The Role of Serotonin in Irritable Bowel Syndrome (IBS)
Updated: May 1
What is Irritable bowel syndrome (IBS)?
Irritable bowel syndrome (IBS) is a digestive condition where the bowel function is altered and people who suffer from it can experience diarrhea, constipation or sometimes both. IBS is classified based on which symptom is predominant: IBS-D (diarrhea), IBS-C (constipation) or IBS-M (mixed). Other symptoms include cramping, abdominal pain, gas, bloating, urgency to have a bowel movement and changes in mood. To understand why these symptoms occur, we need to talk about a neurotransmitter called serotonin that influences both the activity of the brain and the digestive system.
Serotonin and IBS
Serotonin or 5-HT (5-hydroxytryptamine) is a substance that is secreted by the cells lining our intestines. It controls the intestinal contractions that move digested food through the intestines, the secretion of digestive enzymes and how our brain interprets pain signals coming from our gut.
Being a neurotransmitter, serotonin is present in the brain, but 95% of it is found in the gut because it plays such an important role in our intestinal function. In our brain, serotonin affects our mood and feelings of contentment, patience, satiety, anxiety, and depression.
Serotonin plays a significant role in IBS. Serotonin has a transporter in the intestinal wall that determines how long it stays around and has effects. People with IBS-D have less of these transporters, which means serotonin stays around in the gut longer to stimulate intestinal contractions, resulting in cramping and diarrhea. Individuals with IBS-C may have too many of these transporters, meaning serotonin isn't allowed to stay around and stimulate the gut, resulting in low motility and constipation.
Serotonin also controls our perception of pain. When there is bloating, cramping and pain in the abdomen the brain will usually send signals to the gut to down-regulate the sensation. However, in IBS, this down-regulation doesn’t happen and those with the disease are very sensitive to bloating and the abdominal pain it causes.
Serotonin and the gut-brain connection
A healthy microbiome is important for serotonin metabolism. The microbiome are the good and bad bacteria that live in your digestive system. You have many different species of bacteria that live in your mouth, stomach, and intestines. The type of bacteria differ depending on where they're located and what the environment is like.
Mental health conditions like depression and anxiety, as well as learning, memory and cognitive function can be influenced by our gut bacteria. It's thought that the vagus nerve, which runs from the brain to the digestive system, is responsible for this gut-brain connection.
Microbes can influence the production and activity of serotonin. The microbes tell the intestinal cells to produce and release serotonin and control how much serotonin is active in the gut by regulating the activity of the transporter. The amino acid tryptophan, which is a precursor to serotonin, is also influenced by our good bacteria.
A substance called butyrate, made by our bacteria, also plays a role in IBS. When we have a wide array of beneficial bacteria in our microbiome they make this substance, which is the preferred energy source for our intestinal cells. Butyrate acts as an anti-inflammatory and influences bowel motility and our brain's hypersensitivity to pain.
These beneficial effects from healthy gut flora may explain why a healthy diet, prebiotics and probiotics are a treatment strategy used by many naturopathic doctors to treat IBS.
General naturopathic approaches to IBS
Dietary fiber from fruits and vegetables
Eliminating allergic or intolerant foods from the diet
Eliminating sugar from the diet
Stress management techniques such as meditation/deep breathing, yoga, exercise
Probiotics for gut health
Following a low-FODMAP diet that limits carbohydrates to reduce gas and bloating
Enteric coated peppermint for gas and bloating
Irritable bowel syndrome (IBS) is a digestive condition involving diarrhea, constipation, cramping, abdominal pain, gas, bloating, urgency to have a bowel movement and changes in mood. Serotonin or 5-HT (5-hydroxytryptamine) is a substance that is secreted by the cells lining our intestines and controls intestinal motility, the secretion of digestive enzymes and how our brain interprets abdominal pain signals. The serotonin transporter, found in the lining of the intestines, regulates how much serotonin is present in the gut. People with IBS-D have less of these transporters and individuals with IBS-C may have too many of these transporters. A healthy microbiome is important for serotonin metabolism and microbes influence the production and activity of serotonin through the serotonin transporter and metabolism of tryptophan. Butyrate, made by our beneficial bacteria, is significant in IBS because it acts as an anti-inflammatory and influences bowel motility and our brain's hypersensitivity to pain. General naturopathic approaches to IBS include fiber, eliminating sugar and allergic foods, stress management, probiotics, a low-FODMAP diet and peppermint.
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“IBS and Serotonin.” Gastrointestinal Society, Canadian Society of Intestinal Research, 2004, badgut.org/information-centre/a-z-digestive-topics/ibs-and-serotonin/.
Jin, Duo-Chen, et al. “Regulation of the Serotonin Transporter in the Pathogenesis of Irritable Bowel Syndrome.” World Journal of Gastroenterology, Baishideng Publishing Group Inc, 28 Sept. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC5037082/.
Rogers, G B, et al. “From Gut Dysbiosis to Altered Brain Function and Mental Illness: Mechanisms and Pathways.” Nature News, Nature Publishing Group, 19 Apr. 2016, www.nature.com/articles/mp201650.
Załęski, Andrzej, et al. “Butyric Acid in Irritable Bowel Syndrome.” Gastroenterology Review, Termedia Publishing House, 2013, www.ncbi.nlm.nih.gov/pmc/articles/PMC4027835/.
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