The odor of stool comes from bacterial fermentation in fecal matter, which is 75-85% water and about 20% dry matter. But why the brown color? Let's explore.
Stool typically appears brown after passing through the digestive system, regardless of your recent diet. This hue comes from stercobilin, a byproduct of hemoglobin breakdown. Hemoglobin, the iron-rich protein in red blood cells, transports oxygen throughout the body.
As hemoglobin degrades, it forms bilirubin, a yellow pigment. Bilirubin travels via the bloodstream to the liver, where it's processed and secreted into the small intestine as part of bile. Bile aids fat digestion and absorption; the remainder converts to stercobilin, which is excreted.
This bile-derived pigment mixes with water from digested food remnants, giving stool its brown color. Without stercobilin, stools would appear pale, as most food pigments break down completely during digestion.
Though not glamorous, stool analysis is a key medical tool for detecting diseases based on shape, color, and texture (see this infographic for details).
Researchers are advancing rapid stool analysis. At Duke University, experts presented a prototype at Digestive Disease Week® (DDW) that images stool in toilet pipes for analysis, potentially tracking chronic gastrointestinal issues.
Stanford University is developing similar tech, including urine dipsticks to detect molecular markers for conditions like urinary tract infections and bladder cancer.
