Nurturing Our Microbes

Each of us is a metropolis. Bustling about in everyone's body are tens of trillions of microbes. Some are descended from starter populations provided by mom during birth. Additional bacteria, yeasts, and other life forms hitchhike in with foods. By age 3, everyone's gut hosts a fairly stable, yet diverse, ecosystem.

Most of the tiny stowaways hide out in the gastrointestinal tract — the gut-stealing a share of everything we eat or drink. But that's only fair, because most of these bugs give as good as they take, explains microbiologist Jeffrey I. Gordon. They not only help us digest food, he says, but they also harvest nutrients, manufacture certain vitamins, kill germs, neutralize bacterial toxins, and modulate the immune system. Sickness, antibiotic therapy, or stress, however, can disrupt the ecological balance among gut dwellers — known as flora — diminishing their benefits.

Because these benefits are vital to health — and to averting disease — drug manufacturers are eyeing gut microbes as potential therapeutic targets. In the future, "pharmaceutical companies might be drugging your bugs, not drugging you," suggests Jeremy Nicholson of Imperial College, London.

In the meantime, over-the-counter therapies exist to bug, not drug, the bugs. Known as probiotics, these yogurts and other foods or dietary supplements introduce or replenish beneficial gut species in the digestive system (SN: 2/2/02, p. 72).

Probiotic microbes' role in fighting generic diarrheal disease is old hat, but in the past decade, other influences on human immunity and metabolism have emerged. Certain microbial supplements show the potential to reduce the severity of colds and other infections, temper body weight, and even help the elderly fight osteoporosis.

The rub: Research is showing that a probiotic's benefits can be very specific. In fact, it might be more appropriate to view these microbes as a cornucopia of diet-based, over-the-counter micro-pharmacists — each able to dispense only a few therapies or services.

But for all the promise that probiotics offer, they're no panacea, many researchers caution, and may even exhibit disturbing effects (see "Not without Risks," below). Within a given species, some strains may confer health benefits, others may not.

Yet when the right bug is ingested for a particular condition, even a small dose can trigger dramatic health benefits.

Dining partners

"The total number of microbes associated with our adult bodies exceeds the total number of our human cells by a factor of 10," says Gordon, of Washington University in St. Louis. So effectively, "we're sort of a superorganism — one that's 90 percent microbial."

Other animals have evolved a similar symbiosis with — or even dependence on — gut microbes, the scientist notes. Rodents born by cesarean section (so they get none of their moms' intestinal flora) and raised under germfree conditions end up smaller than normal, his group found — despite eating "about 30 percent more food than their microbe-laden counterparts." ...

•	Nurturing Our Microbes Cover Story Science News Online, Saturday, March 1, 2008 Byline: Janet Raloff