Exercise is critical for maintaining lean body mass in weight loss surgery patients. Also, the greater the caloric restriction and rate of weight loss, the greater the loss of lean body mass.
This is consistent with the popular advice of limiting weight loss to 1-2 pounds per week. Obviously extremely obese people can safely lose weight faster than that at first… but how much faster? And should weight loss be limited if exercise is emphasized (e.g. The Biggest Loser)?