident microbes are endlessly responsive and versatile; because they evolve so fast (some reproduce every 20 minutes), they allow our bodies to adapt to changes as we age, for instance, or enter the late stages of pregnancy. I guess you could say it's a microbe's world, and we just live in it.

Because of their size, microorganisms make up only about 1 to 3 percent of our body mass, HMP goes on to explain, adding helpfully that that's two to six pounds in a 200-pound adult, with the largest concentration in the gastrointestinal tract. Even though we tend to equate the words microbe and pathogen, most of the trillions of microbes that inhabit our bodies aren't harmful; they are critical for maintaining health.
"They produce some vitamins that we do not have the genes to make, break down our food to extract nutrients we need to survive, teach our immune systems how to recognize dangerous invaders and even produce helpful anti-inflammatory compounds that fight off other disease-causing microbes."
They may even be implicated in health problems such as obesity and depression, according to microbial ecologist Rob Knight's 2014 TED Talk. Knight, one of the top scientists in the field, is also the cofounder of American Gut, the world's largest crowdfunded citizen science project. Participants—including Michael Pollan, who wrote about his experience with American Gut for The New York Times Magazine in 2013—learn how many of which species of microbes inhabit their bodies and in doing so also contribute data to researchers around the world who are studying how microbiomes affect human and environmental health. For $99, you too can join the party. I know I am going to, especially given the fairly recent addition of a puppy to our household. It's much easier thinking of all those pats, belly rubs, licks, kisses, and tick inspections as a way of acquiring a more diverse, and thus more resilient, microbiome instead of—well, you get the picture.


Comment: Some of my best friends are germs


The American Gut project has expanded to Britain, Australia, and as of this month, Asia. What is also expanding is the notion among consumers that whatever ails them will be prevented or cured by DIY microbe management, with solutions ranging from supplements or homemade, probiotic-rich sauerkraut and other fermented foods to at-home fecal transplants. Probiotics are live microorganisms that are intended to have health benefits when introduced into the body; prebiotics are nondigestible carbohydrates that act as food for probiotics. The term synbioticsrefers to the usage of bothprobiotics and prebiotics in various combinations.

Researchers have studied probiotics to find out whether they might help prevent or treat a number of health problems, including diarrhea caused by infections or antibiotics, irritable bowel syndrome, inflammatory bowel disease, allergic disorders such as eczema and hay fever, tooth decay, periodontal disease, colic in infants, liver disease, the common cold, and ragged cuticles. I made that last one up, but admit it—you weren't quite sure, were you?

Even though a global market for probiotic ingredients is projected to reach $46.55 billion by 2020, there is little scientific evidence so far that eating a few billion probiotic microbes in yogurt, kimchi, or fermented drinks such as kefir or kombucha has much of an effect on those trillions we have in our gastrointestinal tracts. Not that big food is shy about overreaching, mind you. Who could forget the "Activi-ahh" jingle from those commercials featuring Jamie Lee Curtis? "Activia eaten every day is clinically proven to help regulate your digestive system in two weeks," the voice-over claimed. After a Federal Trade Commission investigation (again, our tax dollars at work) into Activia and DanActive—a product advertised as helping people avoid colds and the flu—Dannon settled a false-advertising lawsuit to the tune of $35 million.

"Researchers still don't know which probiotics are helpful and which are not," states the NIH. Part of the difficulty in determining which probiotics might have a positive benefit is that they aren't all created equal. "For example, if a specific kind of Lactobacillus helps prevent an illness, that doesn't necessarily mean that another kind of Lactobacillus would have the same effect or that any of the Bifidobacterium probiotics would do the same thing. Although some probiotics have shown promise in research studies, strong scientific evidence to support specific uses of probiotics for most health conditions is lacking."

Still, although researchers have barely scratched the surface, it's interesting to see how those who are deep in the weeds have changed their diets. A number of the scientists Pollan interviewed told him that they had eliminated or cut back on processed foods, "either because of its lack of fiber [deleterious to the microbiome] or out of concern about additives. In general, they seemed to place less faith in probiotics (which few of them used) than in prebiotics—foods likely to encourage the growth of 'good bacteria' already present."

What about increasing our exposure to microbes in general? Well, I'll still thoroughly wash the produce I buy and avoid cross-contamination in the kitchen—but the rather wet chew toy that was just deposited in my lap (hint, hint)? No worries.