Stay away from foods with large amounts of carbs in them after 3 p.m. Exercise at 3 p.m. If you get the munchies after dinner, eat some chicken (not fried or processed). Eat your vegetables. Don't do heavy workouts, as this may not be healthy for a thirteen year old. Pushups, situps, crunches, wall squats, etcetera are the way to go. Also, jump roping and jumping jacks can be god to do before you exercise. Drink a full glass of water fifteen minutes before your exercising. Lay off of sodas, fast food (not just McDonald's), and potato chips. Stay away from processed foods (certain luncheon meats) and white bread. Doing curls with light weights is also healthy. Eat three meals a day, but make sure breakfast is a small meal. If you have trouble with a certain exercise, don't rush yourself. Slow down until you feel comfortable. After you've been doing it at a certain rate for a couple weeks, take it a bit further. Jogging is good. Ride your bike and swim. There's a diet called "the lemon cleansing diet". It is very healthy and more of a health diet than a weight loss diet. Chances are you will get sick during this. However, it cleans the inside of your body. My mom went on this and lost 40 pounds. It will only make you lose as much as you need to. Google it if you want to know more about it. I hope this helps. Also, if you have any doctor friends, ask them about it. ;)