参考答案 One Possible Version:

I am Liu Qiang. I think it's not strange to have worries. Some students say they have become fat and that it really makes them feel bad about themselves．I think this is one of the biggest worries for us．But I think we can do something about it．
First, you could eat less. The body needs food for energy, but you’ll become fat if you eat more than your body needs. If you eat less, the body can burn more calories than you eat. Second, do more exercise. Doing exercise can also help the body burn the calories and make you thinner. There are many ways to do exercise. For example, you could go to school on foot or by bike.
Don't worry too much．I think you will become fit soon.