Part of that 'black box' to me is what carbs did to my appetite and my metabolism. A calorie is a calorie absolutely pointless to me. Not in theory, per se. Amount of calories still a very real import to me and anyone else. But in reality it was such bad, pointless advice to focus on.
Carbs kept me hungry. Pointless to restrict calories because on high carbs I was incapable of doing it. And my body held on to fat and accumulated it on high carbs.