We often associate mental phenomena, ideas, and emotions with the brain or head. This vision can become somewhat simplistic because our body works as a whole, and each part is essential for overall performance. Numerous studies support the importance of the different body systems (beyond the brain and the nervous system) in mental and general health—the digestive system was closely linked to our psychological well-being.
The physical connection between the brain and the gut
This connection between mental states and our digestion has its physical counterpart in the vagus nerve, which links the Central Nervous System (in which the brain is included) with the digestive system. This nerve is responsible for maintaining vegetative functions such as breathing, heartbeat or digestion. But in addition to serving as a regulator of essential digestive processes, it has a crucial role as a link between cognitive and emotional states and intestinal health.
Although counterintuitive, most information flows from the digestive system to the brain, not the other way around. For example, it is widespread for digestive problems to appear when we experience stress or psychological discomfort. For example, the brain sends information to the intestine to promote proper functioning. For example, the neuronal connections of the vagus nerve send information from the intestine to the brain, highlighting the significant implication of digestive health in mental phenomena.
Recently, studies have been carried out that relate emotions such as compassion with the activation of the vagus nerve. For example, in 2010, Keltner et al. found, using neuroimaging techniques, activation of the vagus nerve in patients who were shown images of other people’s suffering. Another study by Eisenberg found that children with a higher base rate of activity in the vagus nerve were more cooperative and generous than their peers.
The “second brain.”
Surprisingly, the digestive system has about 100 million neurons that innervate it, more than those that make up the spinal cord. This set of neurons makes up the enteric nervous system, which controls the functioning of the digestive system. It would be difficult, therefore, for a system of such complexity to be solely responsible for digesting food. On the other hand, our digestive system, also called the second brain, provides a wealth of helpful information. On the other hand, both brains collaborate and influence each other. On the one hand, physical health problems generate difficulties in digestion and the structures that carry it out. But on the other hand, several factors in the digestion system fluence our mental health.
Digestive problems associated with mental health
As we mentioned before, it is expected that our stomach and digestion suffer in periods of high stress or problematic situations. Proof of this is the high incidence of digestive problems in populations with psychological disorders. For example, conditions such as depression, anxiety alexithymia or autism spectrum disorders have severe consequences for physical systems, and the digestive system is perhaps one of the most affected. The repression of emotions or poor regulation of them become problems in our digestive tract.
In the case of bipolar disorder, the relationship between digestive and mental health is especially notable. Gastroparesis, a widespread digestive syndrome in patients with this disorder, is usually treated with drugs used to treat bipolarity in non-bipolar patients. Therefore, it is becoming increasingly clear that both conditions have underlying mechanisms. In addition, gastritis or inflammation in the digestive tract, derived from the psychological stress of psychological illness, feeds back the mental response of anxiety and depression in bipolar patients.
In this way, any psychological or environmental factor that causes us pmentalychological stress will very poy have consequences on digestive health.
Digestive factors that influence mental health
Recent studies have found a relationship between the microbiota or intestinal flora and certain mental illnesses. In some of these studies, cells from the microbiota of patients with psychiatric disorders are implanted in healthy rodents, and it is observed how the latter show symptoms of the mental illness of their donor.
An essential part of some of the primary neurotransmitters is manufactured in the intestine. Neurotransmitters would be something like the “signals” with which neurons communicate with each other. Only a tiny part of the dopamine and serotonin released by neurons is made in the brain. The rest is made in other areas of the body. Serotonin, among other functions, is involved in emotional regulation, and imbalances of this substance are related to depression. For its part, dopamine, the neurotransmitter of pleasure, is secreted by stimuli such as food, drink, sex or drugs. This helps us reinforce and repeat initially adaptive responses that help us survive.
Emotions and the gut
The undeniable participation of the digestive system in the synthesis of neurotransmitters makes this system a key element in emotional response and control of stress and anxiety. The food has a psychoactive and calming effect related to releasing neurotransmitters manufactured in the intestine. Since we are little, we establish an emotional bond with food, which is the basis of problems such as food addictions or Eating Disorders. In the case of “binge eating” caused by emotional issues, these are directed toward fast-absorbing energy-rich foods. We usually binge on the so-called simple, refined carbohydrates (industrial pastries, salty snacks, processed foods), not vegetables. These types of foods are the most likely to cause a problem.
The link between food and emotions sometimes leads to an unhealthy relationship with what we eat. Factors such as low self-esteem, low tolerance for frustration, the need for immediate gratification, difficulties in dealing with conflicts, avoidance of problems, difficulty adapting, or existential voids predispose to an unhealthy relationship with food, either in its excess or its defect.