The battle of the bulge may be won and lost
by the microbes in your digestive system.
EVER nO TiCE HOW SOmE PEOPlE diet and
exercise like crazy but can’t seem to slim down,
yet your best friend eats whatever she wants
without gaining a pound? You may blame it on
genetics, but you’d be only half right. Because
the genes to blame may not be yours.
“Some of the things you think are influenced
by your own genes are actually controlled by
microbial DNA,” says Rob Knight, professor in
the UC San Diego School of Medicine and Jacobs
School of Engineering. Knight is an expert in the
human microbiome—the genetic makeup of all
the microbes that live in and on us. He and other
researchers have discovered that microbes in
our guts play a big part in our health, especially
In fact, Knight can tell if you are lean or obese with
90 percent accuracy just by looking at the microbe
populations living in your intestines. A look at
your genome could yield only 60 percent accuracy.
Surprising? Consider this: our bodies contain
about 300 times more microbial genes than
human genes. And while 99.99 percent of those
human genes are the same from person to person,
our microbiomes are radically diverse—we share
only 10 percent in common with each other.
Researchers have found that an organism’s
weight can be altered by differing gut microbes.
Mice that received a microbial transplant from
an obese person gained weight, while mice
receiving transplants from lean people did not.
Turns out those “lean” microbes help the mice
digest food more efficiently, while the “obese”
microbes appeared to influence behavior—
the mice that received them ate more.
What’s next? Knight and colleagues are creating a
special facility at UC San Diego to design microbial
communities that prevent or reverse weight gain.
Knight also dreams of a day when—wait for it—a
“smart toilet” sends a microbiome readout to your
phone and your electronic medical record every
time you flush. Such information could determine
if you’re getting healthier or unhealthier, and also
come with advice on how to stay in good shape.
KEEP yOuR gu T HAPPy
Rob Knight’s tips for
a mighty microbiome.
FOLLOW YOuR GuT
Avoid taking unnecessary
Eat lots of leafy green and
brightly colored vegetables,
fermented foods and fiber.
Intestinal bacteria turn fiber
into butyrate, a metabolite that
reduces inflammation and feeds
the cells that line the gut.
Limit fried foods, artificial
sweeteners and other highly
processed foods, which can
decrease microbial diversity.
BY HEATHER BuSCHMAN, PH.D. ’08