(FACT CHECK) The digestive system is the second brain, is that true?

Why is the Digestive System Called the Second Brain?

Along the digestive tract there is a very large network of nerves called the enteric nervous system (ENS). This system consists of approx 500 million neuronsa much larger amount than most other body organs. These neurons are spread from the esophagus to the large intestine. They are responsible for regulating various digestive activities, such as moving the intestinal muscles so that food is pushed through, regulating the release of digestive enzymes, controlling the absorption of nutrients, monitoring blood flow to the digestive tract, and helping to coordinate the defecation process.

Interestingly, the ENS is able to carry out most of these tasks without having to wait for direct commands from the brain. It is because of this unique level of independence that scientists have dubbed the enteric nervous system the “second brain.”

However, it should be emphasized that this term is just a scientific analogy, it does not mean that there is an actual second brain in the stomach (except in the case of autopsied corpses, the brain is removed from the head and stored in the abdominal cavity so that it does not seep out of the incision in the head ).

How is it different from the real brain?

The human brain is the control center of the entire body. In it there are billions of neurons that work together to carry out various high-level functions, such as thinking logically, remembering experiences, learning new things, making decisions, speaking, recognizing faces, fostering creativity, controlling consciousness, and regulating complex emotions.

In contrast, the enteric nervous system has a much more specific function, namely regulating the activity of the digestive tract. The neurons in the intestine are indeed able to “communicate”, but this communication focuses on questions such as whether the food has reached the intestines, whether digestive enzymes need to be released, whether the intestinal muscles need to contract, and whether there are harmful substances that need to be excreted. In other words, the ENS is a local control system for digestion, not the center of the human mind.

Why Can Mentality Affect the Stomach?

Almost everyone has experienced the following conditions, for example feeling depressed and having a stomach ache, stress resulting in loss of appetite, anxiety and then experiencing diarrhea, or sadness resulting in stomach discomfort.

This phenomenon is not just a mental problem. The brain and digestive tract are connected by a communication network known as gut-brain axisor the axis between the gut and the brain. Through this pathway, the brain sends signals to the digestive system via nerves, hormones and various immune molecules.

When a person experiences stress, the brain increases the release of stress hormones such as cortisol. This condition can change bowel movements, stomach acid production, and the sensitivity of the digestive tract. As a result, various complaints arise such as nausea, stomach pain, bloating, or diarrhea. This is the reason why psychological conditions often have a direct impact on digestive health.

The relationship turns out to be two-way

What’s even more interesting is that communication goes both ways. Not only does the brain influence the gut, but the gut also sends various information back to the brain. For example, when there is intestinal inflammation, changes in the composition of intestinal bacteria, gastrointestinal infections, or impaired nutrient absorption. This condition can affect mood, energy levels, and even increase the risk of symptoms of depression or anxiety in some people.

Therefore, gut health and mental health are interrelated. However, this relationship does not mean that the intestines replace brain function.

What is the Role of the Gut Microbiota?

In the digestive tract live trillions of microorganisms called gut microbiota. Most of these are good bacteria that help digest dietary fiber, produce certain vitamins (for example vitamin K), maintain the immune system, protect the intestines from harmful bacteria, and produce various compounds that can affect nerve function.

Research in recent decades has shown that the microbiota also plays a role in communication between the gut and the brain. For example, changes in the composition of gut bacteria are known to influence the production of various chemicals which ultimately influence brain function indirectly. However, research in this area is still developing so there are still many things that are not fully understood.

Is it true that most serotonin is produced in the intestines?

One frequently cited fact is that approximately 90% of the body’s serotonin is produced in the digestive tract. This statement is true, but often misinterpreted.

Serotonin produced in the intestine is mostly used to regulate bowel movements, gastrointestinal muscle contractions, and other digestive processes. The serotonin does not directly enter the brain, because there is a natural barrier called blood-brain barrier. The brain produces its own serotonin according to its needs. This means that although gut serotonin is very important for bodily health, its existence does not mean that the gut controls the entire human mind.

Why Can’t the Gut Be Called the Real Brain?

This is the most important point that is often forgotten. The enteric nervous system is incredibly complex, but the intestinal nervous system has no cognitive abilities. The gut cannot think, plan, calculate, recognize patterns, remember childhood experiences, understand language or tone, make moral decisions, or create creativity. All these functions remain under the control of the brain and central nervous system.

Therefore, the term second brain should be understood as a scientific term describing the complexity of the intestinal nervous system, not as the fact that humans actually have two brains.

How to Maintain a Healthy Relationship Between the Brain and Digestion

Because the relationship between the two is so close, maintaining intestinal health also means helping maintain overall body health. Some habits that can be done include:

1) Eat foods high in fiber from vegetables, fruit, nuts and seeds
2) Consume balanced nutritious food
3) Get enough sleep every day
4) Exercise regularly
5) Manage stress well
6) Limit consumption of fast food
7) Avoid using antibiotics without the advice of a health professional because they can disrupt the balance of the intestinal microbiota

These habits not only benefit digestion, but also support brain health, the immune system and the body’s metabolism.

CLOSURE

Scientific advances have shown that the relationship between the brain and the digestive system is much more complex than previously imagined. The enteric nervous system has millions of neurons that work independently to regulate digestive processes and communicates continuously with the brain via the gut-brain axis.

It is because of this complexity that the term “second brain” emerged. However, the term should not be taken literally. The digestive system is indeed able to influence mood and receive influences from a person’s psychological condition, but digestion does not have the ability to think, remember, learn, or make decisions like the human brain.

In short, the gut is not a second brain in the true sense, but a very sophisticated nervous system that has close communication with the brain. Understanding this difference is important so that we can enjoy the development of science without being trapped in misleading simplifications. In the end, the brain and intestines are not two organs that replace each other, but two systems that work together to keep the body healthy.

SOURCE

Furness, J. B. (2012). The Enteric Nervous System. Wiley-Blackwell.

Mayer, E. A. (2016). The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health. Harper Wave.

Mayer, E. A. (2011). Gut feelings: The emerging biology of gut-brain communication. Nature Reviews Neuroscience, 12(8)453-466.

National Institute of Diabetes and Digestive and Kidney Diseases. (2023). Your digestive system & how it works.

National Institute of Mental Health. (2024). Caring for your mental health.

Spiller, R., & Major, G. (2016). IBS and the gut-brain axis. F1000Research, 5F1000 Faculty Rev-2795.

Yoo, B. B., & Mazmanian, S. K. (2017). The enteric network: Interactions between the immune and nervous systems of the gut. Immunity, 46(6)910-926.