Irritable Bowel Syndrome (IBS)

IBS is a common functional disorder of the large intestine that affects an estimated 20% of the global population, with a significant negative impact on quality of life and high co-occurrence with anxiety and depression.^[1] IBS is twice as common in women compared to men, which could be explained, in part, by genetics and hormonal changes during the menstrual cycle.^[2]

IBS can be classified into three different subtypes: diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), or mixed (IBS-M). If it occurs after a gastrointestinal infection, such as food poisoning, it’s considered post-infectious IBS.^[3]

The main signs and symptoms of IBS include long-term changes in bowel habits (lasting months), abdominal pain, bloating, mucus in the stool, and a feeling of incomplete evacuation after having a bowel movement.^[3]

The Rome IV criteria can be used to diagnose IBS based on the proportion of bowel movements rated as constipation or diarrhea compared to those rated as normal. Symptoms need to occur at least once per week for at least three months to be considered IBS.^[4] However, there is no exact test for IBS, so a doctor (often a gastroenterologist) may need to rule out other potential diseases with blood and stool tests, and they might also perform a colonoscopy.^[3]

Medications for diarrhea-predominant IBS include antidiarrheals that reduce intestinal motility (organized contractions of the digestive tract) and reduce water content in the bowel. Doctors may also prescribe antibiotics to treat underlying infections or small intestinal bacterial overgrowth (SIBO). Drugs for constipation include over-the-counter laxatives or prescriptions that increase water content in the bowel or enhance intestinal motility. Antidepressants or antispasmodics can be used to normalize intestinal motility.^[3]

Several supplements have been studied and supported by strong evidence for the relief of certain IBS symptoms. Enteric-coated peppermint oil can reduce abdominal pain, and certain probiotic strains are effective for multi-symptom relief.^[5][6] Polymethylsiloxane polyhydrate — an over-the-counter intestinal adsorbent — may also relieve multiple IBS symptoms.^[7] One study has shown that glutamine supplementation may improve the symptoms of post-infectious IBS.^[8] Prebiotics (carbohydrates used preferentially by beneficial gut microbes) aren’t clearly effective, however, and the benefits of other alternatives like traditional Chinese medicinal herbs or aloe vera need to be confirmed in higher-quality studies.^[9]

Many soluble fibers can be fermented by gut microbes to produce energy, resulting in by-products such as short-chain fatty acids and gas. The combination of fermentability and solubility can lead to accumulated gas and water retention in the colon, which can worsen abdominal pain and diarrhea. The low-FODMAP diet has been shown to reduce diarrhea-predominant IBS symptoms, and traditional dietary advice (such as avoiding trigger foods, limiting alcohol, and eating smaller, more frequent meals) is similarly effective.^[10]

Cognitive behavioral therapy provided modest IBS symptom improvement (similar to other forms of psychotherapy) in a small number of studies.^[11] Hypnotherapy has also been found to help about 50% of the participants in the few studies that have been performed.^[12] Psyllium husk is an over-the-counter fiber supplement that can normalize stool and reduce symptoms in IBS.^[13] Acupuncture has also been studied, but it was no more effective than the sham (or placebo) treatment, so its benefits are very likely due to the placebo effect.^[14]

The causes of IBS are unknown, but research indicates a number of factors are involved, including abnormal gut-brain axis communication, visceral hypersensitivity and altered motility, and the gut microbiota. Miscommunication between the brain and the gut could cause abnormal intestinal motility and visceral hypersensitivity, leading to changes in bowel function and abdominal pain. One form of IBS can be brought on by a gastrointestinal infection, and many symptoms of IBS also occur with small-intestinal bacterial overgrowth (SIBO). Some studies show that the gut microbes of people with IBS differ from healthy people, but it’s unclear whether this is a cause or a consequence of the disease. Genetics and early life trauma may also influence the risk of developing IBS later in life.^[3]