Working out is very important for over all health and to stay looking young This can be hard to swallow, so here's a quick reminder that your muscles need to be "burning fat" to grow, not burning calories or calories of carbohydrates. You may not get your body to "burn fat," but it will eventually start to lose muscle. It will become harder to bulk up as your muscle mass slows. If you have a high BMI, it could take a long time for your size to return to normal. 

Keep in mind that being a "fat kid" may cause you to gain weight. Use it to your advantage to build your mass back up. In most cases, fat is good for muscle growth, just look at the people who are skinny. When I was young, I put on weight easily and it was the result of having a good diet and not following the "obesity-is-a-cause-of-obese-fat" mentality. You can put off your fat loss by staying too skinny, or eating too many calories.