The communication system between your gut and brain is called the gut-brain axis. They’re connected both physically and biochemically in a number of different ways. They may even influence each other’s health.

How are the gut and brain connected?

The gut-brain axis is a term for the communication network that connects your gut and brain.

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

Neurons are cells found in your brain and central nervous system that tell your body how to behave. There are approximately 86 billion neurons in the human brain.

Interestingly, your gut contains around 168 million neuronsTrusted Source, which are connected to your brain through your nervous system.

The vagus nerve is one of the biggest nerves connecting your gut and brain. It sends signals in both directionsTrusted Source.

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

Neurotransmitters are produced in the brain and the gut to control functions of both the nervous system and gastrointestinal system. The enterochromaffin cellsTrusted Source of the small intenstine (part of your gut) produce the highest concentration of serotonin.

SerotoninTrusted Source is involved in bowel function, nausea, appetite, mood, learning, memory, and sleep.

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

The trillions of microbes that live in your gut also make other chemicals that affect how your brain works.

Your gut microbes produce lots of short-chain fatty acids (SCFA) such as butyrate, propionate and acetate.

They make SCFA by digesting fiber. SCFA affect brain function in a number of ways, such as reducing appetite.

Another SCFA, butyrate, and the microbes that produce it are also important for forming the barrier between the brain and the blood, which is called the blood-brain barrier.

Gut microbes also metabolize bile acids and amino acids to produce other chemicals that affect the brain.

Bile acids are chemicals made by the liver that are normally involved in absorbing dietary fats. However, they may also affect the brain.

Your gut-brain axis is also connected through the immune system.

Gut and gut microbes play an important role in your immune system and inflammation by controlling what is passed into the body and what is excreted.

If your immune system is switched on for too long, it can lead to inflammation, which is associated with a number of brain disorders like depression and Alzheimer’s disease.

Lipopolysaccharide (LPS) is an inflammatory toxin made by certain bacteria. It can cause inflammation if too much of it passes from the gut into the blood.

This can happen when the gut barrier becomes leaky, which allows bacteria and LPS to cross over into the blood.

Inflammation and high LPS in the blood have been associated with a number of brain disorders including severe depression, dementia and schizophrenia.

Probiotics, prebiotics and the gut-brain axis

Gut bacteria affect brain health, so changing your gut bacteria may improve your brain health.

Probiotics are live bacteria that impart health benefits if eaten. However, not all probiotics are the same.

Probiotics that affect the brain are often referred to as psychobiotics.

Some probiotics have been shown to improve symptoms of stress, anxiety and depression.

Prebiotics, which are typically fibers that are fermented by your gut bacteria, may also affect brain health.

One study found that taking a prebiotic called galactooligosaccharides may mitigate depressive symptoms.

What foods support the gut-brain axis?

A few groups of foods are specifically beneficial for the gut-brain axis.

Here are some of the most important ones:

  • Omega-3 fats: These fats are found in oily fish and also in high quantities in the human brain. Studies in humans and animals show that omega-3s can increase good bacteria in the gut and reduce risk of brain disorders.
  • Fermented foods: Yogurt, kefir, and sauerkraut all contain healthy microbes such as lactic acid bacteria. Fermented foods have been shown to alter brain activity.
  • High-fiber foods: Whole grains, nuts, seeds, fruits and vegetables all contain prebiotic fibers that are good for your gut bacteria. Prebiotics can reduce stress hormone in humans.
  • Polyphenol-rich foods: Cocoa, green tea, olive oil and coffee all contain polyphenols, which are plant chemicals that are digested by your gut bacteria. Polyphenols increase healthy gut bacteria and may improve cognition.
  • Tryptophan-rich foods: Tryptophan is an amino acid that is converted into the neurotransmitter serotonin. Foods that are high in tryptophan include turkey, eggs and cheese.

The takeaway

The gut-brain axis refers to the physical and chemical connections between your gut and brain.

Millions of nerves and neurons run between your gut and brain. Neurotransmitters and other chemicals produced in your gut also affect your brain.

By altering the types of bacteria in your gut, it may be possible to improve your brain health.

Omega-3 fatty acids, fermented foods, probiotics and other polyphenol-rich foods may improve your gut health, which may benefit the gut-brain axis.