The connection that exists between the intestine and the brain is known as the “gut-brain axis”. This connection has received more and more attention among researchers in recent years and many believe that the knowledge of this connection can come to have an impact on how we treat health problems such as IBS, anxiety and depression. But how do the gut and the brain actually communicate? In this article, we describe the four main communication pathways that exist between the gut and the brain.
A large part of the communication that occurs between the intestine and the brain happens via the nervous system. The nervous system partly consists of neurons – a type of cell that is found both in the brain and in the central nervous system, which provides the body with instructions for how to act in different situations. There are about 100 billion neurons in the brain and there are 500 million neurons in the gut, which is one of the reasons why the gut is sometimes called “the second brain”.
The intestine and brain are also connected by specific nerves, the largest and most significant of which is the vagus nerve. The vagus nerve stretches from the root of the brain down to the intestinal system and signals travel through it, in both directions, that affect the function of the intestine and the brain respectively. For example, studies have shown that people with IBS and Crohn’s disease suffer from impaired activity in the vagus nerve. It has also been shown that stress prevents signals sent via the vagus nerve from arriving properly, which can lead to gastric problems.
Different types of chemicals and residual products are created in our intestines when the bacteria that live there consume fibres. These chemicals can, in turn, affect the brain. One group of these chemicals is called short-chain fatty acids or SCFA, which for example includes butyric acid. These short-chain fatty acids are very healthy and help stimulate the vagus nerve. In addition, the fatty acids can also have an appetite suppressant effect, assist in the production of certain vitamins and improve the condition of the intestinal wall.
The brain and intestine are also connected via so-called neurotransmitters. Neurotransmitters are molecules that can carry nerve signals throughout the body. These molecules and substances are produced in the brain but also, in large part, in the intestines. The intestinal bacteria produce a large part of the body’s serotonin, which is a neurotransmitter and a hormone that, among other things, regulates sleep, wakefulness and appetite, and also GABA which, among other things, is important for memory function. When these substances are produced in the intestine, they can then affect which signals are sent to the brain via the vagus nerve.
The HPA axis, also known as “the stress axis”, is a set of hormones that is produced in the brain and adrenal glands. Hormones such as cortisol and adrenaline are produced in these locations, which are hormones that are activated when we are exposed to stress. In other words, the HPA axis controls how we react to stressful situations – both everyday stressful situations, and more extreme situations. Being exposed to excessive amounts of stress for extended periods of time can have a negative effect on the body and specifically on the intestines, since the aforementioned stress hormones contribute to the weakening of the intestinal wall and also promotes inflammation in the body.
This area of research is still in its infancy and more research is needed in order to conclusively establish the significance of this connection. One thing to take note of, however, is that our state of mind is closely linked to our gut health. Stress and anxiety seem to affect our intestinal health very negatively, and if you already suffer from a physical ailment, stress could likely worsen this condition. In other words, long-term physical health is not just about diet and exercise – mental well-being also plays a significant role!