Diarrhea Predominant Irritable Bowel Syndrome (IBS-D)

IBS-D is a subtype of IBS characterized by abdominal pain, gas, bloating, and frequent, urgent diarrhea. Approximately 29% of IBS sufferers have IBS-D, and women are more commonly affected than men.^[1]

IBS-D shares most symptoms — including abdominal pain, bloating, and gas — with the other IBS subtypes, but in IBS-D, diarrhea is the predominant bowel habit. People with IBS-D also report more abdominal pain compared to the other subtypes.^[2]

Symptoms often subside after a bowel movement, but will sometimes worsen after certain triggers such as caffeine, psychological stress, and foods high in certain fermentable carbohydrates (e.g., beans and wheat products; see Low-Fodmap Diet).^[3]

There is no test to diagnose IBS-D, so doctors often use blood and stool tests to rule out other diseases before reaching an IBS-D diagnosis. Rome IV criteria can be used to diagnose IBS-D based on the proportion of bowel movements rated as diarrhea compared to those rated as normal.^[4] Symptoms need to occur at least once per week for at least three months to be considered IBS.^[3]

Medications for IBS-D broadly include antidiarrheals, antispasmodics, and antidepressants. They work by reducing or normalizing intestinal motility (organized contractions of the digestive tract) and water content in the bowel. In some cases, antibiotics are prescribed to treat an underlying infection or small intestinal bacterial overgrowth (SIBO).^[3]

Few supplements have been studied for IBS-D specifically, but enteric-coated peppermint oil can reduce abdominal pain and certain probiotic strains are effective for multi-symptom relief.^[5][6]

In a 16-week placebo controlled trial (including an 8-week double-blind phase followed by an 8-week open label phase), polymethylsiloxane polyhydrate — an over-the-counter intestinal absorbent — improved abdominal pain, stool consistency, and the frequency and urgency of bowel movements in IBS-D.^[2]

Certain foods and substances, including caffeine, sugar alcohols, and some types of dietary fiber, can worsen IBS-D symptoms by increasing gut motility or retaining fluid in the intestines. These factors explain, in part, why a low-FODMAP diet is recommended for people with IBS-D.

In a 12-week randomized controlled trial, researchers compared a low-FODMAP diet to one that replaced cereal grains (like wheat) with Tritordeum (a hybrid of durum wheat and wild barley), and found that both diets were equally effective at reducing IBS-D symptoms.^[7]

Traditional dietary advice — such as avoiding trigger foods, limiting alcohol, and eating smaller, more frequent meals — is also effective (though the low-FODMAP diet is slightly more effective.)^[8][3]

Moxibustion — which involves heating different areas of the body with burning mugwort leaves — was found in one meta-analysis to be superior to medication for improving bloating and bowel movement frequency in IBS-D, but with a high risk of bias due to the lack of blinding in nearly all studies.^[9] Tong Xie Yao Fang, a traditional Chinese medicine formula, was also reported to be superior to conventional treatment in another meta-analysis that also cited a high risk of bias due to the lack of blinding and randomization.^[10] Shugan Jianpi Zhixie (an ingredient of Tong Xie Yao Fang) was more effective than placebo according to one meta-analysis that only included randomized, double-blind, placebo-controlled trials, but it wasn’t compared to conventional treatment.^[11]

Though the cause of IBS-D is still unknown, research suggests that multiple factors — such as the gut-brain axis, abnormal muscular contractions, gut microbes, hormones and genetics — could play a role in the disease.

IBS is twice as common in women compared to men, which could be explained, in part, by hormonal changes during the menstrual cycle.^[12] Other evidence suggests that some women with IBS-D carry a gene mutation that affects their gut-derived serotonin receptors, which could lead to abnormal motility.^[1][3]