I was once 135kg's worth of a guy. xD.. (297lbs) .. right now, its 82KG (180~ lbs)
... hmh, how did i loose weight?..
1 .) The easiest solution; ive started smoking with 17. you wouldnt believe how fast you loose weight by just doing that.. since the body tries to cleanse your body from the shit you smoke, and even if the body's efforts arent worth a lot, there are still calories burned in the process.
2.) when i lost around 20Kg by just smoking, i was a bit more self confident, which led me to sign up at a Gym, while reducing the smoke. when i am really up for something, i run 15km's+, but its mostly around 5, twice a week. in addition, i do 30 minutes of excercises, 15 minutes before, and 15 minutes after i ran.
edit: since i've started to visit the gym, i can eat like the big ones, i think i eat around 2500 calories a day, without gaining weight at all.