I usually look at my poo after I go, and I've noticed it's often different colors. Last night it was a beautiful emerald green. What's up with all the weird colors, and do they mean anything medically? — Thomas K., Secaucus, NJ
Bowel movements are endlessly fascinating to some people. For some it's regularity: if they don't go on some kind of schedule, they worry about it. For others, it's consistency: a nice, massive dump makes them happy but a hard or watery defecation is cause for concern. There's no question bowel movements are important; if you go long enough without going, it'll make you miserable, and can even become a medical emergency. One of the things people don't regularly pay attention to is the color of their stool, but it can say a lot about what's going on inside.
Turds are generally brownish in color, due to a chemical called stercobilinogen (that's a good factoid for trivia night, by the way) which is basically broken down bile from the gallbladder. The logs themselves are made up of indigestible things (fiber, corn husks, etc.), dead bacteria, and water. Different environmental factors can change the color of your choads, though, as I'll outline below.
Blood (from bleeding anywhere in or above the stomach) is partially digested and turns stool into a black, tarry mess that is called "melena" in the medical profession. These stools demand an immediate medical evaluation. Iron supplementation or Pepto Bismol can also cause dark or black stools, as can spinach, licorice or blueberries. Those stools lack the tarry consistency of melena, though, and can be investigated at a more leisurely pace.
Bleeding in the lower GI tract isn't processed as it is in the upper tract, so the blood will remain a reddish color. Bright red blood is usually a sign of bleeding near the rectum. Blood may be swirled around in the stool (indicating bleeding farther up), or separate (indicating bleeding closer to the rectum). All episodes of bloody stools should be checked out by a health care professional, and sooner rather than later.
Now, there is a difference between blood-mixed-in-with-the-stool and "red stools." Some poops are just red in color, with no evidence of bleeding. These are often caused by red food coloring or eating a lot of beets. You can usually tell the difference, but if you're worried, take a stool sample to your doctor (they'll love you for this, take my word for it) and they can test it for blood.
Gray or Yellow
Remember that I said stercobilinogen is the brown pigment in stool? Well, it starts out as a chemical called bilirubin, a major component in bile from the gallbladder. If something happens that obstructs the flow of bile (like gallstones), you'll get pale, "clay colored" stools. These are also worth getting checked out if they keep up. Antacids with aluminum in them can lighten the stools too, and if you've had a barium test recently (sucks to be you), you can even have white poo while the barium is working its way out.
Which brings us to your question . . . what causes green stools? Although eating a lot of vegetables can cause a greenish tint to the stools, you mentioned a "beautiful emerald green" color. In my experience this can only happen when you ingest blue food coloring. Think about it: bile is yellow as it comes out of the bile duct. Mix it with unnatural blue dye and you get a lovely green that will result in the kind of turd you described. I'd bet $20 that you ate a blue cookie, or cake with blue frosting, or some weird-colored kids' yogurt the day before.
So that's it, my treatise on fecal polychromatics, which apparently I had a lecture on in medical school. It's amazing the kind of crap we had to learn ("crap," get it? Yecch).
**Remember, don't do anything you read here without first consulting with your own health care provider.**
Dr. Steve is the resident medical expert for the Opie and Anthony and Ron and Fez shows, and the host of his own Sirius XM Radio program, Weird Medicine.