Maybe it shouldn't be surprising, but without the knowledge, the opposite of the thing can be explained the same as the thing itself. For example, "The energy you take in has to go somewhere", but I also poop everyday, so maybe I just poop out the unnecessary calories? I know it works for water soluble vitamins for example.

Hindsight is 20/20 in this case. It's nice that the explanation is not complicated ("calories in, calories out"), but many other simple things have been thought of as true, only to be put on their head by science. I welcome the scientific confirmation, and I hold that the path to knowledge it's not straightforward at all.