The ecosystem inside you (Some experts suggest that the widespread use of antibiotics, which kill good bacteria along with the harmful bacteria they target, could help explain the skyrocketing rates of asthma, obesity, and autism.)

[2]

AP Photo/NIAID, Agriculture Department
The ecosystem inside you
THE WEEK STAFF | MAY 11, 2013
Don't bacteria make people sick?
Many of them do, and antibiotics that kill them have saved countless
lives. But over the past decade, researchers have discovered that the
human body hosts 100 trillion mostly benign bacteria, which help
digest food, program the immune system, prevent infection, and even
influence mood and behavior. The bacteria living on and in us make up
our "microbiome," an ecosystem that plays a role, scientists believe,
in many conditions that genes and environmental factors alone can't
explain, including obesity, autism, depression, asthma, and even
cancer. The discovery of the microbiome, said Michael Fischbach, a
bioengineer at the University of California, San Francisco, has been
"very much like finding an organ we didn't know we had."

Where is the microbiome?
Bacteria thrive throughout our bodies — in our mouths and lungs, on
our skin and teeth, and especially in our guts. The Human Microbiome
Project, a government-supported effort to map our bacterial
ecosystems, has discovered that people harbor 10 bacterial cells for
every human cell. Every body hosts at least 10,000 different species
of bacteria, contributing up to five pounds to body weight. "Half of
your stool is not leftover food. It is microbial biomass," said
project director Lita Proctor. Last year scientists presented evidence
that everyone has one of three gut bacterial profiles, or
"enterotypes," characterized by high levels of specific bacterial
species. Some argue that enterotypes are as distinct as blood types,
and that learning more about them will help us design better drugs and
target them more effectively.

How do bacteria influence health?
Microbiome research is in its infancy, but there is already evidence
that an imbalance of gut flora may cause gastrointestinal problems
such as irritable bowel syndrome and Crohn's disease. Bacteria may
also help calibrate our basal metabolism. When obese people undergo
gastric bypass surgery to lose weight, scientists have observed, their
gut bacteria become more like those harbored by thin people,
contributing to weight loss. Microbes can even influence mental states
by encouraging neurons in the intestines to signal the brain to alter
hormone levels. Studies in mice have shown that changes in gut
bacteria can relieve — or cause — depression and anxiety. It has also
been shown that autistic children — who frequently suffer from
gastrointestinal problems — often carry a type of gut bacteria that
non-autistic children don't.

Why the difference in bacteria?
Some 80 percent of an individual's gut flora comes from his or her
mother. A newborn exits the womb microbe-free, but is colonized by the
mother's vaginal bacteria as it passes through the birth canal. Babies
born via caesarean section, it turns out, enter life with an entirely
different, and less diverse, collection of bacteria, which may help
explain why they're at increased risk of asthma, obesity, and type-1
diabetes. Breast milk, unlike formula, also delivers maternal bacteria
that help the immune system develop.

Can the microbiome change?
Yes, for good and for ill. Diet plays a major role in determining what
bacteria people host. A recent study found that when certain gut
bacteria feed on compounds in red meat or egg yolk, they produce an
artery-hardening compound called TMAO. People who rarely eat red meat
or egg yolks don't carry the same TMAO-producing bacteria and so can
eat those foods occasionally without increasing their heart disease
risk. Older people who live independently tend to have more diverse
microbiomes than their frailer peers who live in nursing homes — maybe
because of their different diets — but it's unclear whether a narrower
microbiome causes declining health or is a consequence of it.
Antibiotic use can also reduce gut flora. Researchers are still trying
to determine what factors "could set the microbiota in a good
direction versus a bad direction," said University of Colorado
biochemist Rob Knight. "There are very few cases where cause and
effect are known."

Can bacteria be used to treat illness?
In at least one case, they already are. C. difficile infections —
caused by a bacterium that can take over the gut — cause severe
diarrhea and kill 14,000 Americans per year. C. difficile is
notoriously difficult to eradicate with antibiotics. But researchers
have discovered that transplanting a healthy person's stool, via a
tube inserted into the patient's stomach, cures the infection almost
instantly by repopulating the patient's microbiome with healthy
bacteria. Tellingly, C. difficile infections often begin after a
person takes antibiotics to treat an unrelated condition. Some experts
suggest that the widespread use of antibiotics, which kill good
bacteria along with the harmful bacteria they target, could help
explain the skyrocketing rates of asthma, obesity, and autism.
"Whenever they are used, there is collateral damage, " said New York
University microbiologist Martin J. Blaser. "And we are only now fully
learning how severe that damage has been." Scientists are now trying
to figure out what constitutes a healthy microbiome, in hopes they can
treat health problems by tweaking the mix of a person's bacterial
species. "The prospects here are endless," Blaser said. "This is the
most exciting and important work of my lifetime."

The probiotics boom
Pills, drinks, and yogurts containing probiotics — live, beneficial
bacteria — have become big business. In 2011, global sales of
probiotics reached $28 billion and are expected to reach $42 billion
in 2016. But experts remain skeptical of commercial claims, often
unverified by clinical trial, that they bolster the immune system,
improve digestion, and generally optimize our health. A review of
probiotic research by scientists at Yale found that certain strains
did appear to reduce diarrhea and alleviate irritable bowel syndrome,
and other studies showed that they could shorten colds. But
researchers still aren't sure which bacterial strains are helpful for
which conditions, and how they interact with a given person's existing
microbiome. "The science has been shoddy and flimsy," said bioengineer
Michael Fischbach. Probiotics may well be the future of medicine, but
they should "be more complicated and also more rigorously tested than
today's probiotics," he says. "They'll be something that your doctor
prescribes."






http://m.theweek.com/article.php?id=243992