Digestive System Facts: What Do the Different Colors of Stool Mean?

Whether you have eaten meat, bread, beans, broccoli, or carrots, the waste that the body excretes in the stool inevitably turns brown in most cases.

Toilet Paper

Toilet Paper

Where does the coloration of human feces come from? And why can stool sometimes be black, yellow, silver, red, purple, or orange?

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75% of the volume of a normal bowel movement is water. The 25% is a mixture of food residue, undigested food particles (especially plant fiber), dead and live bacteria, and other substances produced by the liver and intestines.
The brown color of the stool is mainly due to the breakdown of red blood cells. Our body excretes millions of red blood cells per day, which are first converted into biliverdin (green) and then into bilirubin (yellow), which mixes with bile in the liver. Under the action of bacteria in the intestines, bilirubin is further metabolized to stercobilin (brown in color), which gives the stool its brown color. The body excretes between 150-250 mg of this pigment each day.

Black, green, or yellow stools: what does it mean?

Although stool is usually brown, several factors can still affect its color.

Yellow stool: this color, combined with a foul odor, maybe a sign of poor fat absorption due to pancreatic malfunction. It may also be caused by giardiasis a parasite that causes an infection of the intestinal tract. Celiac disease, Gilbert’s syndrome, stress, and diet may also cause yellow stool.

Gray or pale: a sign that bilirubin is no longer reaching the intestines, where it turns brown. This can be related to any disease that causes obstruction of the bile ducts (cancer, gallstones, inflammatory diseases, and hepatitis).

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Black stool: indicates the presence of red blood cells that have not been broken down and digested, which may indicate internal bleeding from the upper digestive tract, especially if the stool has a foul odor. Ingestion of iron, licorice, and other dark foods may also cause blackening of the stool.

Bright Red stool: indicates bleeding in the lower digestive tract due to inflammatory bowel disease, diverticulitis, polyps, anal fissures, or hemorrhoids.

Blue stool: may be caused by products used to treat radiation poisoning (cesium, and thallium) or colorings found in soft drinks as would be the case in grape soda.

Silver stool: maybe the sign of both gastrointestinal bleeding and biliary obstruction.

Green, purple or orange stools: these colors are most commonly associated with eating large amounts of highly colored foods such as beets, carrots, spinach, squash, and sweet potatoes. Supplementation with beta-carotene turns stools orange, and supplementation with iron sometimes turns them green.

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If the change in stool color is accompanied by a change in consistency such as in the case of diarrhea or with other symptoms, see your doctor immediately for further evaluation.


An objective measure of stool color for differentiating upper from lower gastrointestinal bleeding

Application of 2D fluorescence spectroscopy on faecal pigments in water



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