Changing Gut Bacteria with Yogurt: Diet Affects Brain Function in Women

It turns out that you really are what you eat. Researchers now have the first evidence that bacteria ingested in food can affect brain function in humans. The new findings come after a study of healthy women who ate yogurt.

In order to study how prebiotics, beneficial bacteria found in yogurt, affect women, researchers divided 36 women into three groups. One group was given a specific yogurt to eat over the course of the study. The yogurt contained a mix of several prebiotics that are thought to have a positive effect on the intestines. The second group was given a dairy product that tasted like yogurt, but had no prebiotics. The third group was given nothing at all during the course of the research.

After allowing the women to consume (or not consume) the products for four weeks, the researchers then examined their brains. They used functional magnetic resonance imaging (fMRI) scans both before and after the actual study. More specifically, they examined the women during 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 then had to match them to other faces showing the same emotions. It turns out that yogurt may have more of an impact than we thought.

"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," said Kirsten Tillisch, one of the researchers, in a news release. "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 a new meaning."

So exactly how did the yogurt affect women? Researchers found that, compared with the women who didn't consume the yogurt, those who did showed a decrease in activity in both the insula, which processes and integrates internal body sensations, like those from the gut. In addition, they saw a decrease in activity in the somatosensory cortex during the emotional reactivity task.

That's not all that they found. Women who ate the yogurt also 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, in contrast, showed stable or increased activity in this network.

"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," said Emeran Mayer, the study's senior author, in a news release. "Now we know that this has an effect not only on the metabolism but also affects brain function."

Currently, the researchers are examining the potential benefits of certain prebiotics in yogurts on mood symptoms, such as anxiety. The findings could eventually lead the way to healthier diets, or drugs that could build upon the health benefits of certain foods.

The findings are published in the journal Gastroenterology.