In your teen years your body burns fat faster than any other time in your life. Regular exercise & a healthy diet is all it takes. Call it old fashioned but if it's worked for this long there must be something to it.
Being kidnapped and held for ransom by Somali religious fundamentalists usually does the trick.
eat proper size portion meals and exercise 30 mins a day... same way doctors have recommended for the last 50 yrs
Date a vamp or lycan.
Cheesy as it sounds, but eat all of the food grounds, eat in moderation, eat a bunch of small meals/ snacks a day instead of three big ones, and exercise !!
Exercise, eat less fattening foods, and drink water.
Proper diet and exercise.