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What Causes Gas and Loose Stools?

author image Dr. Tina M. St. John
Tina M. St. John runs a health communications and consulting firm. She is also an author and editor, and was formerly a senior medical officer with the U.S. Centers for Disease Control and Prevention. St. John holds an M.D. from Emory University School of Medicine.
What Causes Gas and Loose Stools?
A woman is laying on the couch with stomach pain. Photo Credit Wavebreakmedia Ltd/Wavebreak Media/Getty Images


Intestinal gas and loose stools often occur simultaneously with a variety of disorders and conditions. Incomplete digestion commonly leads to diarrhea. As undigested food reaches the large intestine, colonic bacteria break down the particles, producing gas. Functional disorders of the colon can also affect the consistency of stool and the production of gas. As many disorders can cause gas and loose stools, an accurate diagnosis proves pivotal in devising an effective treatment strategy.

Irritable Bowel Syndrome

Irritable bowel syndrome is a disorder characterized by intermittent abdominal pain, discomfort or cramps that is accompanied by gas, bloating and loose stools or constipation. The National Institute of Diabetes and Digestive and Kidney Diseases estimates that roughly 20 percent of the population in the United States has occasional symptoms of irritable bowel syndrome.

The disorder disproportionately affects women. While the triggering mechanisms that lead to irritable bowel syndrome remain an area of active medical research, it's clear that muscular hyperactivity of the colon leads to loose stools. Certain foods may increase irritable bowel syndrome symptoms, including caffeinated tea, coffee and soda, large meals, chocolate, alcohol, dairy products, rye, barley and wheat.

Excessive stress and emotional upset may also precipitate irritable bowel syndrome symptoms. The condition is not life threatening and is not associated with an increased risk for ulcerative colitis, Crohn disease or colorectal cancer.

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Lactose Intolerance

A low concentration of the enzyme lactase in the small intestine causes lactose intolerance. Lactose, or milk sugar, is too large to be absorbed by the small intestine. The enzyme lactase breaks down lactose into smaller sugar molecules, facilitating intestinal absorption.

Many people experience a decrease in lactase production as they reach late adolescence and adulthood. When the amount of milk and dairy products consumed overwhelms the available lactase in the small intestine, undigested lactose causes intestinal symptoms, or lactose intolerance.

Symptoms include abdominal cramps, intestinal gas and loose stools. The National Institute of Diabetes and Digestive and Kidney Diseases reports that lactose intolerance occurs more commonly in African, Asian and Hispanic Americans compared to those of European descent. The disorder is uncommon in children.

Pancreatic Insufficiency

Disorders that adversely affect the digestion of dietary nutrients can lead to loose stools and gas. The pancreas produces the overwhelming majority of the digestive enzymes in the intestine. Proteases, amylases and lipases break down proteins, starches and fats, respectively.

Deficient production or release of pancreatic digestive enzymes leaves large quantities of undigested food in the small and large intestine. The undigested food precipitates increased amounts of intestinal gas and diarrhea.

The medical reference text "Harrison’s Principles of Medicine" notes that possible causes of pancreatic insufficiency include chronic pancreatitis, pancreatic tumors, abdominal radiation therapy, cystic fibrosis, hemochromatosis, alpha-1-antitrypsin deficiency and Shwachman-Diamond syndrome.

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