text: Most doctors, if not all, say exercise is good; however, by changing your eating habits, your weight (stomach) will go down and you could probably get away with doing alot less crunches (yuck!)  I ate more protein (chicken, fish), green veggies, lots of water, limited carbohydrates (go online or get a book) and continued running (not as much as you), and have kept my weight off and have done so since I had my twins 28 years ago.  Congrats on your commitment to running...it's cool to get that second wind and makes you feel like you could run forever and ever.  However, over the years (unfortunately it has been several), I have found that once you stop exercising, fat sure starts coming on quicker than if you hadn't exercised at all.  I picked Yoga and Pilates (bad back) and it has been quite successful.  You are 17 right now, get your body back by changing your eating habits and continuing to exercise (just don't get carried away if you know what I mean) and your weight and stomach will both start showing improvement more quickly than you could imagine.  The good news is that your skin is still able to bounce back and hopefully you will avoid those awful stretchmarks.  Like I said previously, I had twins at 22, went over 200 lbs when I delivered, and can honestly say I do not have any stretchmarks, do not eat diet or no fat foods (again, yuck!) and my body looks pretty good for being in my 50's.  Another word of caution....understand the meaning of MODERATION.  It's all part of the life cycle.  Good Luck.