I want to first start by saying that the fats you consume in your diet are not the same as the fat that you have stored on your body. As noted in our previous newstrition regarding fat vs. carbohydrate fuel, fat is burned more slowly than glucose - making it the perfect energy source for long, low intensity activity.
Once digested, fats (avocado, egg yolk, salmon, nuts) are stored in the body as triglycerides. Our body has the ability to store boat loads of fat. The body can indeed store excess dietary fat as body fat, but body fat can also come from other sources, such as excess carbohydrate consumption.
When someone "burns fat," the fat molecules are broken down into their component parts, which are carbon, hydrogen, and oxygen. These components are then released into the bloodstream and transported to the body's tissues to be used as energy.
In a peer reviewed study published in the BMJ, scientist decided to follow the path of the carbon hydrogen and oxygen atoms that are all part of fatty acids (aka the fat that is stored throughout the body - not the dietary fat you eat food).
According to these scientists "10 kg of fat is oxidized 8.4 kg of that fat is excreted as carbon dioxide, and 1.6 of those kilograms is released as water". In other words...https://colinelovecat.blogspot.com/2017/10/adipose-tissue-human-body-fat.html
approximately 84% of the fat you lose is actually eliminated through your breath when you breathe out!
So, to sum it up, when someone burns fat, the majority of it is exhaled as carbon dioxide in your breath, and the remainder is excreted as water through various bodily fluids.