How Are the Gut and Brain Connected?

The gut-brain axis is a term for the communication network that connects your gut and brain (1Trusted Source, 2Trusted Source, 3Trusted Source).

These two organs are connected both physically and biochemically in a number of different ways.

The Vagus Nerve and the Nervous System

Neurons are cells found in your brain and central nervous system that tell your body how to behave. There are approximately 100 billion neurons in the human brain.

Interestingly, your gut contains 500 million neurons, which are connected to your brain through nerves in your nervous system (5Trusted Source).

The vagus nerve is one of the biggest nerves connecting your gut and brain. It sends signals in both directions (6Trusted Source, 7Trusted Source).

For example, in animal studies, stress inhibits the signals sent through the vagus nerve and also causes gastrointestinal problems (8Trusted Source).

Similarly, one study in humans found that people with irritable bowel syndrome (IBS) or Crohn’s disease had reduced vagal tone, indicating a reduced function of the vagus nerve (9Trusted Source).

An interesting study in mice found that feeding them a probiotic reduced the amount of stress hormone in their blood. However, when their vagus nerve was cut, the probiotic had no effect (10Trusted Source).

This suggests that the vagus nerve is important in the gut-brain axis and its role in stress.

Neurotransmitters

Your gut and brain are also connected through chemicals called neurotransmitters.

Neurotransmitters produced in the brain control feelings and emotions.

For example, the neurotransmitter serotonin contributes to feelings of happiness and also helps control your body clock (11Trusted Source).

Interestingly, many of these neurotransmitters are also produced by your gut cells and the trillions of microbes living there. A large proportion of serotonin is produced in the gut (12Trusted Source).

Your gut microbes also produce a neurotransmitter called gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety (13Trusted Source).