Dave Asprey managed to have lose weight at >4000 calories per day. A QS friend I know replicated this and found that adding 1000 calories per day in butter for a month didn't raise his weight either. My own attemts to raise my weight by throwing ~800kcal of maltrodextrin per day into my tea also didn't raise my weight.

Metabolism is not only important between individuals but also changes day to day due to different hormones.