In an
ecosystem within us, microbes evolved to sway food choices
It sounds like science
fiction, but it seems that bacteria within us -- which outnumber our own cells
about 100-fold -- may very well be affecting both our cravings and moods to get
us to eat what they want, and often are driving us toward obesity.
In an article published in the journal BioEssays, researchers from UC San Francisco,
Arizona State University and University of New Mexico concluded from a review
of the recent scientific literature that microbes influence human eating
behavior and dietary choices to favor consumption of the particular nutrients
they grow best on, rather than simply passively living off whatever nutrients
we choose to send their way.
Bacterial species vary
in the nutrients they need. Some prefer fat, and others sugar, for instance.
But they not only vie with each other for food and to retain a niche within
their ecosystem -- our digestive tracts -- they also often have different aims
than we do when it comes to our own actions, according to senior author Athena
Aktipis, PhD, co-founder of the Center for Evolution and Cancer with the Helen
Diller Family Comprehensive Cancer Center at UCSF.
"Bacteria within
the gut are manipulative," said Carlo Maley, PhD, director of the UCSF
Center for Evolution and Cancer and corresponding author on the paper."
"There is a diversity of interests represented in the microbiome, some
aligned with our own dietary goals, and others not."
Fortunately, it's a
two-way street. We can influence the compatibility of these microscopic,
single-celled houseguests by deliberating altering what we ingest, Maley said,
with measurable changes in the microbiome within 24 hours of diet change.
"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."
There are even
specialized bacteria that digest seaweed, found in humans in Japan, where
seaweed is popular in the diet.
Research suggests that
gut bacteria may be affecting our eating decisions in part by acting through
the vagus nerve, which connects 100 million nerve cells from the digestive
tract to the base of the brain.
"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 Aktipis, who is currently in the Arizona State University Department of Psychology.
In mice, certain
strains of bacteria increase anxious behavior. In humans, one clinical trial
found that drinking a probiotic containing Lactobacillus casei improved mood in
those who were feeling the lowest.
Maley, Aktipis and
first author Joe Alcock, MD, from the Department of Emergency Medicine at the
University of New Mexico, proposed further research to test the sway microbes
hold over us. For example, would transplantation into the gut of the bacteria
requiring a nutrient from seaweed lead the human host to eat more seaweed?
The speed with which
the microbiome can change may be encouraging to those who seek to improve
health by altering microbial populations. This may be accomplished through food
and supplement choices, by ingesting specific bacterial species in the form of
probiotics, or by killing targeted species with antibiotics. Optimizing the
balance of power among bacterial species in our gut might allow us to lead less
obese and healthier lives, according to the authors.
"Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating," the authors wrote.
The authors met and
first discussed the ideas in the BioEssays paper at a summer school conference
on evolutionary medicine two years ago. Aktipis, who is an evolutionary
biologist and a psychologist, was drawn to the opportunity to investigate the
complex interaction of the different fitness interests of microbes and their
hosts and how those play out in our daily lives. Maley, a computer scientist
and evolutionary biologist, had established a career studying how tumor cells
arise from normal cells and evolve over time through natural selection within
the body as cancer progresses.
In fact, the evolution
of tumors and of bacterial communities are linked, points out Aktipis, who said
some of the bacteria that normally live within us cause stomach cancer and
perhaps other cancers.
"Targeting the
microbiome could open up possibilities for preventing a variety of disease from
obesity and diabetes to cancers of the gastro-intestinal tract. We are only
beginning to scratch the surface of the importance of the microbiome for human
health," she said.
The co-authors'
BioEssays study was funded by the National Institutes of Health, the American
Cancer Society, the Bonnie D. Addario Lung Cancer Foundation and the Institute
for Advanced Study, in Berlin.
Story Source:
The above story is
based on materials provided by University of California, San Francisco (UCSF).
The original article was written by Jeffrey Norris. Note: Materials may be edited for
content and length.
Journal
Reference:
1.
Joe Alcock, Carlo C. Maley, C. Athena Aktipis. Is eating behavior manipulated
by the gastrointestinal microbiota? Evolutionary pressures and potential
mechanisms. BioEssays,
2014; DOI: 10.1002/bies.201400071
Cite This Page:
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MLA
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APA
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Chicago
University of California,
San Francisco (UCSF). "Do gut bacteria rule our minds? In an ecosystem
within us, microbes evolved to sway food choices." Science
Daily, 15 August 2014.
<www.sciencedaily.com/releases/2014/08/140815192240.htm>.
