UCLA researchers now have the first evidence that bacteria ingested in food can affect brain function in humans.
In an early proof-of-concept study of healthy women, they found that women who regularly consumed beneficial bacteria known as probiotics through yogurt showed altered brain function, both while in a resting state and in response to an emotion-recognition task.
Researchers have known that the brain sends signals to the gut, which is why stress and other emotions can contribute to gastrointestinal symptoms. This study shows what has been suspected but until now had been proved only in animal studies: that signals travel the opposite way as well.
Functional magnetic resonance imaging (fMRI) 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.
The researchers found that, compared with the women who didn’t consume the probiotic yogurt, those who did showed a decrease in activity in both the insula, which processes and integrates internal body sensations (from the gut) and the somatosensory cortex during the emotional reactivity task.
Essentially this means they would be less prone to anxiety or emotional upset.
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, said Dr. Emeran Mayer, a professor of medicine, physiology and psychiatry at the David Geffen School of Medicine at UCLA and the study’s senior author.
“There are studies showing that what we eat can alter the composition and products of the gut flora. In particular, people with high-vegetable, fibre-based diets have a different composition of their microbiota, or gut environment, than people who eat the more typical Western diet high in fat and carbohydrates,” Mayer said. “Now we know that this has an effect not only on the metabolism but also affects brain function.”
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 longterm consequences on brain development.
The study appears in the June edition of the peer-reviewed journal Gastroenterology.