The two-way (bidirectional) relationship between our brain and gut is often referred to as the gut-brain connection or gut-brain axis. The enteric nervous system (ENS) is a highly complex system of nerves found throughout the lining of the gut and generally communicates with the brain through the vagus nerve. An obvious example of this communication is triggered by the sight and/or smell of a meal. The parasympathetic nervous system (part of the central nervous system) sends signals to the ENS, which causes a release of digestive secretions in both the mouth and stomach. These signals also prepare muscles of the abdomen for the peristalsis that moves food through the digestive tract. In the other direction, when you are full from a meal, the gut sends signals to the brain to slow your body for rest, so that energy can be directed towards digestion. Unfortunately, sometimes this signaling system is thrown out of whack.
As scientists have delved deeper into the relationship between gut and brain, it has become clear that the diversity and abundance of certain microbial populations living within the gastrointestinal (GI) tract have significant influence on both the health of, and signaling between, the gut and brain. Because of this, a more accurate title for the phenomenon of gut-brain communication is the “microbiome-gut-brain axis”.
Microbiota influence the brain
An unhealthy or imbalanced gut microbiome (a condition also known as “dysbiosis”) can cause problems in the brain and changes to behavior, mood, and cognition. Compelling evidence for such an interaction was published almost 30 years ago when it was observed that a course of oral antibiotics resulted in dramatic mental improvement in patients with hepatic encephalopathy . Hepatic encephalopathy is characterized by neuropsychiatric abnormalities as a result of toxins from the gut entering the circulation. When antibiotics ended dysbiosis of the gut, however, a rapid change in neural effects soon followed, demonstrating an important relationship between changing microbial populations of the GI and brain function. Since then, data have been collected showing a potential role of microbiota in influencing anxiety and depression behaviors and even a link between dysbiosis and the severity of autism [2,3]. Normal brain development has been shown to be partially dependent on microbiotic presence in the gut, and animal studies suggest that social development also requires a certain level of health and balance in the GI microbiome [4,5].
The mechanisms of these relationships are still being elucidated through research. What is known is that the gut produces about 90% of the body’s serotonin, a neurotransmitter known to promote a sense of well-being. Bacteria living in the GI can induce enteric secretion of serotonin, along with other signaling molecules (such as dopamine, glutamine, and GABA) and activation of their receptors . The brains of research animals with altered or absent gut microbiota present various molecular differences including brain-region-specific changes in levels of brain-derived neurotrophic factor (BDNF), which is known to be modulated in anxiety and depression . Due to this evidence, healing dysbiosis and caring for your microbiome through diet and the use of probiotic and prebiotic fiber supplements are likely effective measures to support your mental health in combination with your digestion.
The brain influences microbiota
Conversely, psychological stress such as worry, fear, frustration, grief, and sadness can cause physiological changes that, in turn, alter the bacterial populations in our gut. Conditions such as irritable bowel syndrome (IBS) or stress-induced diarrhea can flush out beneficial bacterial species. As diet has the greatest effect on microbiotic health in the gut , eating more unhealthy comfort foods during times of stress can exacerbate dysbiotic conditions, worsening disrupted motility, reducing nutrient absorption, and even negatively affecting immune response. Over time these changes can lead to neurotransmitter imbalances and increased strain on our natural stress response.
When we experience stress, the sympathetic nervous system responds by engaging the body’s “fight or flight” mode. This deactivates signals for digestion, rest, or relaxation, as these physiological functions are not relevant to self-defense or fleeing from an emergency. These physiological changes are not meant to last very long. When stress becomes chronic, the digestive system becomes confused, and symptoms such as gas, bloating, nausea, reflux, or motility issues crop up. These symptoms are likely caused, at least in part, by changes to the microbiome responding to stress . Even events such as a social defeat or a reduction in social diversity have been documented to precede a change to GI microbial species known to affect neurotransmitter synthesis .
Healing and Maintaining a Healthy Microbiome
Knowing that the microorganisms living inside your gut can hurt or hinder your mental state along with your physical health is important. But it can be difficult to determine whether your unhealthy gut is the root of a low mood or anxiety, or your stress level is hurting the health of your gut. Either way, changing your diet and lifestyle to support healthy digestion will benefit your well being.
Animal studies involving microbiome manipulations have not only confirmed hypotheses about connections between gut populations and behavior, they have also shown that some of these effects can be corrected by supplementing with probiotics .
Taking a daily probiotic supplement is an efficient way to start improving the diversity and abundance of beneficial microbial species in the GI. While many fermented foods contain probiotic species, it is difficult for those probiotics to reach and populate the gut due to enzymes and stomach acids. A high-quality capsulated supplement on the other hand, such as BioMaintenance Shelf Stable Probiotic made by parent company Metabolic Maintenance, has been designed to withstand early stages of digestion to deliver maximum colony forming units (CFUs) of specifically selected beneficial bacteria and yeast strains directly to the intestine. As there are only so many adherence sites for bacteria in the walls of the gut, it may take some time for the beneficial strains to take root and begin to multiply, as pathogenic bacteria are slowly sloughed through natural bowel movement. This is why it is important to make a probiotic supplement part of your daily health regimen, rather than expecting one capsule to make a noticeable difference. You may start to notice a difference in physical symptoms of dysbiosis within as little as two days, but secondary benefits like mood may take a couple of months or more to notice a significant change [9,10]. Don’t give up! But do make sure you’re taking the right strains for your needs, a dose that is appropriate for your body condition, that your probiotic is from a trustworthy source, has not surpassed its expiration date, and that you are following that particular product’s instructions along with advice from your healthcare practitioner.
Another important piece to the probiotic puzzle is the amount of prebiotic fiber in your diet. As living organisms, probiotics need to eat. In order to survive and multiply, the microbial species that benefit the gut require oligosaccharides and fibers considered indigestible by the human gut. Pathogenic bacteria in the gut often thrive on sugar. Therefore, avoiding a high-sugar diet while taking a prebiotic supplement, such as the BioMaintenece Prebiotic + Fiber, is an effective way to nurture the growth and maintenance of desired bacterial species while ending the dominance of pathogenic species.
Food Intolerances and Sensitivities
If adding probiotics and prebiotics to your daily health regimen does not change uncomfortable GI symptoms over time, you benefit from a deeper analysis of your diet. While an allergic reaction to a food is likely to cause a histamine response such as a rash or sudden inflammation, a food sensitivity or intolerance is more likely to present as a GI issue (bloating, gas, diarrhea, etc.) and may be a bit more difficult to pinpoint. In some cases, the body isn’t producing enough natural enzymes for the abundance of certain food proteins being consumed. These proteins bypass digestion and are fermented in the gut causing uncomfortable, inconvenient, or even painful symptoms. Common intolerances include casein, lactose, and gluten. Taking a natural digestive aid, such as Metabolic Maintenance’s GluDaZyme can help break down these proteins (along with fats and other components) so that their nutritional value is absorbed, and fermentation (as well as its side effects) can be avoided. If the sensitivity is more serious, an elimination diet can help to determine the culprit so you know which foods to skip completely in the future.
Leaky gut is a different story. In order for absorption to occur, the intestinal wall acts as a sieve, allowing water and nutrients to move through the wall into the bloodstream. Toxins and undigested materials are too big to fit through, so they stay in the intestine, destined to be excreted from the body. Sometimes, the holes in the intestinal wall (called “tight junctions”) loosen, allowing toxins into the bloodstream along with nutrients and water. This phenomenon is called “leaky gut” or “intestinal hyperpermeability”. Leaky gut can cause symptoms throughout the body including inflammation and skin issues, confusion, and mood-related issues, and even lead to the development of more serious conditions such as diabetes and inflammatory bowel disease [11-14]. This condition can occur naturally, as some people are genetically predisposed to make more of a chemical called zonulin, which is responsible for loosening tight junctions. Gluten, however, can stimulate zonulin overproduction in some people who have an otherwise healthy gut, causing leaky gut syndrome .
Gluten is not the only potential cause of leaky gut. There are certain bacteria that also stimulate the overproduction of zonulin, and alcohol and refined sugar have also been linked with the permeability of tight junctions [15-17]. If you think you may be suffering from a leaky gut, your doctor will likely recommend some combination of a low FODMAP diet, pre- and probiotics, and self-care behaviors to destress your system to heal your gut.
This editorial mentions products manufactured by the parent company of MethylPro, Metabolic Maintenance. Metabolic has been an industry leader of professional supplements used and recommended by practitioners for over 35 years. Metabolic Maintenance manufactures both brands and offers them direct to consumers through their respective websites. For more information on the brand relationship and additional high quality nutritional supplement offerings, please visit: www.metabolicmaintenance.com
- Morgan, M. Y. “The treatment of chronic hepatic encephalopathy.” Hepato-gastroenterology 38.5 (1991): 377-387.
- Foster, Jane A., and Karen-Anne McVey Neufeld. “Gut–brain axis: how the microbiome influences anxiety and depression.” Trends in neurosciences 36.5 (2013): 305-312.
- Mayer, Emeran A., David Padua, and Kirsten Tillisch. “Altered brain‐gut axis in autism: comorbidity or causative mechanisms?.” Bioessays 36.10 (2014): 933-939.
- Desbonnet, Lieve, et al. “Microbiota is essential for social development in the mouse.” Molecular psychiatry 19.2 (2014): 146-148.
- Stilling, Roman M., et al. “Microbes & neurodevelopment–Absence of microbiota during early life increases activity-related transcriptional pathways in the amygdala.” Brain, behavior, and immunity 50 (2015): 209-220.
- De Vadder, Filipe, et al. “Gut microbiota regulates maturation of the adult enteric nervous system via enteric serotonin networks.” Proceedings of the National Academy of Sciences 115.25 (2018): 6458-6463.
- Bray, Natasha. “The Microbiota-brain-gut Axis.” Nature Research. June 2019. https://www.nature.com/articles/d42859-019-00021-3
- Foster, Jane A., Linda Rinaman, and John F. Cryan. “Stress & the gut-brain axis: regulation by the microbiome.” Neurobiology of stress 7 (2017): 124-136.
- Allen, Stephen J., et al. “Probiotics for treating acute infectious diarrhoea.” Cochrane Database of Systematic Reviews 11 (2010).
- Choi, Chang Hwan, et al. “A randomized, double-blind, placebo-controlled multicenter trial of Saccharomyces boulardii in irritable bowel syndrome: effect on quality of life.” Journal of clinical gastroenterology 45.8 (2011): 679-683.
- Arrieta, Marie-Claire, Lana Bistritz, and J. B. Meddings. “Alterations in intestinal permeability.” Gut 55.10 (2006): 1512-1520.
- Eske, Jamie. “What to know about leaky gut syndrome”. Medical News Today. August 21, 2019. https://www.medicalnewstoday.com/articles/326117
- Peters, Anneli, and Hartmut Wekerle. “Autoimmune diabetes mellitus and the leaky gut.” Proceedings of the National Academy of Sciences 116.30 (2019): 14788-14790.
- Lee, Sung Hee. “Intestinal permeability regulation by tight junction: implication on inflammatory bowel diseases.” Intestinal research 13.1 (2015): 11.
- Fasano, Alessio. “Intestinal permeability and its regulation by zonulin: diagnostic and therapeutic implications.” Clinical Gastroenterology and Hepatology 10.10 (2012): 1096-1100.
- Wang, Ying, et al. “Effects of alcohol on intestinal epithelial barrier permeability and expression of tight junction‑associated proteins.” Molecular medicine reports 9.6 (2014): 2352-2356.
- Bischoff, Stephan C., et al. “Intestinal permeability–a new target for disease prevention and therapy.” BMC gastroenterology 14.1 (2014): 189.