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Understanding Chronic or Functional Diarrhea

What is Diarrhea?

Diarrhea is defined as passing frequent and/or loose or watery stools. Acute diarrhea goes away in a few weeks, and becomes chronic when it lasts longer than 3–4 weeks. If no specific cause is found after a thorough investigation and certain criteria are met, a diagnosis of functional or chronic diarrhea may be considered.

What are Functional Bowel Disorders?

People with functional diarrhea of other functional bowel disorders do not demonstrate physical or laboratory abnormalities to explain their gastrointestinal (GI) symptoms. One example of a functional bowel disorder is irritable bowel syndrome (IBS), which is estimated to affect approximately 10–15% of all adults.

Learn more about IBS

Is Functional Diarrhea the Same as Irritable Bowel Syndrome?

Individuals with functional diarrhea may represent a subgroup of people with IBS. People with IBS often report altered bowel habits, including diarrhea and/or constipation, associated with abdominal pain. Bloating, feeling an urgent need to use a bathroom, straining, or a sense of incomplete evacuation may also occur.  Many of these symptoms occur in persons with functional diarrhea but the absence of abdominal pain distinguishes these people from those with IBS.

How do Doctors Evaluate Patients with Functional Diarrhea?

The doctor will begin with asking about your medical history, including use of medicines and dietary habits, and performing a careful physical examination. Additional studies such as blood tests and stool analysis may be ordered.

Diagnostic procedures such as colonoscopy or endoscopy may be indicated, allowing the physician to examine the inner surface of the colon and small intestine to exclude other causes of chronic diarrhea, such as infections or inflammation of the colon or small intestinal diseases.

Why is the Medical and Dietary History so Important?

A diagnosis of functional diarrhea is made only after other possible causes, such as medications and diet induced diarrhea, are excluded. The list of medications which cause diarrhea is extensive and includes certain antibiotics, magnesium containing antacids, blood pressure lowering agents (including beta-blockers, ACE inhibitors), and drugs to control irregular heart beat (quinidine). All medications, whether prescription or over the counter, should be brought to the attention of the physician.

Although some people are sensitive to wheat and other related grains (Celiac disease, gluten enteropathy), true food allergies are rare. However, inability to completely absorb certain food groups can, if they are eaten in sufficient quantities, lead to diarrhea in some people. Milk (lactose) intolerance is one of the more common examples of this.

People with lactose intolerance have low levels of intestinal lactase, the enzyme required to digest the milk sugar, lactose. The unabsorbed sugar then passes to the colon where it is broken down by bacteria to produce abdominal gas (bloating) and diarrhea. Whether a person develops symptoms depends on many factors including the amount of lactose ingested and the levels of lactase enzyme in the small intestine.

Treatment involves reducing or eliminating lactose in the diet or using commercial products that contain the lactase enzyme. Other persons are intolerant of fructose (found in fruit and fruit juices), sorbitol (plums, pears and sugarless gum), and caffeine (coffee, tea, many sodas). Dietary elimination of possible offending agents may resolve symptoms in sensitive persons.

What Other Factors May Worsen Functional Diarrhea?

Some people develop diarrhea after undergoing stomach or gallbladder surgery. The exact mechanisms are unclear, but are thought to involve increased transport of food through the GI tract or an increase in bile salts delivered to the colon.

A condition called “runner’s diarrhea” has been described. As the name suggests, these individuals experience diarrhea during long distance marathons.  The cause is uncertain but may involve alterations of GI motor activity.

What is the Cause of Functional Diarrhea?

Although there is no consensus, one proposed mechanism relates to alterations in gastrointestinal motility. Contractions of the smooth muscle of the GI tract regulate movement of food through the small intestine and colon.

People with functional diarrhea may have different motility patterns than do people without diarrhea. However, the causes of the motility dysfunction and changes in intestinal fluid absorption leading to firmer stools or to diarrhea are incompletely understood.

What Treatments are Available for Functional Diarrhea?

As the cause of functional diarrhea is unknown, treatment is aimed at symptoms. Dietary modifications include elimination of various substances known to cause diarrhea. In addition to lactose, fructose, sorbitol, and caffeine some persons develop symptoms because they do not completely digest complex carbohydrates (pasta, beans). These too may be reduced in the diet to see if there is any improvement.

Some people with IBS and diarrhea may benefit from an increase in dietary fiber. In contrast, other people benefit from carbohydrate restriction.

For people who do not improve with dietary modifications, antidiarrheal agents such as loperamide (Imodium) or diphenoxylate (Lomotil) are often effective. All work by similar mechanisms. In general, these drugs are used under the supervision of a physician; diphenoxylate requires a doctor’s prescription.

As future research uncovers the mechanisms which underlie functional diarrhea, more specific therapies will be developed. As with many functional disorders, an effective physician-patient relationship should enhance the treatment of this complex problem and promote a better understanding of the dynamics of GI symptoms.

Patient Perspective on Chronic Diarrhea

Listen to a patient perspective on living with chronic diarrhea related to a gastrointestinal (GI) disorder.

Adapted from “Functional Diarrhea- Some Answers to Often Asked Questions”– IFFGD publication #105 by Arnold Wald, MD, MACG, AGAF, University of Wisconsin School of Medicine and Public Health, Madison, WI

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IFFGD is a nonprofit education and research organization. Our mission is to inform, assist, and support people affected by gastrointestinal disorders.

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