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Metabolic Chamber

We get fuel in the form of calories — from carbohydrates, fat, and protein. But to unlock those calories, the body needs oxygen. When we breathe in, oxygen interacts with the food we’ve consumed, breaking down (or oxidizing) chemical bonds where the calories are stored and releasing them for use by our cells. The product of the process is CO2.

https://www.vox.com/2018/9/4/17486110/metabolism-diet-fast-weight-loss