That's one of the reasons it took me a while to realize that "fast/slow metabolisms" really aren't a thing. At least in a practical sense. I'd hear people at school talking about how hard they're working out and see little to no progress with weight loss. Where I was skinny while never setting foot in a gym.  What I was't getting is that their most active workouts didn't even hit the caloric burn of what I'd describe as a lazy day spent doing nothing. My innocent mind hadn't even seen the realities of people driving to their mailbox or to something a block or so over.