Resolution to the Poop Volume Question

So I thought about it and also talked to Daniel who pretty much knows everything that’s important to know, about the whole ‘Where does my food go exactly’ question I asked in my last post.   Independently I had decided that mass to energy conversions don’t happen in your body, and that’s not why the volume of food-stuff decreases as it moves through you, but that food mass, like glucose or other sugars, is converted into other substances that you release, via cellular respiration, without you really realizing that you’re releasing them.  Look at this equation:

 

We take in sugar and oxygen and produce water and carbon dioxide.  Carbon dioxide we breathe out and water we can sweat or pee or also breathe out.  So la-tee-da, there you have it.  Obviously this doesn't give the whole story, because we don't just eat glucose, we eat complex carbs and protein and fat, but I think it's the same sort of idea.  Except when you burn proteins and fats you produce some other metabolites like urea and ketones.  However just to be sure, I asked Daniel if mass to energy conversions do actually happen in your body and he said “YES!”  Apparently whenever you’re breaking down something chemically and releasing energy, the sum of the masses of the broken down parts will be less than the mass of the whole of the thing you started with.  I’m pretty sure I learned that in some class at some point but in application, I guess it didn’t stick.

 

By the way, it seems like biology teachers, or at least all the ones that I know about, introduce the whole cellular respiration thing as, “this is how your body gets energy!”   I think it’s a lot more interesting to introduce it this way, e.g. “Have ya’ll ever noticed that the volume of stuff that you eat is much larger than the volume of stuff you poop out?  Why is that?”  That seems like a much more likely thing to wonder about than, where your body’s energy comes from. 

Science is the best tool I know of for making sense of things, especially biology since that’s what most of my questions are related to, and I think it’s important to convey that idea to students – that you can get a lot of your questions ANSWERED!!! if you just learn a little science!