I think that the food we eat plays a huge role in staying fit. Nevertheless, it's also a good idea to do some kind of exercise and going to a gym is not mandatory. You can walk, run outside, dance either at home or at school, play a team sport. And there are so many available exercises for all kinds of things, especially in English on YouTube for example. But it's always good to be aware of our own physical limits, respect our bodies, believe in ourselves and most of all, be patient because we don't get results overnight. I also think that establishing good habits of eating and exercising go a long way. And lastly, over the years I realize that staying fit depends on the specific person, there are people that have a tendency to fatten and others have difficulties gaining weight, so the plan should always be specific for that person. You can make a plan by searching and experimenting news things, to really see what works in your own body and to see what you enjoy doing and eating.