Scientists call poop feces, the Latin word for the dregs that settle out of wine. I think they might be trying to be classy.

Feces are made of:

  • Substances from food the body didn’t want.
  • Substances the body wants to get rid of.
  • Food that didn’t break down.

Strange though it seems, the gut is outside the body, since it forms a continuous tube from end to end. The body tends to chuck waste into the gut to get it out of the body.

This means the last component; food that doesn’t break down; is important in our diets, where it is known as roughage or fibre. The body doesn’t want feces full of the body’s toxic waste in contact with the gut wall: roughage gives something for the gut to push on to help clear feces out of the gut.

The colour of feces is mostly due to substances the body needs to get rid of. Blood contains a red chemical called haemoglobin, which helps red blood cells move oxygen from the lungs to the where it is needed. Red blood cells can be damaged by being constantly shunted around the body, so after about 100 days in service they are scrapped in the liver.

Scrapping the red blood cells means dealing with the old haemoglobin, which is broken down into a substance called bilirubin, which has a yellow green colour. Most bilirubin is made in the liver, and is dumped into the gut via a pipe known as the bile duct. Liver failure can cause your eyes and skin to turn yellow. This is called jaundice and is caused by the buildup of bilirubin in body tissues, as it can’t be processed by the liver and passed into the gut for excretion.

Bacteria in the human gut then convert the bilirubin into a brown substance called stercobilin which gives feces their colour.

Changes in colour of feces can show you’re not well. For instance feces can appear green if feces are moved through your gut too quickly. This is because bilirubin is yellow-green before bacteria convert it to stercobilin, so if bacteria doesn’t have time to convert before you go to the toilet, it will still be yellow-green.

More seriously, if you’re feces look like the water drained off cooked rice, you should wash your hands and go to hospital. This is because you have got one of the most dangerous diseases humans have faced: Cholera.

Cholera is a form of diarrhoea so severe it can stop the body getting the water it needs to survive, leading its victims turning blue and dying. Fortunately, Cholera is not currently prevalent in the developed world, largely due to improvements in water supply and sewers.

Science can reveal surprising truths about ourselves, even from things we find as disgusting as our feces.