Have you ever heard the phrase that our gut is our second brain? Well, this couldn’t be more true.

The relationship between the central nervous system (our brain and spinal cord) and the enteric nervous system (our digestive system), also known as the “gut-brain axis” is a profound system that reflects the way that the digestive system and the brain react with one another. The enteric nervous system is responsible for the release of hormones and neurotransmitters (i.e, gastrin, ghrelin, leptin, acetylcholine, secretin, etc.) to the brain that signify feelings of fullness, hunger, and gastric emptying, etc (Gropper & Smith, 2018).

The brain also communicates with the gut by different factors like slowing down/speeding up digestion, abdominal pain, and diarrhea from various stimuli, such as in the “fight or flight” response. Individuals who struggle with GI problems often lead to the patient developing chronic stress or anxiety because of the toll these conditions play in their everyday lives. However, researchers are now finding that individuals who struggle with anxiety, depression, and other psychiatric conditions often end up leading to the development of GI conditions, such as Irritable Bowel Syndrome or Peptic Ulcers (Mariotti, 2015). This leads us to believe that the mechanism between the gut and the brain works in both directions. This finding has been profound as it provides hope that altering the gut microbiome might play a role in minimizing chronic diseases and psychiatric conditions.

The gut microbiome is said to be the largest portion of the body’s immune system. The gut microbiome is made up of over 1,000 species of bacteria and organisms that play a role in proper digestion and immune functioning (Gropper & Smith, 2018). When the gut is lacking healthy bacteria, the immune system functioning is altered, and digestion is impaired. A recent study has been conducted that when increasing levels of stress from various stimuli (including; environmental, psychological, and physical stressors) have shown to decrease the activity of the gut microbiota, leading to increased susceptibility to developing infections and illness in military personnel (Karl, et al., 2018). The study reported that there were profound changes in the gut microbiota composition and metabolites, leading to drastic inflammation and decreased GI functioning.

The human body possesses powerful mechanisms when it comes to dealing with stress. The way that each individual perceives these stressors, determines how the body will handle that certain stimuli. Individuals who tend to positively cope with stress, will have better feedback mechanisms for developing how quickly the stress responses in the body will be turned on or off. But, the problem occurs with individuals who struggle with stress over a long period of time; who do not possess the adaptations to cope with these circumstances (Karl, et al., 2018).

When stress levels are high, the cortical center in the brain responds to the stimuli by activating pathways in the peripheral networks, including the sympathetic-adrenal-medullary axis, the renin-angiotensin system, as well as the hypothalamic-pituitary-adrenal axis (Mariotti, 2015). With all these pathways activated, a cascade of events occurs, which include the release of adrenaline, epinephrine, neuropeptides, and other hormones that regulate cardiovascular and metabolic functioning. These hormones and neuropeptides cause an increased heart rate, glucose release, and increased ventilation. When these hormones are high, glucocorticoids (corticotropin-releasing hormone and adrenocorticotropin-hormone) are released and thus stimulate levels of cortisol in the blood, which works to decrease inflammation and stimulating a negative-feedback mechanism (Mariotti, 2015). However, when stress remains constant over a long period of time, the receptors for these glucocorticoids become resistant and stress hormones in the blood remain high. This leads to a compromised immune system and damage to organs and tissues. This ongoing damage to tissues and organs will increase the levels of cytokines circulating in the blood that will mark cells for destruction and raise levels of inflammation throughout the body (Carnegie Mellon University, 2012).

References

Carnegie Mellon University. (2012, April 2). How stress influences disease: Study reveals inflammation as the culprit. ScienceDaily. Retrieved August 9, 2019 from www.sciencedaily.com/releases/2012/04/120402162546.htm

Gropper, S. A., & Smith, J. L. (2018). Advanced nutrition and human metabolism. Boston, MA: Cengage Learning.

Karl, J. P., Hatch, A. M., Arcidiacono, S. M., Pearce, S. C., Pantoja-Feliciano, I. G., Doherty, L. A., & Soares, J. W. (2018). Effects of Psychological, Environmental and Physical Stressors on  the Gut Microbiota. Frontiers in microbiology, 9, 2013. doi:10.3389/fmicb.2018.02013

Mariotti A. (2015). The effects of chronic stress on health: new insights into the molecular mechanisms of brain-body communication. Future science OA, 1(3), FSO23. doi:10.4155/fso.15.21