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The Gut: Our Second Brain

By: Camryn Murray, Winthrop University Nutrition Student

Have you ever wondered why people refer to their stomach as their “second brain?” This

probably has something to do with something called the gut-brain axis.

What is the gut-brain axis?

The gut-brain axis is the common name for communication between the digestive system and the

central nervous system. The connection between the two is not completely understood within the

scientific world, but evidence suggests that the condition of our digestive health can significantly

impact our mood, sleep, brain, and overall health. Scientists believe that this connection has a lot

to do with the balance of bacteria in our intestines, which is referred to as our gut microbiota.

Where is our gut microbiota?

When people say, “gut health” or “gut microbiome,” they are most often referring to the bacteria

in the large intestine, specifically the cecum. Most of our food is digested and absorbed in the

small intestines but the large intestine finishes up the process by digesting and absorbing water, salts, and short-chain fatty acids that come from fiber. An imbalance between “good” bacteria and “bad” bacteria is called dysbiosis and is a phenomenon that is believed to affect overall health due to the gut’s relevance in almost every other body system.

Some ways dysbiosis can affect us:

  • Mood: Several neurotransmitters, like serotonin, dopamine, or GABA, is produced by the gut microbiome. Serotonin is known as the “happiness hormone,” and is important for regulating mood. Research shows that about 90% of serotonin is produced from bacteria like Lactobacillus, Bifidobacteria, Enterococcus, and Streptococcus in the gut.

  • Chronic disease: Research shows that patients with multiple sclerosis, Alzheimer's disease, Parkinson’s disease, and other mental health conditions have dysbiosis in their gut.

  • Stomach issues: The bacteria in our intestines release a lot of chemicals and gas, so imbalances in our microbiome can lead to bloating, discomfort, and even conditions like irritable bowel syndrome.

How can we promote bacterial diversity in our gut?

To try and avoid dysbiosis, we can do a few things to promote diversity in the types of bacteria

in our digestive system:

  1. Get adequate sleep and physical activity

  2. Eat a diverse, balanced diet, and don’t forget your fruits or vegetables! According to the 2016 American Gut Project, the #1 predictor of gut health is the diversity of plants in our diet

  3. Eat enough fiber; try swapping refined grains for whole grains

  4. Try some fermented foods like kimchi or kombucha

  5. Surprisingly, some research shows an association between better gut health and owning a dog as a child, possibly because dog owners are more often outdoors with their dogs

  6. Try to avoid being “too clean,” as a hyper-sterile environment and anti-bacterial sprays could reduce bacteria diversity (another possible reason why pets can be good for gut health)


1. Rutsch A, Kantsjö JB, Ronchi F. The gut-brain axis: How microbiota and host

Inflammasome Influence Brain Physiology and pathology. Frontiers in Immunology.

2020;11. doi:10.3389/fimmu.2020.604179

2. Liang S, Wu X, Hu X, Wang T, Jin F. Recognizing depression from the

microbiota–gut–brain axis. International Journal of Molecular Sciences. 2018;19(6):1592.


3. Wang Z, Wang Z, Lu T, et al. The microbiota-gut-brain axis in sleep disorders. Sleep

Medicine Reviews. 2022;65:101691. doi:10.1016/j.smrv.2022.101691

4. Smith RP, Easson C, Lyle SM, et al. Gut microbiome diversity is associated with sleep

physiology in humans. PLOS ONE. 2019;14(10). doi:10.1371/journal.pone.0222394

5. Tun HM, Konya T, Takaro TK, et al. Exposure to household furry pets influences the gut

microbiota of infants at 3–4 months following various birth scenarios. Microbiome.

2017;5(1). doi:10.1186/s40168-017-0254-x

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