I might be wrong and I'll be gladly proven wrong with a study, but every time someone says I have a fast metabolism just because I just ate a huge ass pizza right before their eyes, hurts my soul. Everyone that has tolled me this so far has a drastically different lifestyle from me. I don't eat that much most of the time, I often just get a salad or tuna sandwich. I also move my body a lot more, unless I absolutely have to use transit, I WALK. These people always cringe when I tell them I parked the car more than 5 mins of walking away and fucking refuse to walk to it with me.
Yeah I think there is a lot of misunderstanding by these individuals. Faster and slower metabolisms certainly exist (especially varying across values like age, sex, and hormone levels), but outside of medical science circles the “fast metabolism” label is often misapplied to situations like yours, which are much more concretely explained as a difference in lifestyle. :) Thanks for sharing.