I really can only speak in anecdotes, but almost to a person, people I know who have combined improving their diet with exercise have been far, far more success

I really can only speak in anecdotes, but almost to a person, people I know who have combined improving their diet with exercise have been far, far more successful in both the short and long term in losing weight and improving the way they look. Everyone who has focused on diet alone tended to look miserable and weren't successful in the long term, even if they managed to lose a good amount of weight initially.