Why Gut Bacteria Is Good for You

The trillions of gut bacteria that live in our bodies are often the unsung heroes of our good health. Here’s what happens when we disrupt their habitat.

By Sharon Begley
Also in Reader's Digest Magazine October 2013

Where Good Germs Begin
It’s worth taking a step back to cover the basics, which start with birth. The bacteria and other microbes you enter the world with come from your mom’s skin (if you were a Cesarean baby) or birth canal. “At first, the microbiota all over your body resemble your mother’s,” says Knight. “We don’t know how fast the microbiota of the skin, gut, or nose change, but within two or three years, they’re like an adult’s,” having picked up microbes from air, water, clothing, and diet.

This last part is vital: What we eat shapes what microbes our guts harbor. In 2010, a study found that Japanese people have bacteria that digest nori, the seaweed in sushi. Westerners don’t. Why? The Japanese consume lots of seaweed, which contains marine bacteria, which digest nori. “What you eat,” says microbiologist Justin Sonnenburg of Stanford University School of Medicine, is “one of the major determinants” of your gut microbiota.

Cultivate A Healthy Gut
Where this leaves someone who wants to encourage a healthy microbiota isn’t yet clear. One obstacle: “Nobody knows what an ideal human microbiome is,” says anthropologist Jeff Leach. Last year he launched American Gut, a crowdsourced research project that invites anyone to request a kit ($99), basically a superlong Q-tip that you use to swab used toilet paper and return for analysis. A questionnaire asks about habits and lifestyle: what pets you have, whether you have taken antibiotics recently, what you ate over the past few days, and other behaviors thought to affect the gut microbiota. In return, you get back the list of your gut microbes and how you compare with other people.

Until scientists can give the recipe for healthy microbiota, it pays to heed the advice of mainstream medical groups, which adviserestricting antibiotics to only must-have circumstances, not every cough and sniffle. Consider antibiotic-free meat. “The scorched-earth outcome of many broad-spectrum antibiotics is analogous to spraying poison all over your backyard and waiting to see what grows back,” says Leach.

In both cases, “invasive and maybe not-so-good species” can move in, with harmful results. Be wary of manufacturers making exaggerated claims about probiotics and prebiotics. While some are supported by clinical studies, others “greatly outstrip the scientific evidence,” says Knight. But just because commerce has galloped ahead of current research doesn’t mean there is no scientific basis for manipulating the microbiome to improve health. “We can’t change our first genome, the one we inherit from our parents,” says Knight. “But we can change the second, the microbiome. And that holds real promise.”

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