Do you know that after the over consumption of food , the excess glucose is converted into glycogen which is stored in liver and muscle by the duration of time, if it is not used then it is converted in lipid or proteins which are commonly known as fats.
The amount of fat in the body could be reduced by diet and exercise both but according to my point of view, exercise is better than various strict diets because as you do exercise, your calories burns and the fats, stored in the body starts breaking and converting into glucose
During the above process that fats releases free radicals which may be harmful. But while you are exercising, these free radicals are removed from the body as a part of sweat. But if you go under strict diets than fee radicals may harm the cells of your body.