Gut Feeling: The Brain-Gut Connection
Published in To Your Good Health, a natural health journal, Winter 2014, Issue #1
Does our gut really have the capacity to “feel”? If you have ever had food cravings when you are feeling down, or digestive upset in anticipation of a stressful event, then the connection certainly appears to be as real as anything else you experience. In fact, research in the growing field of psychoneuroimmunology (which looks at how the fields of psychology, neurology, and immunology blend together) shows that the nervous system of the gut, called the enteric nervous system (ENS), responds to more than 30 neurotransmitters. In fact, the ENS contains approximately 95% of the body’s serotonin, also known as the “feel good hormone” (Hadhazy, 2010). Because of its complex nervous system, the gut is now often referred to as the second brain. It is closely linked to the central nervous system of the brain (CNS) through the peripheral nervous system (PNS), which leaves the spinal cord and connects to different organs, including the gut. Being aware of this strong connection between the brain and the gut, naturopathic doctors typically target both the gut and the brain when managing mental health conditions such as depression, anxiety, autism, and ADHD.
The connection between the brain and the gut is no longer thought of as unidirectional, top-down control (Stasi et al., 2012). Research actually points to a predominance in the other direction: 90% of the nerve fibers in the vagus nerve (the primary nerve connecting the CNS and the ENS) carry information from the gut to the brain (Nibber et al., 2013)! In addition, the 100 trillion microbes residing in the gut are also involved in neurotransmitter production and therefore influence our mental well-being (Nibber et al., 2013). As a naturopathic doctor, optimizing digestive health is an integral part of almost every treatment plan, with the added bonus of its downstream effects on improving mental health. As well, because of the close link between the gut and input from the nervous and endocrine systems, stress management is an important component in helping to address digestive issues.
Food sensitivities can sensitize nerves in the gut, which in turn can trigger changes in the brain (Nibber et al., 2013). These changes can occur so insidiously that it may be difficult for the patient to pinpoint the culprit. This happened in the case of a 43 year old female who presented to my office with chief concerns of weight gain, fatigue, and generalized aches and pains. She was not on any medication at the time, but had a history of depression. Although she had daily bowel movements, her stools were sometimes loose, and she experienced bloating, which she attributed to excessive hunger and overeating. A careful look through her diet diary and questioning revealed that her diet was high in wheat and glutinous grains, and that her chief concerns had become more pronounced after eating more gluten on a regular basis. Within 5 days of removing gluten from her diet, she found that her stools were more solid, she had more energy, and had increased mental clarity. We continued on a gluten-free diet for 3 weeks, along with botanical medicine to support liver detoxification, and nutraceutical adrenal support due to the long-term stress she was under (confirmed by a Koenisburg adrenal urine stress test). At her next follow-up, food cravings had much improved, and she had lost 12 pounds over the previous 5 weeks. The mental clarity which she had originally experienced persisted while she avoided gluten. Physical injuries which had previously lingered on were now healing faster. If occasionally she ingested gluten, she would experience loose stools, nausea, and headaches. This case exemplifies how certain foods can trigger mood and behavioural changes. While gluten is a common culprit, food sensitivities are highly individual and must be properly evaluated, either through careful elimination and re-introduction, or through blood testing where appropriate.
As well, it is important not to forget about the role of commensal bacteria in the gut in helping achieve better mental health. Studies in mice showed that supplementation with specific probiotic strains, Lactobacillus rhamnosus and Bifidobacterium longus, decreased symptoms of anxiety and depression in these mice, through a vagus nerve-dependent mechanism (Grenham et al., 2011). Studies in mice also show that some probiotics increase resistance to stress by decreasing the release of stress-induced corticosterone (Grenham et al., 2011). Although to date we lack large randomized controlled trials in humans, Messaoudi et al. did find that a specific probiotic combination alleviated psychological distress in otherwise healthy volunteers in a small double blind, placebo-controlled, randomized clinical trial (2011). This may explain in part why strain-specific probiotics can be used to alleviate symptoms of conditions with a strong psychogenic link, such as irritable bowel syndrome.
The link between the gut and the brain is complex and multifactorial. For patients with mood and psychological distress, it is often a relief to find out that what they ingest can impact their mental health, and that it’s not all “in their heads”. Obversely, those presenting with digestive disturbances are often surprised by the alertness and mental clarity they experience once the health of their digestive system is improved.
Our first and second brains are in constant communication, and symptoms such as anxiety, depression, mental fog, and digestive upset are red flags to alert us that something is out of balance. Will you listen?
Grenham, S., Clarke, G., Cryan, J.F., and Dinan, T.G. (2011). Brain-gut-microbiome communication in health and disease, Frontiers in Physiology, December 07; 2(94): 1-15.
Hadhazy, A. (2010). Think Twice: How the Gut’s “Second Brain” Influences Mood and Well-Being, Retrieved August 23, 2013, from the Scientific American website:http://www.scientificamerican.com/article.cfm?id=gut-second-brain.
Messaoudi, M., Lalonde, R., Violle, N., Javelot, H., Desor, D., Nejdi, A. et al. (2011). Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects, Br J Nutr, Mar; 105(5): 755-64.
Nibber, T., O’Brien, C., McIntyre, C., Dumas, C.A., Chou, M, Al-Kawally, M. (2013). The Gut-Brain Connection, Advances in Orthomolecular Research, 4(3): 4-7.
Stasi, C., Rosselli, M., Bellini, M., Laffi, G., and Milani, S. (2012). Altered neuro-endocrine-immune pathways in the irritable bowel syndrome: the top-down and the bottom-up model,J Gastroenterol, Nov; 47(11): 1177-85.
Dr. Tamar Ferreira is a Naturopathic Doctor in Brampton, Ontario. Her areas of focus include digestive health, hormone balance, and skin conditions.