Well most of the slow vrs fast metabolism is just pure myth.
It has more to do with body types, then diet and activity levels.
You have ectomorphs, endomorphs etc and that plays a much bigger role.
I could write about 6 thousand lines on the topic.
DNP is one of the only compounds, or triidothronine that will actually alter metabolism in a human(and DNP is a derivitive of TNT, yes the explosive, its very very dangerous)
Then there is also thyroid function, hormone levels, neurotransmittors, leptin, grehlin etc all involved.
Its a very complicated situation but its very easy to lose bodyfat if you have someone on your side that understands all these factors