The Connection Between Brain and Gut Health

The Connection Between Brain and Gut Health

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Katie Stone - Naturopath

Written By:

Katie Stone - Naturopath
Dr. Nare Simonyan - PhD Pharmaceutical Science

Medical Reviewer:

Dr. Nare Simonyan - PhD Pharmaceutical Science
Kari Asadorian - BSN, RN

Edited By:

Kari Asadorian - BSN, RN
Last updated:
Gut Health and Brain Function | MTHFR | Supplement Review | Methyl-Life® Supplements Source: YouTube.com

What is the gut-brain connection?

The gut-brain axis is a continuous, bidirectional communication system between the central nervous system (the brain and spinal cord) and the enteric nervous system (the network of neurons living in the gut lining). It also includes the autonomic nervous system (ANS) and the hypothalamic pituitary adrenal (HPA) axis.


The gut microbiota is the most abundant and diverse microbiota in the body and plays a central role in producing metabolites and signaling molecules that influence the brain and immune function.2 The vagus nerve is the most widely distributed and complex nerve in the body, sending signals from the brain to the gut and also relaying information from the gut back to the brain regarding inflammation, satiety, and microbial activity.3


Around 200–600 million neurons live within the enteric nervous system (the lining of the gut).

This “second brain” operates semi-independently from the central nervous system and communicates with both microbes and immune cells in the gut. Together with the vagus nerve and microbiota, it forms the basis of the gut-brain axis.4

This system interacts with intestinal microbes, the intestinal immune system, and endocrine systems, creating a powerful network that helps to maintain the overall health and function of the gut.


The gut-brain axis includes: 

  • The nervous system: The vagus nerve acts as a direct line of communication between the brain and the gut. 
  • The endocrine system: Hormones released by the gut and brain influence appetite, satiety, and stress responses. 
  • The immune system: Immune signals between the gut and the brain regulate inflammation and overall health.


What is the purpose of the gut-brain connection?

The gut-brain axis allows the brain to influence digestion, immune function, and the stress response, while the gut can influence mood, behavior, and even cognitive functions.5


This communication system links emotional and cognitive centres in the brain with important gut functions, including immune responses, the gut barrier, reflexes and hormone signalling.6 These include areas such as the amygdala (emotion), hippocampus (memory), and prefrontal cortex (decision-making), all of which are influenced by signals originating in the gut.


What body functions are affected by the gut-brain connection?

The gut-brain axis influences many bodily systems, including digestion, hormone production and the activity of functional immune effector cells. The gut is able to influence mood, cognition and mental health. For example, changes in gut microbiome have been associated with depression and altered brain activity in emotional processing regions.7


Specifically, gut-brain communication may affect:

  • Cognitive function and mood: The gut microbiome produces a range of neurotransmitters (serotonin, dopamine), short-chain fatty acids (SCFAs), and other bioactive molecules that influence neural processes.8
  • Digestion: The brain can influence gut motility, secretion, and intestinal permeability through the CNS. Stress can trigger the ANS to alter gut motility, potentially causing diarrhea or constipation.
  • Appetite, cravings, satiety: Hormones secreted in the gut can affect brain regions involved in regulating appetite and feelings of fullness. 
  • Immune function: Gut microbiome can activate intestinal or circulating immune cells that can migrate to the CNS.9
  • Food sensitivities and intolerances: Visceral hypersensitivity can amplify pain and discomfort resulting from gut discomfort (e.g. bloating, cramping)
  • Metabolism: The gut releases hormones and peptides including glucagon-like peptide-1 and ghrelin, which influence appetite, satiety, and energy expenditure.10

Health conditions related to the gut-brain connection

The gut microbiome can influence systemic inflammation and metabolic function, and dysfunctions of the gut-brain axis have been linked to a range of chronic diseases.

Cardiovascular disease

Atherosclerosis (acute coronary syndrome and stroke), heart failure, and hypertension have been linked to dysbiosis. Atherosclerotic cardiovascular disease is characterized by high levels of harmful bacteria, including Enterobacteriaceae and Streptococcus.11

Type 2 diabetes

The gut-brain axis plays a key role in the control of blood sugar levels, with the enteric nervous system (ENS) relaying information about nutritional status to the hypothalamus. In type 2 diabetes, this communication is disrupted, which can lead to hyperglycemia and insulin resistance. ENS neurons are influenced by both nutrients and inflammatory signals, particularly from the gut.12

Weight gain and obesity

The brain is central to energy utilization by constantly monitoring the body’s metabolic state and adjusting behaviour and processes such as appetite, fat storage, heat production, and liver glucose output. A healthy connection between the brain, gut, and fat tissue helps maintain energy balance and body weight. When this communication breaks down, it can cause the body to take in more energy than it uses, potentially leading to obesity.13

Irritable bowel syndrome

The association between impaired barrier function and symptoms in IBS have been linked to visceral hypersensitivity. It is believed that mast cell-induced activation of enteric neurons may contribute to visceral hypersensitivity, causing pain. People with IBS also appear to have increased expression of Toll-like receptors (TLRs), which are found on many different cells, including intestinal epithelial cells and immune cells, as well as cytokines, which may cause intestinal inflammation.14

Alzheimer’s and cognitive decline

Dysbiosis can lead to increased permeability of the gut barrier and activation of the immune system, which then triggers systemic inflammation. Chronic inflammation is associated with impairments of the blood-brain barrier, causing neuroinflammation, damage to brain cells, and eventually neurodegeneration.15

Gut health and mental health

Many mental disorders including depression, schizophrenia, anxiety, and autism spectrum disorder have all been linked to imbalances in gut microbiota.15 Gut bacteria is shown to have a clear impact on neurotransmitter synthesis and availability, including serotonin, dopamine, GABA, and glutamate. Around 95% of total body serotonin is made in the gut, and low gut serotonin or disrupted serotonin signaling (due to gut inflammation or dysbiosis) can contribute to low mood and other imbalances.

Dysfunction of the gut microbiome can lead to disparities in neurotransmitters that are involved in depressive disorders through the microbiome-gut-brain axis, possibly caused by either an increase in neuroinflammation or a decrease in neuroplasticity and neurogenesis, with these effects being mediated by the HPA axis or vagus nerve.17

Several studies on mice have shown that the gut microbiota and their byproducts can have a positive or negative influence on behavior, which has been linked to autism. Other studies have found differences in the gut microbiome of children with autism, although further research is pending.18

The connection between brain and gut health

Key takeaways

  • Icon The gut and brain are in constant communication via the gut-brain axis.
  • Icon Imbalance of the gut microbiome can affect mood, cognition, cardiovascular function, and many other bodily systems.
  • Icon The gut plays a major role in mental health, and dysbiosis has been linked to depression, schizophrenia, autism and dementia.

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  • Assists Breakdown of Proteins, Carbohydrates, Lipids, Gluten & Dairy
  • Tastes like a natural, after-dinner mint
  • 3rd-Party Tested, Non-GMO, Gluten-Free, 90 Vegan Tablets

The Connection Between Gut Health and Brain Function

Frequently Asked Questions about the gut-brain axis

Is the gut-brain related to mental health?

Yes, the bidirectional connection between the gut and brain allows the gut to influence mental health, and the brain to influence gut function. Imbalances of the gut microbiota (dysbiosis) can disrupt this communication and affect neurotransmitter synthesis, which is associated with the many mental disorders including depression and schizophrenia.

Does your gut health affect your brain?

Yes, your gut health has a significant impact on your brain. Research has shown that the gut microbiome communicates with the brain through several pathways, mainly through the vagus nerve, a major nerve that connects the brain to the gut and other organs.
The balance of ‘good’ and ‘bad’ bacteria also play a part in brain function. Supplementation with the strain Lactobacillus rhamnosus has been shown to improve mood in anxious or depressed mice. But when the vagus nerve is blocked, this effect disappears, suggesting that the bacteria may be using the vagus nerve to send signals to the brain.19

Can gut issues cause neurological issues?

Yes, gut disorders such as Irritable Bowel Syndrome (IBS) and inflammatory bowel disorders have been linked to the development of neurodegenerative and neuropsychiatric conditions such as depression, anxiety, Alzheimer's disease, Parkinson's disease and even multiple sclerosis.
This may be partly due to leaky gut, which occurs when the gut barrier becomes damaged, allowing harmful substances to pass into the bloodstream and causing ongoing inflammation throughout the body. Although the brain is normally protected by the blood-brain barrier, this inflammation can weaken it, allowing immune cells to enter the brain and potentially affect brain function.

References

  1. Andrina Rutsch, Johan B. Kantsjö, Francesca Ronchi; "The Gut-Brain Axis: How Microbiota and Host Inflammasome Influence Brain Physiology and Pathology"; Frontiers in Immunology; 2020 Dec

    https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2020.604179/full

  2. Gun-Ha Kim, Jung-Ok Shim; "Gut microbiota affects brain development and behavior"; Clinical and experimental pediatrics; 2022 Nov

    https://pmc.ncbi.nlm.nih.gov/articles/PMC10331547/

  3. Yimin Han, Boya Wang, Han Gao, Chengwei He, Rongxuan Hua, Chen Liang, Sitian Zhang, Ying Wang, Shuzi Xin, Jingdong Xu; "Vagus Nerve and Underlying Impact on the Gut Microbiota-Brain Axis in Behavior and Neurodegenerative Diseases"; Journal of inflammation research; 2022 Nov

    https://pmc.ncbi.nlm.nih.gov/articles/PMC9656367/

  4. Zi-Han Geng, Yan Zhu, Quan-Lin Li, Chao Zhao, Ping-Hong Zhou; "Enteric Nervous System: The Bridge Between the Gut Microbiota and Neurological Disorders"; Frontiers in aging neuroscience; 2022 Apr

    https://pmc.ncbi.nlm.nih.gov/articles/PMC9063565/

  5. Kara G. Margolis, John F. Cryan, Emeran A. Mayer; "The Microbiota-Gut-Brain Axis: From Motility to Mood"; Gastroenterology; 2021 Jan

    https://www.gastrojournal.org/article/S0016-5085(21)00268-7/fulltext

  6. Marilia Carabotti, Annunziata Scirocco, Maria Antonietta Maselli, Carola Severi; "The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems"; Annals of gastroenterology; 2015 Apr-Jun

    https://pmc.ncbi.nlm.nih.gov/articles/PMC4367209

  7. G B Rogers, D J Keating, R L Young, M-L Wong, J Licinio, S Wesselingh; "From gut dysbiosis to altered brain function and mental illness: mechanisms and pathways"; Molecular psychiatry; 2016 Apr

    https://pmc.ncbi.nlm.nih.gov/articles/PMC4879184

  8. Wen Gao, Kelley L Baumgartel, Sheila A Alexander; "The Gut Microbiome as a Component of the Gut–Brain Axis in Cognitive Health"; Biological research for nursing; 2020 Jul

    https://pmc.ncbi.nlm.nih.gov/articles/PMC7874359

  9. Zi-Han Geng, Yan Zhu, Quan-Lin Li, Chao Zhao, Ping-Hong Zhou; "Enteric Nervous System: The Bridge Between the Gut Microbiota and Neurological Disorders"; Frontiers in aging neuroscience; 2022 Apr

    https://pmc.ncbi.nlm.nih.gov/articles/PMC9063565

  10. Maralyn R. Druce, Caroline J. Small, Stephen R. Bloom; "Minireview: Gut Peptides Regulating Satiety "; Endocrinology; 2004 Jun

    https://academic.oup.com/endo/article-abstract/145/6/2660/2878101

  11. Zhuye Jie, Huihua Xia, Shi-Long Zhong, Qiang Feng, Shenghui Li, Suisha Liang, Huanzi Zhong, Zhipeng Liu, Yuan Gao, Hui Zhao, Dongya Zhang, Zheng Su, Zhiwei Fang, Zhou Lan, Junhua Li, Liang Xiao, Jun Li, Ruijun Li, Xiaoping Li, Fei Li, Huahui Ren, Yan Huang, Yangqing Peng, Guanglei Li, Bo Wen, Bo Dong, Ji-Yan Chen, Qing-Shan Geng, Zhi-Wei Zhang, Huanming Yang, Jian Wang, Jun Wang, Xuan Zhang, Lise Madsen, Susanne Brix, Guang Ning, Xun Xu, Xin Liu, Yong Hou, Huijue, Kunlun He, Karsten Kristiansen; "The gut microbiome in atherosclerotic cardiovascular disease"; Nature communications; 2017 Oct

    https://pmc.ncbi.nlm.nih.gov/articles/PMC5635030/

  12. Arnaud Bessac, Patrice D Cani, Etienne Meunier, Gilles Dietrich, Claude Knauf; "Inflammation and Gut-Brain Axis During Type 2 Diabetes: Focus on the Crosstalk Between Intestinal Immune Cells and Enteric Nervous System"; Frontiers in neuroscience; 2018 Oct

    https://pmc.ncbi.nlm.nih.gov/articles/PMC6191495

  13. Aqsa Iqbal, Anis Rehman; "Obesity Brain Gut Adipocyte Interaction"; StatPearls [Internet]; 2023 Jul

    https://www.ncbi.nlm.nih.gov/books/NBK551660/

  14. Eline Margrete Randulff Hillestad, Aina van der Meeren, Bharat Halandur Nagaraja, Ben René Bjørsvik, Noman Haleem, Alfonso Benitez-Paez, Yolanda Sanz, Trygve Hausken, Gülen Arslan Lied, Arvid Lundervold, Birgitte Berentsen; "Gut bless you: The microbiota-gut-brain axis in irritable bowel syndrome"; World journal of gastroenterology; 2022 Jan

    https://pmc.ncbi.nlm.nih.gov/articles/PMC8790555/

  15. Karol Kowalski, Agata Mulak; "Brain-Gut-Microbiota Axis in Alzheimer’s Disease"; Journal of neurogastroenterology and motility; 2019 Jan

    https://pmc.ncbi.nlm.nih.gov/articles/PMC6326209/

  16. Amjad Mhanna, Nafiza Martini, Ghefar Hmaydoosh, George Hamwi, Mulham Jarjanazi, Ghaith Zaifah, Reem Kazzazo, Aya Haji Mohamad, Zuheir Alshehabi; "The correlation between gut microbiota and both neurotransmitters and mental disorders: A narrative review"; Medicine (Baltimore); 2023 Feb

    https://pmc.ncbi.nlm.nih.gov/articles/PMC10843545/

  17. Maria Luca, Maurizio Di Mauro, Marco Di Mauro, Antonina Luca; "Gut Microbiota in Alzheimer’s Disease, Depression, and Type 2 Diabetes Mellitus: The Role of Oxidative Stress"; Neuropsychiatric Disturbances and Diabetes Mellitus: The Role of Oxidative Stress; 2019 Apr

    https://onlinelibrary.wiley.com/doi/10.1155/2019/4730539

  18. Giselle C. Wong, Johanna M. Montgomery, Michael W. Taylor; "Chapter 8 The Gut-Microbiota-Brain Axis in Autism Spectrum Disorder"; Autism Spectrum Disorders [Internet]; 2021 Aug

    https://www.ncbi.nlm.nih.gov/books/NBK573606/

  19. Javier A. Bravo, Paul Forsythe, Marianne V. Chew, Emily Escaravage, Hélène M. Savignac, Timothy G. Dinan, John Bienenstock, John F. Cryan; "Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve"; Proc. Natl. Acad. Sci. U.S.A.' 2011 Jul

    https://www.pnas.org/doi/10.1073/pnas.1102999108

Katie Stone - Naturopath

About the Author

Katie is a qualified Naturopath (BNatMed) and freelance writer from New Zealand. She specializes in all things health and wellness, particularly dietary supplements and nutrition. Katie is also a dedicated runner and has completed more half-marathons than she can count!

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