Mainly exercise. People think there is some magic to weight loss but, in reality, you walk two miles a day to start and built it up to five over a year or so. The media always tries to claim exercise is pointless, showing you barely burn off a coke in an hour of walking but in my experience you walk two miles a day at least and it will become impossible to be obese without trying (e.g. cramming food down your throat till you feel sick every day). It has got to be burning more than the media lets on.