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 (conducted by scientists with UCLA’s Gail and Gerald Oppenheimer Family Center for Neurobiology of Stress and the Ahmanson–Lovelace Brain Mapping Center at UCLA) shows what has been suspected but until now had been proved only in animal studies: that signals travel the opposite way as well.

“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 lead author of the study. “Our study shows that the gut–brain connection is a two-way street.”

“Many of us have a container of yogurt in our refrigerator that we may eat for enjoyment, for calcium or because we think it might help our health in other ways,” Tillisch said. “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.”

In the study, published in the journal Gastroenterology. thirty-six women were divided in into three groups: one group ate a yogurt containing a mix of probiotics (Bifidobacteriumanimalis subsp Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp Lactis 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.
The researchers found that the brain effects from the probiotic food could be seen in many areas, including those involved in sensory processing and those associated with emotion.

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, that people with high-vegetable, fiber-based diets have a different composition of their microbiota, or gut environment, than people who eat the more typical Western diet that is 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.”

The UCLA researchers are seeking to pinpoint particular chemicals produced by gut bacteria that may be triggering the signals to the brain. They also plan to study whether people with gastrointestinal symptoms such as bloating, abdominal pain and altered bowel movements have improvements in their digestive symptoms which correlate with changes in brain response. Meanwhile, these findings could lead the way to creating probiotic dietary interventions that alter mood, anxiety, stress, and pain sensitivity.It's also possible that changing the composition of gut bacteria could lead to treatments for chronic pain disorders, he said, as well as symptoms of brain conditions like autism, Parkinson's, and Alzheimer's disease.

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