TOD:
A friend from San Diego used to say that there are three ways to lose weight--diet, exercise, and disease. I prefer the first two, though I've experienced all three.
I've only gained significantly twice in my life--20 lbs each time--and got it off both times. For me, diet is the fastest and most effective, but I do try to exercise, too. I can lose without dieting, just on my stationary bike, but it does take a while. I notice that each time I gain and lose the weight shifts a bit, ie I'm not exactly the same size as before, even if I'm the same weight. Most difficult on the wardrobe! Another incentive to reach my ideal weight and just stay there!