The Gut-Brain Axis: How Your Gut and Brain Talk

The gut-brain axis is the two-way communication network between your digestive system and your brain. It runs through the vagus nerve, the nervous system in your gut wall, the immune system and chemical messengers made by gut bacteria. A major review describes how the trillions of microbes in the gut talk to the brain through these routes, including the vagus nerve, tryptophan metabolism and microbial products such as short-chain fatty acids (Cryan and colleagues, 2019). This guide explains how the gut and brain communicate, the role of serotonin, what research in people shows, and everyday ways to support a healthy gut.

It is educational, not medical advice.

Key Takeaways

• Two-way traffic: the gut and brain connect through nerves, immune signals, hormones and microbial products (Cryan and colleagues, 2019).
• The vagus nerve is a main line: it carries information about the state of your organs up to the brain (Breit and colleagues, 2018).
• Gut bacteria help make serotonin: much of the body's serotonin is made in the gut, and gut microbes help control how much (Yano and colleagues, 2015).
• Diet changes the microbiome fast: switching diets shifted gut bacteria within days in one study (David and colleagues, 2014).

What Is the Gut-Brain Axis?

The gut-brain axis is the name for the constant back-and-forth between your digestive tract and your brain. Your brain affects digestion, which is why stress can upset your stomach, and your gut sends signals that can influence the brain. Over the past 15 years, researchers have added gut microbes to the picture, so you will often see the term microbiota-gut-brain axis (Cryan and colleagues, 2019).

How Do the Gut and Brain Communicate?

• The vagus nerve: the main nerve of the parasympathetic nervous system, which helps oversee mood, immune response, digestion and heart rate, and sends information about the inner organs to the brain (Breit and colleagues, 2018).
• The enteric nervous system: a network of nerves in the gut wall, sometimes called the second brain (Cryan and colleagues, 2019).
• The immune system: immune signals made in the gut can reach the brain (Cryan and colleagues, 2019).
• Microbial chemicals: gut bacteria produce compounds such as short-chain fatty acids and affect tryptophan, the building block of serotonin (Cryan and colleagues, 2019).
• Gut hormones: the gut releases hunger and fullness signals such as ghrelin and OEA; see our guide to ghrelin and leptin.

The Gut and Serotonin

The digestive tract contains much of the body's serotonin. In research in mice and with human gut bacteria, certain spore-forming bacteria raised serotonin production by special cells in the colon, and that gut serotonin affected gut movement and blood platelets (Yano and colleagues, 2015). Serotonin made in the gut does not cross into the brain directly, but it shows how closely gut microbes and body chemistry are linked. Our guides to how to boost serotonin naturally and dopamine vs serotonin cover the brain side.

What Research in People Shows

Most gut-brain research so far has been in animals, and human studies are still small. Two examples:

• Probiotic fermented milk and brain activity: in 36 healthy women, 4 weeks of a fermented milk product with probiotics changed brain activity during an emotional attention task on brain scans, compared with a non-fermented milk or nothing (Tillisch and colleagues, 2013).
• Fermented foods and the microbiome: in a 17-week randomized study of healthy adults, a diet high in fermented foods steadily increased gut microbiome diversity and lowered inflammatory markers (Wastyk and colleagues, 2021).

These findings are promising, but they do not yet show that changing your gut bacteria will change how you feel day to day.

Stress and the Gut

The connection runs both ways. The vagus nerve links the brain to digestion and heart rate (Breit and colleagues, 2018), which helps explain why stress, nerves or a big presentation can show up as stomach upset. Slow breathing, regular movement and enough sleep support the calm side of the nervous system; our stress, mood and nervous system balance hub covers this in more depth. Some of the body's own messengers also link the gut and brain, such as OEA, which the small intestine makes after meals; our Anandamide Supplement pairs OEA with anandamide, PEA and L-theanine to support calm and a steady mood.

How to Support Your Gut-Brain Axis

• Eat plenty of plants: in a study that switched people between entirely plant-based and entirely animal-based diets, gut bacteria changed within days (David and colleagues, 2014).
• Add fermented foods: yogurt, kefir, kimchi, sauerkraut and kombucha increased microbiome diversity in a 17-week study (Wastyk and colleagues, 2021).
• Get enough fiber: beans, whole grains, vegetables and fruit feed gut bacteria.
• Manage stress: the vagus nerve links stress and digestion (Breit and colleagues, 2018).
• Sleep well and move daily: both support the nervous system and overall health.
• Use antibiotics only when needed: in one study, microbiome changes from a course of amoxicillin were still present 42 days after it ended (Pallav and colleagues, 2014).

Mushrooms and the Gut

Some mushrooms contain fibers called beta-glucans and other polysaccharides that gut bacteria can use. In a small randomized trial in 24 healthy volunteers, a turkey tail mushroom extract called PSP produced clear and consistent changes in the gut microbiome, in line with prebiotic activity (Pallav and colleagues, 2014). Learn more on our turkey tail ingredient page and our lion's mane ingredient page, and in our guide to lion's mane for brain health.

For more on the turkey tail trial and the lab research on gut bacteria, see our guide to turkey tail mushroom benefits.

Maitake, another mushroom in Forage, has its own trials in healthy adults; see our guide to maitake mushroom benefits.

Our Forage provides seven mushroom fruiting body extracts at 8:1 strength per two-capsule serving: reishi, lion's mane and cordyceps (200 mg each); chaga, maitake, turkey tail and shiitake (150 mg each); plus Himalayan shilajit (100 mg) and ashwagandha root extract (100 mg). The Mood Stack combines Kanna Nasal Spray, Anandamide and Lithium Orotate in one daily mood routine. Talk to your doctor before starting a supplement if you are pregnant, breastfeeding or take medication. For how turkey tail compares with reishi, see reishi vs turkey tail.

When to See a Doctor

See a doctor if you have ongoing stomach pain, diarrhea or constipation, blood in your stool, weight loss you cannot explain, or low mood or anxiety that lasts more than two weeks or affects daily life. Gut and mood symptoms can have many causes that are worth checking.

Frequently Asked Questions

What is the gut-brain axis in simple terms?

The two-way communication line between your digestive system and your brain, carried by nerves, hormones, immune signals and gut bacteria (Cryan and colleagues, 2019).

How does the gut talk to the brain?

Mainly through the vagus nerve, the gut's own nervous system, immune signals and chemicals made by gut bacteria (Cryan and colleagues, 2019; Breit and colleagues, 2018).

Is serotonin made in the gut?

Yes, much of the body's serotonin is made in the gut, and gut bacteria help control how much (Yano and colleagues, 2015).

Can gut health affect mood?

Research suggests a link, but human studies are still small. In one, a probiotic fermented milk changed brain activity on scans in healthy women (Tillisch and colleagues, 2013).

What is the vagus nerve?

The main nerve of the parasympathetic nervous system; it connects the brain with the gut and other organs (Breit and colleagues, 2018).

How can I improve my gut-brain connection?

Eat plenty of plants and fiber, add fermented foods, manage stress and sleep well (David and colleagues, 2014; Wastyk and colleagues, 2021).

How quickly does diet change the gut microbiome?

Fast: in one study, switching diets changed gut bacteria within days (David and colleagues, 2014).

Are fermented foods good for the gut?

In a 17-week study, a high-fermented-food diet increased microbiome diversity and lowered inflammatory markers (Wastyk and colleagues, 2021).

Sources

• Cryan JF, O'Riordan KJ, Cowan CSM, et al. The microbiota-gut-brain axis. Physiol Rev. 2019. PubMed 31460832
• Breit S, Kupferberg A, Rogler G, Hasler G. Vagus nerve as modulator of the brain-gut axis in psychiatric and inflammatory disorders. Front Psychiatry. 2018. PubMed 29593576
• Yano JM, Yu K, Donaldson GP, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell. 2015. PubMed 25860609
• Tillisch K, Labus J, Kilpatrick L, et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013. PubMed 23474283
• David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014. PubMed 24336217
• Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021. PubMed 34256014
• Pallav K, Dowd SE, Villafuerte J, et al. Effects of polysaccharopeptide from Trametes versicolor and amoxicillin on the gut microbiome of healthy volunteers: a randomized clinical trial. Gut Microbes. 2014. PubMed 25006989

These statements have not been evaluated by the Food and Drug Administration. This content is for education and is not medical advice. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk with a healthcare provider before starting a new supplement if you are pregnant, breastfeeding or taking medication.