oh noes i have a slow/fast metabolism
its worth remembering that any classification of your metabolism as undesirably fast or slow is describing it relative to your ability/desire to eat food
I doubt many people have accurately determined their bmr and found how it compares to the average person's bmr. What theyre saying is, for a "fast metabolism", their bmr exceeds the amount of calories that they like to eat in a day. That could be like 1500 cals or less, easily. A lot of people dont like to eat much
Someone who complains of a "slow metabolism" may possibly have a bmr of like 2500 cals, but is only satisfied with an intake of 3500.
Since most people never know how many calories theyre eating, people just say they have fast/slow metabolisms.
For example, I know that at a certain fairly "basal" level of activity, I will lose weight at about 2500 cals. However, if I was just eating for pleasure/satisfaction like most people do, id eat well over 4000 a day without thinking about it. It would be wrong to say that I have a slow metabolism, but if I wasnt aware of and (fairly) in control of my diet, I might diagnose such a state.