1. Find out how much calories you need eat per day to maintain your weight (use an online calculator) and eat less than that.
2. To make it faster you can lift weights (I use this routine ICF 5X5) but you have to make sure your eating at least .8 grams of protein per pound of body weight and subtract 200 calories off the calories you need to maintain your weight.
Example: If you need to eat 3000 calories to maintain your weight you eat 2800 calories
If this is too much to start with now just east eat less food than you already do and get more active. (no prone masturbation does not count)