To keep yourself in fit you should do just a few things: 1. Eat healthy food 2. Do fitness You shoud not eat too much, few times a day, but not before sleep. If you want eat something very much it's better to drink kefir (вроде так и есть) or eat an apple. But the best of you can do is to do something useful and don't walk near frige. Moreover you would not be upset about eatten cookie. Also you should not tire yourself too much while doing exercises. If you can't visit gym do sports at the morning. This is the most elementary advices to keep you in fit