My wife has recently lost quite a bit of weight; she's at probably her lowest adult weight in her life now in her 40's. Many people who see her ask what her routine is and how much she exercises.

As it turns out, the simple rule of "calories in, calories out" is true and possibly the easiest heuristic to follow to lose weight. She has hardly increased her metabolic activity (calories out), but primarily shifted her diet (calories in).

The mentality around weight management would do well to focus more on sustainable diet changes rather than on exercise (not that the latter isn't important, but that diet management seems to me more attainable and effective).