Gut Brain Connection
The gut and brain are more connected than we make it out to be. Could it be true that there is more to the sayings “go with your gut,” “feeling sick to your stomach,” and “feeling butterflies in your stomach?” There is indeed still a lot we don’t know about the connection between the gut and the brain. Anatomically, the gut and the brain are linked physically by the vagus, splanchnic, and pelvic nerves. However, they are also connected through blood and various chemical messengers. The levels of these chemical messengers in your blood is heavily influenced by the population of microbes inside your gut.
What are Psychobiotics?
A psychobiotic is a probiotic or a gut bacteria that is capable of influencing brain & mental health. Probiotics are live microbes that are taken as supplements or eaten as components of fermented foods such as yogurt that live in the gut and have an impact on your physiologic health which then may influence your mental health.
Psychobiotics - Probiotics and Mental Health
The neurotransmitter commonly associated with happiness is serotonin. Pharmaceutical anti-depressants work by increasing serotonin levels in the. Interestingly, 90% of the serotonin produced in the body is produced by enterochromaffin cells of the gut where it is used to regulate bowel movements.[10] However, serotonin does not go from the gut to the brain because it is blocked by the blood-brain barrier. One of serotonin’s precursors, the amino-acid tryptophan, is able to cross the blood-brain-barrier. Taking tryptophan supplements is known to have anti-depressive effects[11].
In addition to being associated with lower serotonin levels, depression is also associated with inflammation. Depressed individuals were more likely to have systemic increases in inflammatory signaling molecules such as C-reactive protein (CRP), Interleukin-6 (IL-6), and Interleukin-10 (IL-10).[1] Instead of focusing on serotonin levels in the brain, a novel approach to depression could instead focus on lowering levels of inflammation throughout the body.
Inflammation is the body’s response to things that it finds irritating. An irritant causes release of chemical messengers followed by an immune response to the irritant. The body is constantly exposed to irritants on your skin as well as in your gut. It is no surprise that the majority of your immune system is centered around your gut where there are over 1012 organisms per gram of intestinal content.[2] Most of those organisms are benign and others are beneficial. The beneficial ones are called probiotics. Probiotics are known good beneficial bacteria that can be either consumed through food or through concentrated supplements. They take up residence inside the large intestine and compete against bad and undesirable bacteria.
These bad organisms can cause irritation of the cells that line the gut would cause them to release more inflammatory compounds that wind up in the bloodstream and in systemic circulation. They can also release inflammatory molecules themselves. For example, E. coli organisms produce pro-inflammatory lipopolysaccharide (LPS) endotoxins. Interestingly, excessive LPS levels in animals has been shown to cause depression-like behavior in animals.[3]
Probiotics and Depression
Probiotic administration decreases levels of LPS endotoxins into the body[4]. Probiotic supplements have also been found to mediate and lower systemic release of inflammatory cytokines[5], and reduce levels of the pro-inflammatory molecule interleukin-1 alpha (IL-1-α)[6]. Therefore, it is reasonable to expect probiotic supplementation would have an effect on mood and depression. Indeed, in one triple-blinded study of healthy human subjects researchers found that supplementation with a multispecies probiotic formulation consisting of Lactobacillus and Bifidobacterium probiotics reduced sad mood and rumination compared to placebo control.[7]
Psychobiotics & Anxiety
Animal studies reinforce this idea of a gut-brain connection through probiotics. Mice brought up in a germ-free environment were anxious and more easily stressed than normal mice. This stressed-out and anxious behavior was reversed with the administration of Bifidobacterium infantis probiotic.[8] The same researchers found that germ free mice had lower levels of the neurotransmitters norepinephrine and 5-hydroxytryptamine (5-HT) in the brain.[9] 5-HT is the precursor to the “happy neurotransmitter” serotonin. As mentioned before most anti-depressant medications work by increasing the levels of serotonin in the brain.
The Future of Psychobiotics
More research is required to fully elucidate the gut-brain connection but what is clear is that depression and other mood disorders are caused by chemical imbalances in the brain. However, these imbalances are not limited to neurotransmitters in the brain but could also involve inflammatory signaling molecules that make their way from the gut to the brain. Probiotics lower inflammation by competing against pro-inflammatory microbes in the gut and by lowering the body’s production of inflammatory cytokines. Other foods that lower inflammation include fish oil, ginger, green tea, and turmeric.
[1] http://journals.lww.com/psychosomaticmedicine/Abstract/2009/02000/Associations_of_Depression_With_C_Reactive.6.aspx
[2] https://www.ncbi.nlm.nih.gov/pubmed/12583961
[3] https://www.ncbi.nlm.nih.gov/pubmed/21194425
[4] https://www.ncbi.nlm.nih.gov/pubmed/19353762
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2654141/
[6] https://gutpathogens.biomedcentral.com/articles/10.1186/1757-4749-3-1
[7] http://www.sciencedirect.com/science/article/pii/S0889159115000884
[8] https://www.ncbi.nlm.nih.gov/pubmed/15133062
[9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664925/
[10] http://themedicalbiochemistrypage.org/nerves.html#5ht
[11] https://www.sciencedirect.com/science/article/pii/S0140673667918946
About the Author:
Dr. Bryan Do, D.O. is an osteopathic physician whose research interests include gastroenterology, immunology, and dermatology. He is particularly interested in the role of probiotics in the gut-brain-skin axis and has written many articles on the topic. He graduated from University of California, Los Angeles (UCLA) before graduating from Marian University College of Osteopathic Medicine in Indianapolis, Indiana and becoming a Doctor of Osteopathic Medicine. Osteopathic physicians are taught to take a holistic approach to medicine and to consider mind, body, and spirit when treating a patient. Osteopathic physicians receive training in Osteopathic Manipulative Medicine (OMM) in addition to the standard rigorous medical school curriculum. Both physicians with a Doctor of Osteopathic Medicine (D.O.) degree as well as a Doctor of Medicine (M.D.) can practice medicine.