I had one. My metabolism runs about 15% under what it should for my height, weight & age. Predictably, I struggle with losing weight as every calculator suggests that I eat about 15% more calories each day than I actually should.

I do not have diabetes, my a1c is perfect, my resting heart rate is typically in the low 60s, the highest my blood pressure has ever been tested was 127/89 and the lowest has been 87/65 (pre-hypotensive).

I guess what I am trying to say is that human metabolism is not standardized and does not fit into a single conceptual block. I would have to actively exercise for a 30 minutes a day or more to equal out the calories burned by someone with a normal metabolism who sat on their ass all day.