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Diet and Nutrition

The color of stool and diet

06/22/1998

Question:

What does dark stool indicate in one's diet?

Answer:

A number of medical and nutritional factors can affect the appearance of stool. In a healthy individual, stool is a light to dark brown color. This coloration is caused by bile pigments, byproducts of a substance the liver secretes into the intestine in order to be able to absorb fatty nutrients.

An abnormal-appearing stool can be a warning sign of a serious condition. Blood in the stool is a common problem which can be caused by something as simple as a hemorrhoid or can be a sign of a more dangerous illness such as cancer. Blood that arises from the lowest parts of the colon or the rectum appears red or maroon, as you would expect. On the other hand, bleeding from a source higher up in the digestive tract such as the right side of the colon or the stomach and duodenum looks black. A few medications, such as iron tablets and bismuth (one of the key ingredients in Pepto-Bismol), can also turn the stool black. Unless you are taking one of these medications, a black, tarry appearing stool should prompt you to contact your doctor.

Blood in the stool is an important clue to diseases of the digestive tract. Unfortunately, blood cannot always be detected in stool with the naked eye. For this reason, there are special tests which perform a simple chemical test to check for blood. This is often referred to as fecal occult (hidden) blood screening. Your doctor can test for occult blood during an examination of your rectum or send a patient home with a kit for testing for occult blood.

Very pale stools (white clay colored) occur when bile is not secreted into the colon. This condition occurs in some gallbladder and liver conditions.

A stool which is pale and greasy-appearing is seen with steatorrhea - a condition in which the body is unable to absorb fats and other important nutrients.

Several foods can affect the color of stool. Beets, red peppers and foods with red coloring, when eaten in large amounts, can turn the stool red. The test used in occult blood testing can distinguish this dietary cause from blood in the stool if a question should arise.

Reference: Fecal Analysis in Bockus Gastroenterology, 1985 Ed by Berk, JE

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Response by:

Jill Foster, MD
Formerly, Assistant Professor
College of Medicine
University of Cincinnati