Is there a link between the microbiota and stress, mood?
Physiologically, the cells of the intestinal wall, directly linked to the microbiota, secrete the same neurotransmitters as brain cells, primarily serotonin, dopamine, and norepinephrine. These neurotransmitters act on the central nervous system and regulate mood and emotions.
Serotonin also promotes the secretion of melatonin—the sleep hormone—and therefore plays a crucial role in our sleep. The quality of the gut microbiota, its diversity, and its balance influence a series of chemical reactions that affect the proper secretion of intestinal neurotransmitters. After having long considered the gut to be the second brain, it is now recognized as the first brain, the one that secretes the greatest quantity and quality of neurotransmitters; neurotransmitters that regulate emotional balance. We know that the quality and diversity of the microorganisms that make up the microbiota have a beneficial influence on the functioning of intestinal cells, hence the link between the microbiota and emotional balance.
The microbiota therefore plays a crucial role in managing stress and mood (sociability, anxiety, depression).
The reverse is also true: stress affects the gut and the composition of our microbiota by activating nerve and hormonal pathways, which function bidirectionally. The vagus nerve is even composed of 90% ascending fibers, meaning they carry messages from the gut to the brain. We now know that the vagus nerve transmits a variety of information, ranging from nutrient content to the presence of bacterial products. The brain regions that receive this information are located in the brainstem and the hypothalamus, and are directly involved in the stress response.
Some researchers go further and demonstrate the involvement of the microbiota in depression and autism.
Researchers from the Pasteur Institute, Inserm, and the CNRS conducted a study showing that an imbalance in the gut microbiota can cause a collapse of certain metabolites (small organic compounds produced by metabolism), which are responsible for depressive states. This study also demonstrates a link between the gut microbiota and the effectiveness of fluoxetine, a molecule frequently used as an antidepressant (the active ingredient in Prozac). Given current knowledge, the term "gut-microbiota-brain axis" seems more appropriate.
For several years, research on autism has identified its genetic origin, but has also revealed links with the digestive system, and more specifically the gut microbiota. Recent observations and experiments confirm that the majority of autistic children exhibit gut microbiota imbalances, or dysbiosis. Transferring microbiota from autistic children to sterile mice (without gut flora) induces the symptoms of the disorder in these mice.
According to a 2018 study by American researchers, treatment with Lactobacillus reuteri—a species of gut bacteria found in yogurt and breast milk—improves social interactions in three mouse models. However, at this stage of their work, these researchers do not recommend the use of over-the-counter L. reuteri supplements to treat autism, as they do not know if all strains are effective or what dosage should be used for affected individuals.
Why are gut bacteria good for our mood?
Gut bacteria secrete fatty acids, vitamins including vitamin B and micronutrients necessary to produce neurotransmitters.
Two gut bacteria are particularly beneficial to our mood: lactobacillus and bifidobacterium. These bacteria produce GABA molecules, an amino acid that modulates the activity of the central nervous system and therefore promotes an improvement in our nervous state.
What diet should we adopt to maintain the microbiota-gut-brain axis?
To reduce stress we need a low-inflammation intestinal environment and therefore a balanced and varied diet.
In this area, our number one enemy is sugar: it inflames the intestinal lining, damages the intestinal wall, increasing the passage of intestinal toxins from the gut into the bloodstream, and alters the digestive mucous membranes, leading to intestinal hyperpermeability. It promotes the proliferation of Candida yeasts, which destroy beneficial bacteria, triggering flatulence and even vaginal yeast infections. It's a never-ending downward spiral because sugar also depletes our reserves of magnesium and B vitamins, which are essential for vitality and mood regulation.
Sugar is everywhere, in sodas of course, alcohol, but also in all industrial products (tomato sauces, prepared meals, pastries…), in the traditional baguette: one tradition contains the equivalent of 13 sugar cubes!
Our best friends are foods rich in fiber, vitamins, trace elements, and fatty acids. Therefore, favor whole grains, eggs, white meats, fish, legumes, seasonal and organic fruits and vegetables, and fermented foods. Researchers have shown that the higher the fiber intake, the greater the diversity and number of bacterial species. This is a way to consume natural probiotics. The gut microbiota is all the more stable and balanced. Furthermore, the breakdown of fiber produces short-chain fatty acids that have protective effects on our health. In the gut, these molecules help, among other things, to regulate inflammatory processes. They stimulate the production of glucose by the intestine, which creates a feeling of satiety.
Nourishing our microbiota with dietary supplements helps to regulate stress and mood.
Whether used as a course for a boosting effect or as a long-term aid, probiotic capsules such as "Microbiota and Skin," composed of four probiotic strains that have a targeted action on digestion and transit, are a valuable aid for maintaining the balance of the microbiota and regulating stress and mood.
