Poop’s pigmentation is the product of more than diets and digestion
As anyone with diaper-changing experience knows, even a quick glance at someone’s poop can reveal a lot about a person. The presence of a bit of corn kernel or hue of, ugh, blueberries would seem to tell the whole picture. Look more closely (figuratively!) at the situation, and you’ll realize that there’s more to a poop’s appearance than its creator’s last meal. Some fecal features actually owe a lot to the specifics of the anatomy that produced them, as well as what raw materials were involved in the process.
Dyed by diets
The core ingredients of most poop is a combination of water, indigestible materials like fiber, and other organic materials, like dead cells and bacteria. Dietary specifics can then modify that base, such as removing the fiber and adding more blood to give you the dark red, smooth feces of something like a bedbug. Butterflies, appropriately, only release a spray of clear liquid that’s almost pure water, with only a hint of fairy dust. However, this concept doesn’t mean that birds live on a diet of cream or egg whites, because that coloration is due to their pee.
Birds, and many reptiles, handle all incoming and outgoing substances through either their mouth or an orifice called the cloaca. The cloaca is located where you’d generally locate an anus, but is the sort of catch-all opening for reproductive and digestive transmissions, meaning that everything from eggs to urine can pass through there. This doesn’t mean that these animals actually blend these systems in their bodies— birds and lizards still have distinct stomachs and bladders and everything, it’s just that because they share the same exit, they’re likely to get blended together on their way out. When a bird expels waste, the pee and poo gets mixed together, and uric acid in the pee reacts with ingredients in the poop that gives you that telltale white goop you find on your car’s windshield. Any darker bits you see in bird poo is the actual feces that just hasn’t reacted with the uric acid yet.
Brown is best
Human poop would also be a chalky gray or white, if not for the addition of an orange-brown compound called bilirubin, which is excreted by the liver. When mixed with yellowish bile, you get the delightful brown color we all know and love. There’s obviously some variability in poop’s coloration, but staying within the umber to maybe yellow ochre range may be important, as pronounced color shifts can actually hint at serious health problems. Too much green could mean too much bacteria, yellow an imbalance of fats, and deep red can be a sign of internal bleeding. So unless you know your diet has been especially colorful lately, it’s probably best to enjoy the browns your liver cooks up for you.
Source: Why Poop Is Brown by Daven Hiskey, Today I Found Out