Science Question from a Toddler: Why is poop brown?


Two Science Questions from a Toddler in the same month? It's a Festivus miracle! Or, you know, the unexpected byproduct of trying to write weekly blog posts during a month where damn-near all the sources you need to talk to are on vacation. But I'm a glass is half-full kind of woman.

Speaking of byproducts, BB reader Tammy says there's a small person in her life who wants to know, "Why is poop brown?"

First off, the fact that this kid's poop is brown is a really good sign. See, your stool can come in several different colors. Brown just happens to be the color of good health.

"Bile comes from your gall bladder and helps your body digest food," said Anish Sheth, M.D., assistant professor at Yale Medical School and author of the book What's Your Poo Telling You? "It's metabolized by the bacteria in your large intestine, leaving behind a byproduct called stercobilin—and it's that stercobilin that gives stool a brown pigment."

Without stercobilin, your poo would actually be a sort of pale, off-grey color, like white clay. This really does happen from time to time, Dr. Sheth said, when something is blocking a patient's bile duct, so that bile can't get from the gall bladder into the intestinal tract. The cause could be as simple as a gall stone, or as ominous as pancreatic cancer.

In fact, the color of poop can offer some surprising insights into what's going on with the human body. In the days before fancy medical technology, doctors looked at the color and texture of poop to help diagnose gastro-intestinal illness. Today, changes in stool are still frequently the first sign that something is wrong. There's three main "wrong colors" your poop can be:

While I had Dr. Sheth on the line, I decided that I had to ask him the ultimate "Why does my poop look like that" question. Oh yes, I asked about corn.

"There are a lot of things that we can't fully digest. I call it 'Deja Poo'. Corn is just the most common example," Dr. Sheth said.

The key is fiber. There's two kinds: Soluble and insoluble. If what you eat has a lot of insoluble fiber, it'll come out your other end mostly intact, because your body can't digest it. The foods that contain insoluble fiber foods are almost all plants, Dr. Sheth said, because humans haven't evolved the enzymes necessary to break down some plant cell walls. In the case of corn, some of the plant is soluble fiber and some isn't.

"There's two parts of the corn—the exterior kernel that we pass through and the germ inside of it. The germ is actually extracted. The whole kernel is immersed in digestive enzymes and your body pulls out what it can use," Dr. Sheth said. "What it can't use just passes on."

Ask Dr. Sheth your poop-related questions at his Web site, Dr. Stool

Image courtesy Flickr user GregtheBusker, via CC