Gut-Brain Axis

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The Brain-Gut Axis is the concept of a "bi-directional intercommunication between the gut and the brain, providing an explanation of both the normal activity and acute and chronic perturbations of GI function."[1]

The Enteric Nervous System

The enteric nervous system (ENS) refers to the part of the nervous system that resides within the gut. "Even though it is now considered the third branch of the autonomic nervous system, the ENS has been referred to as the ‘second brain’, based on its size, complexity and similarity — in neurotransmitters and signalling molecules — with the brain."[2] "The ENS can be viewed as a peripheral extension of the limbic system into the gut, where it is exposed closely to our complex internal environment, including powerful mechanical, chemical and microbial influences. Alternatively, parts of the CNS [central nervous system] (in particular, pontine, autonomic and limbic circuits) can be viewed as an encephalized portion of the ENS."[2]


"The reciprocal impact of the gastrointestinal tract on brain function has been recognized since the middle of the nineteenth century."[3] And humans have long known how emotions like love, fear, or shame result in "butterflies in your stomach" or other sensations in the gut. More recently, scientists had observed that psychiatric problems such as anxiety and depression were common in patients with chronic gut disorders like inflammatory bowel disease and irritable bowel syndrome.[4][5] Animal studies had also shown that acute and chronic gut inflammation resulted in changes in behavior and central nervous system (CNS) biochemistry, although scientists did not understand how or why.[6][7][8][9] A Nestle-funded 2011 study found that mice with colitis exhibited anxiety-like behavior, but administration of a probiotic bacteria normalized behavior in the mice without influencing gut inflammation.[10] They also found that the vagus nerve is required for gut-brain communication. Another 2011 study found that the colonization of the gut by microbiota early in life impacts brain development and behavior in mice.[11]

Further Research

A 2013 UCLA study, funded by Danone, was the first to claim that the gut impacts the brain in humans (as opposed to the other way around). The study tested three groups of women.[12] One consumed yogurt with live cultures, one consumed a yogurt-like substance that contained no live cultures, and a third consumed nothing at all. The researchers looked at the women's brains before the study began and after four weeks. After four weeks, those who consumed yogurt with live cultures had differences in parts of their brains linked to emotions and sensory processing. The lead author, Kirsten Tillisch, was quoted saying, "Time and time again, we hear from patients that they never felt depressed or anxious until they started experiencing problems with their gut. Our study shows that the gut–brain connection is a two-way street."

Resources and articles

Related Sourcewatch articles


  1. Farmer AD, Randall HA, Aziz Q, "It's a Gut Feeling - how the gut microbiota affects the state of mind," J Physiol, March 24, 2014.
  2. 2.0 2.1 Emeran A. Mayer, "Gut feelings: the emerging biology of gut–brain communication," Nature Reviews Neuroscience, July 13, 2011.
  3. Cryan JF, Dinan TG, "Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour," Nature Reviews Neuroscience, October 2012.
  4. Walker JR, Ediger JP, Graff LA et al. The Manitoba IBD cohort study: a population-based study of the prevalence of lifetime and 12-month anxiety and mood disorders. Am J Gastroenterol 2008; 103: 1989–97.
  5. Whitehead WE, Palsson O, Jones KR. Systematic review of the comorbidity of irritable bowel syndrome with other disorders: what are the causes and implications? Gastroenterology 2002; 122: 1140–56.
  6. Lyte M, Varcoe JJ, Bailey MT. Anxiogenic effect of subclinical bacterial infection in mice in the absence of overt immune activation. Physiol Behav 1998; 65: 63–8.
  7. Goehler LE, Gaykema RP, Opitz N et al. Activation in vagal afferents and central autonomic pathways: early responses to intestinal infection with Campylobacter jejuni. Brain Behav Immun 2005; 19: 334–44.
  8. Bercik P, Verdu´ EF, Foster JA et al. Role of gut–brain axis in persistent abnormal feeding behavior in mice following eradication of Helicobacter pylori infection. Am J Physiol Regul Integr Comp Physiol 2009; 296: R587–94.
  9. Bercik P, Verdu EF, Foster JA et al. Chronic gastrointestinal inflammation induces anxiety-like behavior and alters central nervous system biochemistry in mice. Gastroenterology 2010; 139: 2102–12.
  10. Bercik P, Park AJ, Sinclair D, Khoshdel A, Lu J, Huang X, Deng Y, Blennerhassett PA, Fahnestock M, Moine D, Berger B, Huizinga JD, Kunze W, McLean PG, Bergonzelli GE, Collins SM, Verdu EF, "The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut-brain communication," Neurogastroenterol Motil, December, 2011.
  11. Rochellys Diaz Heijtz, Shugui Wang, et al, "Normal gut microbiota modulates brain development and behavior," PNAS, February 15, 2011.
  12. Rachel Champeau, "Changing gut bacteria through diet affects brain function, UCLA study shows," May 28, 2013, Accessed April 9, 2014.

External Resources

External Articles






  • Bercik P, et al. (2010) Chronic gastrointestinal inflammation induces anxiety-like behavior and alters central nervous system biochemistry in mice. Gastroenterology 139:2102–2112, e1.