Do you ever catch yourself wondering about all sorts of things when you're working out? How about the one time in 5th-grade gym class where you got pants'ed, last night's episode of This Is Us, how good that post-workout smoothie will taste, or even, "where does all this fat go that I'm surely burning at an incredible rate?"
Our bodies are complex machines that science is just beginning to truly understand. From our varied emotions and psyche, to our symbiotic relationship with our gut-biome, other than outer space, the body is the final frontier. So what really happens to our fat as we start to move-it move-it?
It disappears into thin air! No, seriously.
The conservation of mass states that energy is never created or destroyed, it merely changes form. The same is true for the energy that we eat. So when you're cranking it to 11 on the treadmill and your body says it needs to burn our stored fat for energy, your body sends out different hormones to summon triglycerides to convert into go-go-juice (think of triglycerides as the stored energy that live in your fat cells).
As your heart pounds and your legs quiver from awesomeness, your body can't turn all of that stored energy into direct output, so these triglycerides produce two byproducts from the inefficiency: ~15% H2O and ~85% CO2.
So what happens to the "fat" now?
Now the body gets rid of some of the water in the usual way (think bathroom breaks and that gross sweaty guy at the gym), but according to a 2014 study in the British Medical Journal the rest of that water and carbon dioxide is expelled through all your huffing and puffing! As your magnificent machine churns out the miles, it's taking all that extra CO2 from burning fat and expels it with the CO2 produced while your lungs process oxygen.
I'm not going to say that burning fat is always a glamorous process, but next time you find yourself questioning whether or not your workout is actually working, just remember this silly thought: "Am I breathing? Great! It's working!"