This week we produced our first Water Short, a short podcast five minutes or less with one big idea. This week we ask a question: When you lose weight, through which orifice does it leave? It’s something we don’t typically think about, but you may find it interesting.
So one day we got to talking about weight loss. When a person loses weight, that mass has to leave their body. It’s not like the mass just vanishes.
David Ladner
Transcript
David Ladner:
Hello, everyone. Robert, Amy, and I are working on producing the second episode of The Outfall Podcast. It’s an interview with Layne Carter. Layne is an engineer at NASA and he’s the water systems or the water subsystem manager for the International Space Station. He has some pretty interesting things to tell us, so be on the lookout for that podcast in the coming weeks. In the meantime, we’re playing with water shorts, little tidbits of podcasts each with a fun little piece of information to share.
David Ladner:
Our first water short starts in a classroom at Clemson University. I, this is David speaking, teach a graduate course on principles of environmental engineering. We talk about mass balances, diffusion, convection, fluid mechanics, those sorts of things. So one day we got to talking about weight loss. When a person loses weight, that mass has to leave their body. It’s not like the mass just vanishes. The little molecules of whatever, they have to travel out of the body somehow. It’s something we don’t typically think about. And so the students and I were considering this and we thought we needed some help from maybe a biologist. Immediately after my class is Dr. Kevin Finneran’s class called biological principles of environmental engineering.
David Ladner:
So I wrote on the board, “Dr. Finneran, when you lose weight, through which orifice of your body does it leave?” And I covered it with the pull down projector screen. Finneran doesn’t use as much PowerPoint, so when he came into the class, he raised the screen and there was his question. And I wish I’d been there to see his reaction for myself, but the students tell me that he was a bit annoyed and said something like, “Tell Dr. Ladner if he does this too much, I’m going to kick something up his orifice,” but he settled down and they discussed the topic. It turns out that a lot of what happens when you lose weight is the same reaction that happens when burning something with fire. Oxygen meets fuel, the body fat is the fuel, and carbon dioxide is produced.
David Ladner:
So if we’re following the carbon part of the fat, which is a lot of its mass, then the form of that carbon that leaves the body is carbon dioxide. So then where does the carbon dioxide go? My first thought, since I’m a water guy, was that it leaves in the urine. Most of the reactions in our body happen in water with everything being soluble, so I figured that carbon dioxide would be dissolved. It would probably convert to bicarbonate and then you’d excrete it in your urine. But Dr. Finneran explained that the body has a very good carbon dioxide regulatory system. If we get too much CO2 in our blood, it’s a bad thing and it needs to removed very quickly. The body can’t wait to urinate it out, so the faster way is by breathing.
David Ladner:
We typically think of breathing as a process to bring oxygen into the body, but it’s likewise a process that removes carbon dioxide from the body, inhale oxygen, exhale CO2. And the exhaling CO2 part in some ways is even more important. In fact, when you hold your breath under water and you come up for air, the first thing your body wants to do is get rid of that CO2 that’s built up. So you want to exhale before you inhale to bring in new oxygen. In short, when you lose weight, through which orifice does it leave? Through your mouth and nose and the air that you exhale. You literally breathe out your body weight. Crazy, right? And it’s cool to think about because that mouth is the orifice through which you ate all those Chick-fil-A sandwiches to make yourself fat in the first place.
David Ladner:
And when you go to the why or wherever to burn it all off, it leaves through that same mouth orifice. Now then for you strict engineers out there, yes, there’s probably some body mass that leaves through your sweat and your urine too, through your skin pores and through your urethra. And we didn’t talk about the hydrogen and other kinds of atoms in your body, but we’ll save those orifice discussions for another day. Thanks for listening to this quick little tidbit. We’ll be back soon with more. Today, just remember that when it comes to body mass, your mouth is the intake and it’s also the outfall.
