Also, you don’t absorb everything you eat. Actually, let me be clear: I have no evidence for this. But the fact that my weight is so consistent despite my radically inconsistent eating and exercising suggests to me that my body can regulate digestion. When I’m in a period when I’m overeating, my body just doesn’t absorb so much.

Again, more speculation, but i would imagine that metabolic disorders involve digestive regulation issues, not just lack of exercise and overeating.