Gut bacteria through diet affects brain function
- July 8, 2013
- Sophie Langley
Regular consumption through yoghurt of beneficial bacteria, known as probiotics, alters brain function, according to an early proof-of-concept study from the University of California Los Angeles (UCLA).
The study, conducted by scientists at UCLA and published in the June online edition of the journal Gastroenterology, found that changing the bacterial environment, or microbiota, in the gut changed the areas of the brain that were active, both while in a resting state and in response to an emotion-recognition task.
Scientists have known that the brain sends signals to the gut, which is why stress and other emotions can contribute to gastrointestinal problems. The UCLA researchers said this study showed that the signals also travel in the opposite direction, from gut to brain.
“Time and time again we hear from patients that they never felt depressed or anxious until they started experiencing problems with their gut,” said Dr Kirsten Tillisch, an Associate Professor of Medicine at UCLA’s David Geffen School of Medicine and lead author of the study. “Our study shos that the gut-brain connection is a two-way street,” she said.
“Our findings indicate that some of the contents of yoghurt 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,” Dr Tillisch said.
The small study involved 36 women between the ages of 18 and 55. Researchers divided the women into three groups: one group ate a specific yoghurt containing a mix of several probiotics – bacteria thought to have a positive effect on the intestines – twice a day for four weeks; another group consumed a dairy product that looked and tasted like the yoghurt but contained no probiotics; and a third group ate no product at all.
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. Researchers said this task, designed to measure the engagement of affective and cognitive brain regions in response to a visual stimulus, was chosen because previous research in animals had linked changes in gut flora to changes in affective behaviors.
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, like those form the gut — and the somatosensory cortex during the emotional reactivity task.
Further, in response to the task, these women had a decrease in the engagement of a widespread network in the brain that includes emotion-, cognition- and sensory-related areas. The women in the other two groups showed a stable or increased activity in this network.
During the resting brain scan, 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 researchers said they were surprised to find that the brain effects could be seen in many areas, including those involved in sensory processing and not merely those associated with emotion.
Implications for future research
Authors of the UCLA study said that knowledge that signals are sent from the intestine to the brain and that they can be modulated by 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”.
The researchers said future studies may have implications for the use of repeated courses of antibiotic treatments, and for treatment of chronic pain and brain-related diseases.
The study was funded by the research arm of global dairy company Danone. One of the study’s senior authors has served on the company’s scientific advisory board. Three of the study authors are employed by Danone Research and were involved in the planning and execution of the study (providing the products) but researchers said these authors had no role in the analysis or interpretation of the results.
Probiotic health claims
Meanwhile, the health benefits of probiotic and fermented food has been a controversial topic in Europe. In March 2013, Australian Food News reported that the European Commission was expected to allow use of the term ‘probiotic’ as a ‘general descriptor’ after it was banned as a health claim in December 2012.