Human gut microbiota is associated with many health factors, but the differences between studies limit the exploration of their effects. The researchers used a new technology platform to correlate the relationship between 38 diseases and 51 drugs and gut microbiota. The researchers found an unprecedented association between gut flora and disease, and found the most common associations between multiple diseases and gut microbiota, and determined which diseases and drugs and gut microbiota have.

“To have your stomach knotted, butterflies in your stomach” “To put the spleen in bouillon” “To make the bile” … Well before the scientific reality gives them reason, the popular expressions put forward the link narrow between our belly and our emotions …

Today, we know that 200 million neurons are present in the intestine and that this enteric nervous system communicates closely with the central nervous system.

More recently, studies have suggested that in addition to its metabolic and immune functions, the gut microbiota would also participate in communication between the gut and the brain and influence brain function. And today, researchers are studying the possible links between an imbalance of the gut microbiota and certain psychological disorders: stress, depression but also neurodegenerative diseases (Parkinson, Alzheimer …).

What do the latest scientific studies reveal concretely? What are the hopes for prevention and long-term health?
95% of serotonin is produced in the gut and takes part in the exchange between the brain and the intestine via the vagus nerve. Serotonin is a neurotransmitter, sometimes also called “serenity hormone” that regulates a wide range of functions such as mood or behavior.

Between the brain and the intestine, a third actor slipped: the intestinal microbiota that would also take part in this mysterious dialogue.

The role of the gut microbiota in intestinal-brain communication
The intestinal microbiota corresponds to all the microorganisms that colonize the digestive tract. It is populated with more than 100,000 billion micro-organisms. It’s 10 times more than the number of cells in the body. Bacteria are widely represented, with more than 1000 species and 7000 different strains among which we find essentially the following families: Bacteroidetes and Firmicutes.

Recent research has suggested that the gut microbiota would be involved in communication between the gut and the brain and thus play a role in brain function.

The intestinal microbiota therefore influences the functions of the organism, beyond its metabolic roles and as a barrier against external aggression. His involvement in the gut-brain axis even suggests that in the event of imbalance, it could play a role in many neurological and psychiatric diseases.

What is the role of the gut microbiota on stress, anxiety or depression …?

Even if the mechanisms are not yet clearly elucidated, it is known that the gut microbiota acts on the brain, through the blood and nerve channels via the secretion and release of certain molecules.

This bowel / brain communication has led researchers to investigate the possible links between an imbalance in the gut microbiota and some frequently encountered psychic disorders, such as stress or anxiety.

First discovery: the intestinal microbiota seems to have a moderating effect on the stress response.

In axenic mice (without intestinal microbiota), research has shown hypersensitivity to stress with an increase in the blood concentration of a stress-related hormone, corticosterone, in these animals5. As a corollary, other studies have shown that the administration of probiotic bacteria to rats and mice can reduce the release of corticosterone caused by stressful situations.

Studies have also found changes in intestinal microbiota composition in rodents with depressive behavior.

In humans, the presence of dysbiosis in depressive patients was also examined. Researchers compared the composition of the gut microbiota from 37 individuals with depression to a control group of 18 individuals. An under-representation of Bacteroidetes with an over-representation of the genus Alistipes has been observed in individuals with depression.

All of this research suggests that the gut microbiota plays a role in our behavior and our emotional reactivity.

In fact, recently, a team of American researchers showed that women who ate a probiotic-enriched milk product for one month paid less attention to negative emotional stimuli, such as faces expressing fear or anxiety …

Intestinal microbiota and autism
The possible involvement of the gut microbiota in autism is also the subject of interesting research. Pilot studies have compared the microbiota of autistic children with those of control children, and reported notable differences10,11. However, the conclusions of this work are not consensual because different bacteria have been implicated according to the studies.

A possible link between intestinal microbiota and neurodegenerative diseases?
Two hypotheses of work are evoked for this type of diseases: the action of the gut microbiota on the immune system on the one hand and the brain-intestinal axis on the other hand.

Multiple sclerosis (MS)

In multiple sclerosis (MS), hypotheses to date are based on experimental studies conducted in animals only. The data are still indirect, but the intestinal microbiota could play a role in the onset or development of the disease, including its immune function.

The complete mechanisms involved are not yet clarified. Studies are ongoing in humans to investigate the existence of dysbiosis in MS.

Parkinson disease
A recent Finnish study found significant differences between the composition of people with Parkinson’s disease and a control group.