The Gut-Brain Connection

Rebecca Jaspan, MPH, RD, CDN, CDCES

Have you ever had butterflies in your stomach from nervousness or excitement? Or have you ever heard of having a gut feeling? These feelings and sensations are not only expressions, but actually suggest that the gut and brain are connected. Recent research shows that the health of your gut may affect your brain and vice versa, your brain may affect your gut health. Most of this evidence comes from the dysbiosis, or disruption to the microbiota balance, in the gut that is associated with central nervous system disorders and gastrointestinal disorders.1 The health of the gut-brain connection may be improved through a number of different ways, including the foods we eat and stress management techniques.

What is the gut-brain axis?

The gut-brain axis is the communication system between your gut and your brain. This system links emotional and cognitive centers of the brain with peripheral intestinal functions. A better understanding of the relationship between the brain and gut may help provide targeted therapies and treatments for a number of gastrointestinal and mental health disorders such as irritable bowel syndrome, depression, and anxiety.1

The bidirectional communication network between the brain and the gut includes the central nervous system (CNS), spinal cord, the autonomic nervous system (ANS), the enteric nervous system (ENS), and the hypothalamic pituitary adrenal (HPA) axis. In response to any form of stress, these systems release cortisol, the major stress hormone that affects many organs, which influences the activity of intestinal and immune cells.1 These cells are largely affected by the gut microbiota, which is where our gut health comes into play.2

The gut microbiome is the diverse network of bacteria that resides in the human gut. Each person’s microbiota is distinct, though the abundance and distribution of the microbiota along the intestine is similar among health individuals. The most prominent bacteria in the gut are Firmicutes and Bacteroides, accounting for at least three-quarters of the microbiome. The presence of diverse gut microbiota has important metabolic and physiological functions.3

The final important component of the gut-brain axis is the vagus nerve, one of the largest nerves in the body that connects the brain and the gut. Your gut contains 500 million neurons and the vagus nerve helps send signals in both directions.4 The vagus nerve is thought to play an important role in both gut and brain health. One study found that individuals with irritable bowel syndrome or Crohn’s disease had reduced vagal tone, indicating that the function of the vagus nerve was reduced.5

Why is the gut-brain axis important?

Research shows that chronic stress alters intestinal permeability. This is associated with low-grade inflammation and many health conditions including psychiatric disorders such as depression.6 There is increasing interest in determining how the gut microbiota may influence and contribute to the development and pathogenesis of neuropsychiatric disorders. For example, dopamine is a key neurotransmitter associated with schizophrenia. It is possible that bacterial metabolites in the gut interact with and stimulate the central and peripheral nervous system.

It is also well established that the response of the central nervous system to psychological and physical stressors can affect gut homeostasis and contribute to the development of diseases such as ulcerative colitis and irritable bowel syndrome. Frequently, one primary treatment of irritable bowel syndrome is stress management along with dietary changes and possible medication.7

How do you improve the gut-brain connection?

There is a large body of research to suggest that gut bacteria affect brain health, so altering your gut bacteria may improve your brain health. There are certain groups of foods that are beneficial for the gut-brain axis. Omega-3 fatty acids are found in oily fish such as salmon and tuna, flaxseed, walnuts, and plant oils. They are needed for brain health and studies show that they can increase the good bacteria in the gut, reducing the risk of brain disorders.8

Fermented foods such as yogurt, kefir, and sauerkraut, contain healthy gut bacteria and are shown to alter brain activity.9 Foods that are high in fiber such as whole grains, nuts, seeds, fruits and vegetables are considered prebiotics, which is food for the healthy bacteria in your gut. Research shows that prebiotics may reduce cortisol in humans.10

What about probiotics?

Probiotics are live bacteria in the gut and research shows that the greater diversity of gut microbiota we have, the healthier our gut is. Probiotics may impart health benefits when eaten or taken as a supplement. There are also specific probiotics that are thought to affect the brain, called psychobiotics.11 Some probiotics have been shown to improve symptoms of stress, anxiety, and depression. One small study looked at individuals with irritable bowel syndrome and anxiety and depression. The study found that taking a probiotic for six weeks significantly improved symptoms.12 Think you may benefit from increasing gut healthy foods in your diet or taking a probiotic? Speak with your registered dietitian and they can help you come up with a plan that is specific to your individual needs.

References

1. Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroenterol. 2015;28(2):203-209.
2. Mayer EA, Savidge T, Shulman RJ. Brain-gut microbiome interactions and functional bowel disorders. Gastroenterology. 2014;146:1500–1512
3. Eckburg PB, Bik EM, Bernstein CN, et al. Diversity of the human intestinal microbial flora. Science. 2005;308:1635–1638
4. Mayer EA. Gut feelings: the emerging biology of gut-brain communication. Nat Rev Neurosci. 2011;12(8):453-466. Published 2011 Jul 13. doi:10.1038/nrn3071
5. Pellissier S, Dantzer C, Mondillon L, et al. Relationship between vagal tone, cortisol, TNF-alpha, epinephrine and negative affects in Crohn’s disease and irritable bowel syndrome. PLoS One. 2014;9(9):e105328. Published 2014 Sep 10. doi:10.1371/journal.pone.0105328
6. Kelly JR, Kennedy PJ, Cryan JF, Dinan TG, Clarke G, Hyland NP. Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders. Front Cell Neurosci. 2015;9:392. Published 2015 Oct 14. doi:10.3389/fncel.2015.00392
7. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/treatment
8. Menni C, Zierer J, Pallister T, et al. Omega-3 fatty acids correlate with gut microbiome diversity and production of N-carbamylglutamate in middle aged and elderly women. Sci Rep. 2017;7(1):11079. Published 2017 Sep 11. doi:10.1038/s41598-017-10382-2
9. Tillisch K, Labus J, Kilpatrick L, et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013;144(7):1394-1401.e14014. doi:10.1053/j.gastro.2013.02.043
10. Schmidt K, Cowen PJ, Harmer CJ, Tzortzis G, Errington S, Burnet PW. Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology (Berl). 2015;232(10):1793-1801. doi:10.1007/s00213-014-3810-0
11. Dinan TG, Stanton C, Cryan JF. Psychobiotics: a novel class of psychotropic. Biol Psychiatry. 2013;74(10):720-726. doi:10.1016/j.biopsych.2013.05.001
12. Pinto-Sanchez MI, Hall GB, Ghajar K, et al. Probiotic Bifidobacterium longum NCC3001 Reduces Depression Scores and Alters Brain Activity: A Pilot Study in Patients With Irritable Bowel Syndrome. Gastroenterology. 2017;153(2):448-459.e8. doi:10.1053/j.gastro.2017.05.003



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