Gut bacteria also "talk" to the brain

Did you know that your gut and your brain are in constant conversation? This is not a metaphor: there is growing scientific evidence that the gut microbiota - that invisible ecosystem of trillions of bacteria - influences our mood and the onset of mental disorders.

In 2016 an experiment with mice showed that transplanting the microbiota of people with depression could induce similar symptoms in the animals. Ignacio López-Goñi, Full Professor of Microbiology and director of the Unit for Scientific Culture and Innovation at the University of Navarra (UCC+I UNAV) discusses this in detail in his new book Microbiota and Mental Health.The connection between gut bacteria and the brain.

In this interview, financial aid us to understand to what extent this link (gut-brain bacteria) could transform the way we understand mental health. Understanding how this "forgotten organ" can condition our emotions could open the door to new therapies of the future.

What does this experiment with mice tell us about the relationship between microbiota and depression?

In a 2016 study, microbiota-free mice received microbiota transplants from people with depression and began to show similar symptoms: anxiety and loss of interest. It's as if we were able to transplant depression just by transplanting gut microbes.

Other experiments have shown that chronic treatment with broad-spectrum antibiotics in mice decreases microbial richness and diversity and generates anxiety and depressive behaviors, which are reversed by restoring the microbiota.

These examples show that there is a correlation between anxiety, stress and depression and the gut microbiota, what we know as the gut-microbiota-brain axis.

What evidence already exists in humans: correlations or causation?

We know that a dysbiosis (an alteration in the issue and diversity of the microbiota) is correlated with more than 300 diseases, from metabolic and nutritional diseases such as obesity, diabetes, chronic intestinal disorders, allergies and autoimmune and inflammatory diseases to neurological diseases such as depression, autism, Alzheimer's or Parkinson's. The great unknown is that in most cases we do not know if they are cause or consequence. The great unknown is that in most cases we do not know whether they are cause or consequence: is it the dysbiosis that causes the disease or is it the disease that generates the dysbiosis? 

What role do per diem expenses and lifestyle play in the state of our microbiota?

Modifying an adult's microbiota in a concrete and targeted way is more difficult than we thought, but the most effective way is through food. What we eat, and how we eat it, directly influences the composition and diversity of our microbiota.

Western-style per diem expenses , rich in ultra-processed foods, fats and sugars, have been shown to reduce bacterial diversity and increase pro-inflammatory bacteria, increasing the risk of anxiety and depression.

On the contrary, a per diem expenses rich in fiber, probiotics and polyphenols (which gives the fruit its color) increases the abundance of Bifidobacterium and Lactobacillus, reduces Escherichia coli and other pro-inflammatory bacteria. This favors the production of short-chain fatty acids and decreases inflammation. It is the basis of a Mediterranean per diem expenses diet that has also been shown to reduce anxiety and depression.

Therefore, the best way to have a rich and diverse microbiota, which is synonymous with a healthy microbiota, is a per diem expenses rich in fiber from fruits, vegetables, legumes, whole grains, which increases production of butyrate, polyphenols from fruits and olive oil, which favor beneficial bacteria and natural probiotics from fermented foods that provide new microorganisms. This together with a reduction of ultra-processed foods, sugars, excess salt and saturated fats that alter the microbiota and promote inflammation.

In the final, the Mediterraneanper diem expenses stands out as the most beneficial for the microbiota and the brain. But it is not only the subject of food that has an influence, but also the way it is cooked. The same food boiled or fried has different effects on our microbiota. The Mediterranean per diem expenses is a lifestyle. 

Can we improve mental health by taking probiotics or changing our diet?

If it were that easy, we'd all be happy. Drinking a yogurt won't get rid of depression. Mental health depends on many factors: genetics, environment, life experiences, chance... and microbiota.

A healthy diet that favors a numerous and diverse microbiota should be part of a healthy lifestyle that combines nutrition, exercise, less stress and no toxins (tobacco, alcohol...).

What are the risks in the fad of selling products "for the microbiota"?

Probiotics, prebiotics, postbiotics, symbiotics, psychobiotics... a whole world of products to improve our microbiota. There are hundreds, thousands programs of study, some that contradict each other.

At this point, what is the conclusion? The results SUGGEST that these products MAY MAY HAVE SOME effect on SOME people. Whether they work or not depends on the subject products and your own microbiota.

At the moment, there is only clinical evidence that probiotics are beneficial in shortening infectious diarrhea in children, in necrotizing enterocolitis and in diarrhea after heavy antibiotic treatment.

Imagine a psychiatry of the future personalized according to the bacteria of each patient?

Nowadays it seems that everything is related to the microbiota, and we might think that we are in the golden age of the microbiota, but in reality we are in the stone age.

We still need many more clinical trials with well-defined and agreed protocols, with a larger issue of patients; and we need to finish understanding the mechanisms and specific molecules that explain the relationship between the microbiota and our health.

It will then be possible to propose specific therapies based on the microbiota for certain people and certain diseases. Depending on your microbiota, your Genetics and metabolism and the disease you have, they will be able to customize a cocktail of bacteria, viruses, yeasts and specific prebiotics.

In the future, the microbiota will be part of personalized medicine.