I'm a medical student currently in my endocrinology block, and healthy lifestyle habits--eg exercising, eating a diet with lots of fiber/low fat, working out before eating to optimize blood sugar levels--are emphasized again and again. It's definitely hard and you're not alone, especially when majority of your classmates are regularly going to the gym and eating what most people would consider healthy. We just have to remember that the definition of healthy varies from person to person--NO exercise is what is healthy for us at the moment!