Fat is not expelled from the body as “fat”.
You actually breath and sweat your fat out.
When your body needs more energy than what is available from carbohydrates and protein, fat is converted into energy.
This process produces oxygen and water when it breaks down the fat.
The oxygen is breathed out through your lungs as Carbon Dioxide, and the water is sweated out.
By not eating (intermittent fasting, such as not eating until midday), HGH (Human growth hormone) is released in your body, which breaks fat down.
You also need to move your body to start to break the fat down.
Intermittent fasting, low calorie diets, lots of sweating and huffing & puffing will break down the most fat.