Got food cravings? What's living in your gut may be responsible

Date:
April 20, 2022
Source:
University of Pittsburgh
Summary:
New research on mice shows for the first time that the microbes in
animals' guts influence what they choose to eat, making substances
that prompt cravings for different kinds of foods.



FULL STORY ==========================================================================
Eggs or yogurt, veggies or potato chips? We make decisions about what to
eat every day, but those choices may not be fully our own. New University
of Pittsburgh research on mice shows for the first time that the microbes
in animals' guts influence what they choose to eat, making substances
that prompt cravings for different kinds of foods.


==========================================================================
"We all have those urges -- like if you ever you just feel like you
need to eat a salad or you really need to eat meat," said Kevin Kohl,
an assistant professor in the Department of Biology in the Kenneth
P. Dietrich School of Arts and Sciences. "Our work shows that animals with different compositions of gut microbes choose different kinds of diets." Despite decades of speculation by scientists about whether microbes
could influence our preferred diets, the idea has never been directly
tested in animals bigger than a fruit fly. To explore the question, Kohl
and his postdoc Brian Trevelline (A&S '08), now at Cornell University,
gave 30 mice that lacked gut microbes a cocktail of microorganisms from
three species of wild rodents with very different natural diets.

The duo found that mice in each group chose food rich in different
nutrients, showing that their microbiome changed their preferred diet. The researchers published their work today in the Proceedings of the National Academy of Sciences.

While the idea of the microbiome affecting your behavior may sound
far-fetched, it's no surprise for scientists. Your gut and your brain
are in constant conversation, with certain kinds of molecules acting as go-betweens. These byproducts of digestion signal that you've eaten enough
food or maybe that you need certain kinds of nutrients. But microbes in
the gut can produce some of those same molecules, potentially hijacking
that line of communication and changing the meaning of the message to
benefit themselves.

One such messenger will be familiar to anyone who's had to take a nap
after a turkey dinner: tryptophan.



========================================================================== "Tryptophan is an essential amino acid that's common in turkey but is
also produced by gut microbes. When it makes its way to the brain, it's transformed into serotonin, which is a signal that's important for feeling satiated after a meal," Trevelline said. "Eventually that gets converted
into melatonin, and then you feel sleepy." In their study, Trevelline
and Kohl also showed that mice with different microbiomes had different
levels of tryptophan in their blood, even before they were given the
option to choose different diets -- and those with more of the molecule
in their blood also had more bacteria that can produce it in their gut.

It's a convincing smoking gun, but tryptophan is just one thread of a complicated web of chemical communication, according to Trevelline. "There
are likely dozens of signals that are influencing feeding behavior on
a day-to-day basis. Tryptophan produced by microbes could just be one
aspect of that," he said. It does, however, establish a plausible way
that microscopic organisms could alter what we want to eat -- it's one
of just a few rigorous experiments to show such a link between the gut
and the brain despite years of theorizing by scientists.

There's still more science to do before you should start distrusting
your food cravings, though. Along with not having a way to test the
idea in humans, the team didn't measure the importance of microbes in determining diet compared to anything else.

"It could be that what you've eaten the day before is more important
than just the microbes you have," Kohl said. "Humans have way more
going on that we ignore in our experiment. But it's an interesting idea
to think about." And it's just one behavior that microbes could be
tweaking without our knowledge. It's a young field, Kohl points out,
and there's still lots to learn.

"I'm just constantly amazed at all of the roles we're finding that
microbes play in human and animal biology," Kohl said.


========================================================================== Story Source: Materials provided by University_of_Pittsburgh. Original
written by Patrick Monahan. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Brian K. Trevelline, Kevin D. Kohl. The gut microbiome influences
host
diet selection behavior. Proceedings of the National Academy of
Sciences, 2022; 119 (17) DOI: 10.1073/pnas.2117537119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220420151540.htm

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