One question here is, how long is 'before long?' I could pull out a Kevin Hall study showing loss of lean mass in a metabolic ward setting on low carb relative to high carb, but then you could pull out longer term studies where after a period of adaptation, it's more of a wash. Weight lifting studies showed greater lean mass after a low fat weight loss diet versus low carb until they started doing a carb up at the end of the study--then it flipped, higher lean mass gains for low carbers. But the difference between carbing up and not is going to be mostly glycogen. Until somebody comes up with a strong reason to change my opinion, I'm going to figure it's a wash, just make sure I get in enough protein and work out on a regular basis. Still eating low carb, but not over lean mass, more because it seems to give me a better mood/energy and is easier to stick to/controls my appetite. Although--I do think the mood/energy things makes it easier to stick to the workout routine.