The Gut-Brain Axis: A Bidirectional Communication

Written by Kelsey Schaffstall Young MS, RDN, CDN, LDN

What is the Gut-brain axis?

The human large intestine is home to a bacteria rich environment, also known as the gut
microbiome. More than 1,000 species of bacteria have been identified in the human gut and,
on average, a person carries approximately 160 different species. 1 These bacteria not only have
an impact on the digestive system, but on the brain as well, due to their connection to the
nervous system which is referred to as the “gut-brain axis”.
Research continues to explore the characteristics of a healthy gut microbiome, the flow
of information between the gut and the brain, and the impact of diet on gut health.

How are the gut and the brain connected?

One of the largest nerves in the body, known as the vagus nerve, connects the gut to the
central nervous system and supports the flow of information in both directions. 1 The vagus
nerve receives a variety of messages from the gut via sensing cells in the gut lining. One
substance these cells are sensitive to is short chain fatty acids or SCFAs. These byproducts of
gut bacteria metabolism can impact the brain by promoting the synthesis of neurotransmitters
such as serotonin, dopamine, and melatonin which act as chemical messengers to the central
nervous system and impact bodily functions such as mood, behavior, and sleep. 1

What is a healthy gut?

Gut health is challenging to define due to the variation seen between individuals.
Research is beginning to recognize the importance of the function of an individual’s microbiome
versus its bacterial composition alone. 1 Some characteristics of a healthy gut microbiome
include microbial richness and diversity (the number and variety of microbes) as well as
resistance to disruptions and the resilience to return back to baseline after a disruption. 1

The impact of diet on the gut microbiome

Research has shown that diet can impact a person’s microbiome in a number of ways
including the number of gut bacteria, the diversity of the microbiome, and the metabolic
activity of the bacteria. Dietary patterns that have a positive impact on gut health are rich in
fibrous foods such as fruit, vegetables, and whole grains as well as fermented foods, nuts,
unsaturated fatty acids, and plant proteins. 1 A diet rich in animal protein, saturated fat, and
added sugar has been shown to decrease microbial diversity and function, decrease beneficial
bacteria, and increase opportunistic pathogens. 1

Nutrition strategies to improve gut health

In order to improve gut health, consume probiotic foods such as sauerkraut, sourdough,
kimchi, kefir, yogurt, miso, and kombucha. These foods contain live and active beneficial
bacteria that will help add to the richness and diversity of your microbiome.
Consuming probiotic foods will introduce beneficial bacteria into your gut, but it is
arguably even more important to ensure that you are consuming a variety of prebiotic foods
that contain fiber which nourishes gut bacteria, allowing them to survive and thrive. Examples
of prebiotic foods include garlic, onions, bananas, apples, oats, asparagus, artichokes, and

If you are interested in learning more about the gut-brain connection and how to
improve your gut health, reach out to a Registered Dietitian who can assist you in making a
personalized nutrition plan.


1. Berding, Kirsten, et al. "Diet and the microbiota–gut–brain Axis: Sowing the seeds of
good mental health." Advances in Nutrition 12.4 (2021): 1239-1285.

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