Three-quarters of your poop consists of water and most of the rest is food your body didn’t digest.
Once it exits the digestive system, poop is usually a shade of brown, regardless of the appearance of whatever you’ve had to eat and drink, because it contains a chemical your body makes.
That chemical, stercobilin, is a product of the breakdown of hemoglobin – an iron-containing protein in red blood cells that allows oxygen to be transported around the body. Without sercobilin, your poop would probably look pale or even white. That’s because most of the chemicals that give food many different colors are completely broken down in the digestive process.
Bilirubin eventually makes its way to the liver through the circulatory system and is modified and then secreted into the small intestine by the liver in the form of bile. Bile, a yellow-green fluid, helps your body digest and absorb fats. While your body does absorb and reuse some bilirubin as the food you’re digesting moves through the small intestine, the rest of that bilirubin becomes stercobilin – which your body must dispose of.
And that stercobilin gets combined with the stuff you’re digesting, making your poop brown by the time it exits your body.
Poop, of course, isn’t always brown. It can be a different color, depending on what you eat and how fast the stuff moves through your system.
When poop moves too quickly through your body, the bilirubin in the bile does not have enough time to be broken down to form stercobilin, which would make it browner.
If you eat a lot of something, especially if it’s hard for your body to quickly digest, your poop may look funny. For some people, eating beets leads to red poop or reddish urine.
Your body can’t possibly absorb everything that you eat and drink. Some foods, like corn kernels, can’t be fully digested by people. They may even come out in poop looking the same size and color as when you ate them.
Even though it may seem gross, I recommend that you regularly peek at your poop before flushing to make sure it’s brown and squishy. If most of it is an unusual color, such as black or white, it could be a sign you need to see a doctor. The same goes for having poop that is too hard or too runny. If your poop is red and you haven’t been eating beets, that might also be cause for concern.
Written by Hannibal Person, Assistant Professor of Gastroenterology and Hepatology, School of Medicine, University of Washington.
This article was first published in The Conversation.