What is the purpose of the metabolic typing diet?

What is the purpose of this diet? Is it to lose weight or just for gerneral health?

I don't need to lose weight but I have a very, very fast metabolism and a huge appetite to go with it. Actually I eat so much that it's often awkward. Is there a way to control this?

I did the "niacin" metabolic test that cbrown gave in his post. From that I seem to have a meat-eater type metabolism. After taking the niacin the first thing which happened to me was that I got a really sharp pain in my stomach. Then my skin got hot and itchy and a little puffy. It looked like I had a rash all over my body. When it went away I had a pastey taste in my mouth.

Does any of this have anything to do with having an abnormally fast metabolism? What can I do to slow my metabolism down?