Exercise is good for you, I guess. It’s probably one of the better options for anyone who’s trying to lose weight. But when you exercise, where does the weight go, physically speaking?
The first time someone asked me this question, my best guess was that it had something to do with Einstein’s E = mc2 equation, the equation that allows matter to be converted into energy. But I knew that couldn’t be right. That’s more of a nuclear physics thing, and the human body is not a nuclear reactor.
The actual answer has to do with chemistry. Rather simple chemistry. This is a triglyceride molecule:
Okay, it is sort of a complicated-looking molecule. Don’t worry. Your body knows what to do with it, even if your brain doesn’t.
The important thing, in relation to today’s question, is that triglyceride is composed almost entirely out of carbon and hydrogen atoms, with a few oxygen atoms sprinkled in.
Now when your body exposes triglyceride to the oxygen you breathe in, that highly reactive oxygen starts breaking the triglyceride molecule apart. With each chemical bond that breaks, a little bit of energy is released (allowing you to keep exercising), and the broken pieces of triglyceride recombine with oxygen to make carbon dioxide (CO2) and water (H20).
It’s worth noting that chemical bonds do contribute marginally to the total mass of a molecule, so when you break them and turn them into energy, E = mc2 does apply, sort of. But that’s nowhere close to being a significant factor in terms of weight loss.
The vast majority of the weight you lose comes in the form of carbon dioxide, which you breathe out through your lungs, and water, which you sweat out or pee out or breathe out as water vapor. (If you want to get into the math and find out how many kilograms of oxygen you need to burn how many kilograms of triglyceride, producing how many kilograms of water and CO2, click here.)
When I started studying chemistry, this was not the kind of thing I was hoping to learn. I’m a science fiction writer. I’m interested in the type of chemistry that makes rocket engines go, or drives weather patterns on other worlds, or could make alien life possible.
But still, it’s exciting to me when I can connect all that outer space science to some of the mundane aspects of life here on Earth.
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Today’s post is part of a special series here on Planet Pailly called Molecular Mondays.
On the first Monday of the month, we take a closer look at the atoms and molecules that make up our physical universe, both in reality and in science fiction.