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8/17/2014 @ 8:00AM
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A Different Kind Of Gut Feeling: How Intestinal Bacteria Could Manipulate Your Brain
The next time you can’t figure out why you’re suddenly craving a huge
slab of ultra-decadent chocolate cake—consider the possibility that
it’s not just you doing the craving. New
research suggests that the armies of bacteria living in our guts can pull the strings in our brains to get what they want.
We’ve all heard about the bacterial universe within our bodies, but
what’s less well known is just how vast this universe is in comparison
to the rest of us: bacteria outnumber all of the cells in our body 100
to 1. And just like us, certain bacteria have a taste for certain
nutrients, and they’ve developed ways of influencing their hosts to
deliver more of their preferred vittles to the dinner table.
“Bacteria within the gut are manipulative,” said Carlo Maley, PhD, director of the
UC San Francisco Center for Evolution and Cancer and
study co-author. “There is a diversity of interests represented in the
microbiome, some aligned with our own dietary goals, and others not.”
How this happens is still an unfolding story, but it’s thought that
bacteria release chemical signals that are carried along the
vagus nerve—the
nervous system superhighway that runs from the digestive system all the
way to the base of the brain. These signals may affect our moods and
appetites, and influence us to get more of what the bacteria crave into
our mouths.
“Our diets have a huge impact on microbial populations in the gut,”
Maley said. “It’s a whole ecosystem, and it’s evolving on the time scale
of minutes.”
A strain of bacteria found only in the guts of Japanese people, for instance, has evolved to specifically
digest seaweed,
a normal part of Japanese diets. In the same way, certain bacteria
subsist on fats and sugars in diets more heavily laden with those items.
It’s theorized that if bacteria want more sugar, they use a chemical
carrot and stick approach; certain chemicals cause us to feel bad until
we ingest the sugar, and others perk up our mood as a reward for
delivering the goods.
“Microbes have the capacity to manipulate behavior and mood through
altering the neural signals in the vagus nerve, changing taste
receptors, producing toxins to make us feel bad, and releasing chemical
rewards to make us feel good,” said study co-author Athena Aktipis, PhD.
The good news, the researchers tell us, is that we can influence changes in our gut dwellers through dietary choices.
“Because microbiota are easily manipulatable by prebiotics,
probiotics, antibiotics…and dietary changes, altering our microbiota
offers a tractable approach to otherwise intractable problems of obesity
and unhealthy eating,” the researchers wrote.
There’s a growing base of scientific literature supporting the claim. A
few studies have shown that probiotics can decrease anxiety levels in mice, and last year researchers from UC Los Angeles
published results
showing that the brains of people ingesting a probiotic for four weeks
had less activity in brain areas associated with excessive anxiety. It’s
theorized that the probiotic altered the bacterial landscape in the
gut, with the effect of changing chemical signals sent to the brain.
This is, of course, just the beginning of a lengthy investigation
into the relationship between our intestinal microbiota and the brain,
but so far it seems quite plausible that not all of our appetites are
our own.
The
study was published in the journal
BioEssays.
You can find David DiSalvo on Twitter @neuronarrative and at his website The Daily Brain. His latest book is Brain Changer: How Harnessing Your Brain’s Power To Adapt Can Change Your Life.
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