It's necessary to keep your fit. There are many way for you keep your fit. But I think you can notice some point. First, you should do exercises regular such as swimming, jogging, or ride bicycle. The second, you should have a good diet, eat enough the nutriment and usually have breakfast. You should eat less meat, more and more vegetable, fruit, salad, and drink a lot of water, about 1,5l to 2l per day. Next, you should go to bed early, not stay at late, and at least 6 hours per day. And finally, you shouldn't work too hard, reduce the pressure and stress. That is many way to keep your fit, you can do it.