By Will Parker
In a discovery that carries significant implications for changing brain
function through dietary interventions, UCLA researchers say they now
have the first evidence that bacteria ingested in food can affect how
the human brain works. The study, which focused on women who consumed
yogurt containing the bacteria known as probiotics, appears in the
journal Gastroenterology.
Researchers have long known that the brain sends signals to the gut,
which is why stress and other emotions can contribute to
gastrointestinal symptoms. This new study claims to show that signals
travel the opposite way as well. "Our findings indicate that some of the
contents of yogurt may actually change the way our brain responds to
the environment. When we consider the implications of this work, the old
sayings 'you are what you eat' and 'gut feelings' take on new meaning,"
said Dr. Kirsten Tillisch, lead author of the study.
The study involved 36 women between the ages of 18 and 55 who were
divided into three groups: one group ate a specific yogurt containing a
mix of several probiotics twice a day for four weeks; another group
consumed a dairy product that looked and tasted like the yogurt but
contained no probiotics; and a third group ate no product at all.
MRI scans conducted both before and after the four-week study period
looked at the women's brains in a state of rest and in response to an
emotion-recognition task in which they viewed a series of pictures of
people with angry or frightened faces and matched them to other faces
showing the same emotions. This task was used to measure the engagement
of affective and cognitive brain regions in response to a visual
stimulus.
The researchers found that the women who consumed the probiotic yogurt
showed a decrease in activity in both the insula - which processes and
integrates internal body sensations, like those from the gut - and the
somatosensory cortex during the emotional reactivity task.
Tillisch said she was surprised to find that these effects could also
be seen in other sensory- and cognition-related brain areas. The women
in the other two non-probiotic groups showed stable or increased
activity in these networks.
During the resting brain scan part of the experiment, the women
consuming probiotics showed greater connectivity between a key brainstem
region known as the periaqueductal grey and cognition-associated areas
of the prefrontal cortex. The women who ate no product at all, on the
other hand, showed greater connectivity of the periaqueductal grey to
emotion- and sensation-related regions, while the group consuming the
non-probiotic dairy product showed results in between.
The knowledge that signals are sent from the intestine to the brain and
that they can be modulated by a dietary change is likely to lead to an
expansion of research aimed at finding new strategies to prevent or
treat digestive, mental, and neurological disorders.
By demonstrating the brain effects of probiotics, the study also raises
the question of whether repeated courses of antibiotics can affect the
brain, as some have speculated. Antibiotics are used extensively in
neonatal intensive care units and in childhood respiratory tract
infections, and such suppression of the normal microbiota may have
long-term consequences on brain development.
"Time and time again, we hear from patients that they never felt
depressed or anxious until they started experiencing problems with their
gut," Tillisch said. "Our study shows that the gut-brain connection is a
two-way street."
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