Wednesday, January 18, 2012

A scatalogical myth

"In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return."
Genesis 3:19 KJV

I teach high school biology. I happen to love teaching, and I enjoy learning how things work, but many of my lambs come to high school with some deep misconceptions that skew their world view.

It's mid-January, a busy time of year, but I need to take a few moments to talk to my colleagues at the elementary school level., yeah, you....come a little closer.....poop is not digested food.

The food that gets chopped into bits tiny enough to enter cells either ends up as part of you or exits as part of your breath (CO2) or your water.

When you diet, most of the you you lose is lost as carbon dioxide, bits of you lost with every exhaled breath. Some is lost as water, some as urea, but most of it gets cast off with each breath. I once lost 60 pounds, breath by breath by breath.

Why does this matter?

It gets the knee-high crowd thinking of mass ("stuff") as something other than solids. It complicates the whole food to poop business.

Trees are massive hunks of stuff made mostly of carbon dioxide drawn in through tiny holes in their leaves. We're massive hunks of stuff made from the stuff we eat, stuff mostly put together by plants.

Carbon dioxide to food to carbon dioxide again.

Thou art carbon dioxide, and to carbon dioxide shalt thou return.

OK, bile comes from RBC's, which were once food--but this does little more than give poop its lovely colors.


Mindy said...

Thanks for posts like this. I'm one of those elementary teachers and I value advice helping me send them off with correct understandings.

So help me...poop isn't digested food. What is it?

And can you answer this: Let's say you weigh 100 lbs in the am. You eat a 3lb chicken. Would you now weigh 103lbs if you weighed yourself right after? Then, the next day, you've digested it. However, you've lost some as CO2, right, and perhaps added some fat? So you now weigh 101 or 102?

Or is that simplifying it too much?

doyle said...

Dear Mindy,

Poop is largely the stuff you can't digest ("roughage") as well as lots of bacteria that munch on the stuff we can't use. Poop has a lot of water as well.

The color comes from bile pigments, which come from broken down red blood cells and other tidbits.

You would indeed weigh 103 pounds right after, plus the weight of whatever you drank. (3 pounds is a LOT of chicken!)

You may or may not have added fat--that depends on how much energy (calories) your body needs during those few hours before your next meal. Much of the excess is stored as glycogen in the liver and muscles.

Most of us who aren't lose some weight as we lose the undigested stuff, but we lose most of the digested stuff as carbon dioxide.

Think of it this way--if you fast, but still drink water, you lose weight fairly quickly, and most of this is through your breath.

You're not simplifying this too much. It's pretty neat, no? Most of what you eat, you breathe out!

Thanks for stopping by.