Comment by fian

To lose fat, the biochemistry requires conversion of long chain hydrocarbons (fats) to carbon dioxide and water. For a good explanation see:

https://www.abc.net.au/catalyst/where-does-fat-go/11015048

To burn fat, you need to eat less food so you tap into your fat stores, but you also need to breathe in oxygen and breathe out the carbon dioxide and water.

Exercise essentially helps to decrease your glycogen stores so you get to a fat burning state and in breathing more which will help get more oxygen for the reaction and expel the carbon dioxide and water that are produced.