The intestinal flora affects our thoughts and emotions, a study has found. The composition of the flora is reflected in the volume of brain areas involved in the treatment of complex information and memory, and also influences human behavior.

It has been discovered in a study that intestinal flora affects not only our physical health, but also our thoughts and emotions. The flora or intestinal microbiota is integrated by the set of bacteria that live in the intestine, most of them playing a beneficial role for health, as they help the absorption of nutrients and are essential for the synthesis of certain compounds, such as vitamin K and others of the B complex.

It is estimated that the human being has about 2,000 different bacterial species, of which only 100 can become harmful. The flora groups all the bacteria of the gastro-intestinal system and constitutes the largest microbiota reserve of the entire human organism.

This research has identified relationships between two types of flora and their incidence on some emotional responses in humans. According to the authors of this study, it is the first empirical demonstration of the relationship between different human behaviors and the microbial composition of healthy human beings.

How was this relationship demonstrated?

This research has shown that the same association affects humans. The scientists analyzed faecal samples from 40 healthy women, aged between 18 and 55 years, and divided the results of the analyzes into two groups, depending on the composition of their intestinal flora.

One of the groups analyzed showed a greater abundance of one type of bacteria called Bacteroides, while the other group had a greater abundance of another bacteria called Prevotella. Next, the researchers scanned the participants’ brains through magnetic resonance imaging, while showing them various images designed to provoke an emotional reaction, whether positive, negative or neutral.

In this way they were able to discover that the people who had an intestinal flora dominated by Bacteroides had a denser gray matter in the frontal cortex and the insular regions, the areas of the brain specialized in the treatment of complex information. They also showed a more bulky hippocampus, the brain area involved in memory.

However, the people in the second group had less developed those same brain areas, confirming that there is a close relationship between the emotional, sensory and attention regions that we have in the brain, and the composition of the intestinal flora. When the researchers showed negative images, the participants who had more Pretovella bacteria showed poorer activity in the hippocampus region, at the same time they had higher levels of anxiety, stress and irritability when they looked at the images.

What is the risk factor?

According to the researchers, since the hippocampus helps regulate emotions, when the brain has a smaller hippocampus, linked to the composition of the intestinal flora, negative images can provoke more intense emotional reactions.

“A hippocampus less involved in negative images may be associated with a disproportionate emotional reaction,” the authors write in their article in Psychosomatic Medicine: Journal of Behavioral Medicine. According to the researchers, these emotional changes imply a characteristic deficit of certain mental disorders such as depression, post-traumatic stress syndrome and personality disorders.

Although the people participating in this study were healthy, these results indicate that the profiles obtained from the structure of the intestinal flora constitute a factor of vulnerability for these people, in the face of possible psychiatric disorders. The researchers point out that these results should not be considered conclusive, since the sample analyzed is small. Therefore, they propose to carry out this study with many more people in order to better understand the relationship, already outlined, between the intestinal flora, emotions and human behavior.

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