As I understand it, a recurring issue is that patients do not often change the underlying causes for their obesity, which is poor diet and a lack of physical activity. They lose weight, but it’s as a result of decreased appetite and the nausea they get when they binge, but once they start losing weight they see no reason (or lack any motivation) to do any weight training or cardio.

Not saying that’s the case, obviously, but muscle loss when you go on a deficit is expected.