Studying the ‘gut-brain axis,’ UNC researchers find
evidence of an association between the gut
microbiota and the eating disorder. Researchers at
the UNC School of Medicine found that people with
anorexia nervosa have very different microbial
communities residing inside their guts compared to
healthy individuals and that this bacterial
imbalance is associated with some of the
psychological symptoms related to the eating
disorder.
The findings, published today in the journal
Psychosomatic Medicine, provide more evidence that
the abundance and diversity of the gut microbiota –
the trillions of bacteria that affect digestive
health and immunity – could also affect the
so-called “gut-brain axis.” This research suggests
that gut bacteria could play a prominent role in the
debilitating symptoms of anorexia nervosa, a serious
eating disorder that affects more than 3 million
Americans and has the highest mortality rate of any
psychological disorder.
“Other studies have linked gut bacteria to weight
regulation and behavior,” said Ian Carroll, PhD,
senior author of the paper and assistant professor
of medicine in the UNC Center for Gastrointestinal
Biology and Disease. “Since people with anorexia
nervosa exhibit extreme weight dysregulation, we
decided to study this relationship further.”
Carroll added, “We’re not able to say a gut
bacterial imbalance causes the symptoms of anorexia
nervosa, including associated symptoms, such as
anxiety and depression. But the severe limitation of
nutritional intake at the center of anorexia nervosa
could change the composition of the gut microbial
community. These changes could contribute to the
anxiety, depression, and further weight loss of
people with the disorder. It’s a vicious cycle, and
we want to see if we can help patients avoid or
reverse that phenomenon. We want to know if altering
their gut microbiota could help them with weight
maintenance and mood stabilization over time.”
For this study, Carroll’s team collected fecal
samples from 16 women with anorexia nervosa after
they were first admitted into the UNC Center of
Excellence for Eating Disorders and then again after
their weight was restored – when they were
discharged from UNC. Then Susan Kleiman, a graduate
student in Carroll’s lab and first author of the
paper, characterized the composition and diversity
of the gut microbiota in each sample.
Kleiman found significant changes in the gut
bacteria populations between admission and
discharge. The samples taken at clinic admission had
fewer different types of bacteria, making the
intestinal communities much less diverse. Microbial
diversity is a sign of better overall health. Upon
hospital discharge, the microbial diversity had
increased, but was still significantly less diverse
than that of 12 healthy individuals, whose gut
microbiotas were analyzed for this study.
As the microbial communities in patients with
anorexia improved during clinical care and weight
gain, the moods of patients also improved. Thus, the
researchers noted an association between the gut
microbiota and a central symptom of people with
anorexia nervosa.
The question remains whether improving microbial
abundance and diversity could help relieve symptoms
related to the eating disorder. To find out, Carroll
formed a team of researchers including Cynthia Bulik,
PhD, director of the UNC Center of Excellence for
Eating Disorders; John Cryan, PhD, professor at
University College Cork; Lisa Tarantino, PhD,
assistant professor of psychiatry at UNC-Chapel
Hill; Anthony Fodor, PhD, a bioinformatics expert at
UNC-Charlotte, and Hunna Watson, PhD, a psychologist
and biostatistician at UNC-Chapel Hill.
This month, they received a five-year, $2.5-million
grant from the National Institutes of Mental Health
to further study the relationship between the gut
microbiota and anorexia nervosa.
“Over the past 10 years, prominent researchers have
learned that when you take gut microbial communities
of an obese person and put it in germ-free mice --
which are maintained in sterile conditions and lack
intestinal microbiota - the mice gain more weight
than germ-free mice that have been colonized with a
gut microbiota from a lean individual,” Carroll
said. “This suggests that gut microbes mediate
weight gain or loss.”
Other animal studies showed that adding gut bacteria
to previously germ-free mice altered their behavior,
especially in relation to anxiety and stress.
“We’re not saying that altering gut bacteria will be
the magic bullet for people with anorexia nervosa,”
Carroll said. “Other important factors are at play,
obviously. But the gut microbiota is clearly
important for a variety of health and brain-related
issues in humans. And it could be important for
people with anorexia nervosa.”
As part of the new NIH grant, his team will
characterize the microbiotas of a large number of
people with anorexia nervosa as they enter UNC’s
clinic and when they are discharged, which typically
happens when they reach about 85 percent of their
ideal body weight. Then his team will put those gut
bacteria in germ-free mice. This will help Carroll
learn how the microbiota from anorexia nervosa
patients affects the biology and behavior of the
mice.
If Carroll’s team learns that the bacteria has a
detrimental effect on the mice, then this might
suggest that cultivating a healthy microbiota could
serve as a therapeutic route to help people with
anorexia nervosa.
“Currently available treatments for anorexia nervosa
are suboptimal,” Bulik said. “In addition, the
process of weight gain and renourishment can be
extremely uncomfortable for patients. Often,
patients are discharged from the hospital, and
within months and sometimes weeks they find
themselves losing weight again and facing
readmission. If specific alterations in their
microbiota could make renourishment less
uncomfortable, help patients regulate their weight,
and positively affect behavior, then we might see
fewer readmissions and more cures.”
For more information
Psychosomatic Medicine
The Intestinal Microbiota in Acute Anorexia Nervosa
and During Renourishment: Relationship to
Depression, Anxiety, and Eating Disorder
Psychopathology
Link...
University of North Carolina School of Medicine
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