The Gut-Brain Connection: What Science Tells Us About Food and Mood

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.

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 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.

Neurotransmitters

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.

Gut microbes

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.

Probiotics, Prebiotics, and the Gut-Brain Axis

Emerging research has highlighted the significant role of the gut-brain axis—the bidirectional communication between the gastrointestinal tract and the central nervous system—in influencing mental health. Central to this relationship is the composition of gut bacteria, which can impact brain function and emotional well-being. Consequently, modifying the gut microbiome through dietary interventions such as probiotics and prebiotics has gained considerable attention as a potential strategy for supporting mental health.

Probiotics are live microorganisms that, when consumed in adequate amounts, confer health benefits to the host. However, not all probiotic strains exert the same effects. A subset known as psychobiotics has been specifically identified for their potential to influence the brain. Several studies suggest that certain psychobiotic strains can alleviate symptoms of stress, anxiety, and depression, offering a promising adjunct to conventional mental health treatments.

In addition to probiotics, prebiotics—non-digestible dietary fibers that serve as food for beneficial gut bacteria—may also play a role in mental health. These compounds undergo fermentation in the colon, promoting the growth of microbiota that can positively affect brain function. For instance, research has shown that a prebiotic known as galactooligosaccharides may help reduce depressive symptoms, underscoring the therapeutic potential of gut-targeted nutrition in psychological well-being.

Inflammation

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.

What Does Your Gut’s Brain Control?

Unlike the big brain in your skull, the ENS can’t balance your checkbook or compose a love note. Its main role is controlling digestion, from swallowing to the release of enzymes that break down food to the control of blood flow that helps with nutrient absorption to elimination. The enteric nervous system doesn’t seem capable of thought as we know it, but it communicates back and forth with our big brain—with profound results.

The ENS may trigger big emotional shifts experienced by people coping with irritable bowel syndrome (IBS) and functional bowel problems such as constipation, diarrhea, bloating, pain and stomach upset. For decades, researchers and doctors thought that anxiety and depression contributed to these problems. But our studies and others show that it may also be the other way around. Researchers are finding evidence that irritation in the gastrointestinal system may send signals to the central nervous system (CNS) that trigger mood changes.

These new findings may explain why a higher-than-normal percentage of people with IBS and functional bowel problems develop depression and anxiety. That’s important data, because up to 30% to 40% of the population has functional bowel problems at some point.