Exercise increases muscle which helps speed up your metabolism
1 ) Exercise as part of a weight loss plan is much more effective then just calorie restricting through dieting. It can also help maintain and increase lean body mass. By increasing lean muscle mass you will increase your metabolism which is important for weight loss.
Fat burning increases post exercise
2) More oxygen is needed after high intensity exercise for the body to repair damaged cells, refuel energy stores, balance hormones and to neutralise the lactic acid. As a result the metabolism and fat burning increase post exercise too.
Exercising burns calories
3) Exercise burns calories, so by exercising you create a calorie deficit. To reduce body fat you need to be in a calorie deficit which exercising can help to do as it burns calories. Most of the fat molecules are exhaled as carbon dioxide. The rest leave the body through water, such as sweat and urine and other liquids.
When you exercise your body burns fat
4) Initially the body burns carbs and protein during exercise to use it as energy sources, but the longer you exercise the body switches to burning fat to use it for energy.
Fat comes from free fatty acids, during exercise fatty acids are freed to be burned for energy, burning the fatty acids reduces the fat on the body. Exercise enhances fat mobilisation from the body's Adipose depots and fat catabolism by active muscles, which occurs during exercise. Adipose is the most important store of energy.
Glucose enters the muscles instead of storing it as fat
5) After a high intensity workout, insulin sensitivity is increased which makes the glucose enter the muscles instead of storing it as fat, which helps you build muscle which then helps fat burning process.