Intestine: Why do we say that it is our second brain?

Did you know that the function of our digestive system goes beyond simply digesting food? The human intestine is colonized by an infinite number of bacteria and fungi. The whole of these is what is known as “intestinal microbiota”, with important digestive, immunomodulatory, nervous and protective functions. Some microorganisms are beneficial, but the excessive growth of others can have a negative impact on our health.

Research in recent years has focused on the effects of each person’s microbiota on their metabolism, their ability to gain or lose weight, heart disease or dermatology, and even on multiple neurological diseases such as depression, Parkinson’s disease or autism. This is due to the fact that our intestine produces a lot of substances related to our immunity, satiety and even our mood.

The intestine and the brain are closely connected by the vagus nerve in a “bidirectional” way, that is, the brain influences the diversity of our bacteria and these influence our emotions. For example, 95% of serotonin (the so-called “welfare hormone”) is produced in the gut and regulates multiple brain functions such as mood or behavior. Imagine if we do not have the bacteria that participate in the synthesis of serotonin…could this be one of the reasons why we are more depressed or exhausted? 

Therefore, how our intestines work can lead to problems such as depression and anxiety. It is believed that this gut-brain connection is responsible for the fact that our mood influences our intestinal transit so much. Many people with depression or anxiety develop digestive symptoms such as diarrhea, constipation, abdominal swelling. But, what if the origin of the problem was at the intestinal level? What if our intestinal health had an effect on our mood and that’s why we don’t understand why we feel this way?

The intestinal microbiota completes its diversity over the first year of life and is considered more or less stable during the 3-5 years, varying according to each person’s diet and lifestyle. Each individual has a unique and unrepeatable microbiota.

To achieve a good intestinal function and correct absorption of nutrients by food, it is essential that the different microbial genera we have in the intestine are in a certain quantity, proportion and balance. This will be achieved by eating a varied and healthy diet as possible, as well as regular physical exercise, consumption of adequate probiotics, rest, maintaining social relations and taking care of sleeping hours.

Each microbial genus has a function, so both its deficit and its excess can alter its stability and hinder the proper functioning of the digestive system. This is known as “dysbiosis”.

When this imbalance between good and bad bacteria is altered (due to situations of stress, chronic use of medicines and especially antibiotics, a bad diet full of sugar and ultraprocessed, a sedentary life, tobacco or alcohol…) chronic diseases can be caused.

The studies of intestinal dysbiosis can open a door to detect the origin of diverse intestinal pathologies, like bad digestions, flatulences, constant diarrheas, intolerances, constipation… and even nonintestinal pathologies like migraines, atopic dermatitis, acne, candidiasis, allergies, rheumatism or fibromyalgia. Once the origin of the problem has been detected and the bacterial groups altered, a specific probiotic therapy and personalized nutrition is started for each patient together with a change in lifestyle.

Acid-lactic bacterial species of the genera Lactobacillus and Bifidobacterium are commonly used to stabilize the intestinal environment. 

There is also long clinical experience with other types of probiotic microorganisms with more powerful action on the immune system such as Enterococcus faecalis and Eschericha coli.

In parallel, the consumption of prebiotics (non-digestible components of the diet, mainly resistant starch and other types of fiber) metabolized by the intestinal microbiota, promote the growth of one or more bacterial species, thus modifying the composition of the microbiota and/or its metabolic performance.


We are, therefore, facing a new world in which we relate the origin of multiple pathologies with alterations of microorganisms that are part of us. There is still much to discover, but at the same time it is a super promising line of research with important advances for our long-term health and totally personalized treatments