Is there such thing as a generic "metabolic type"?
That book was likely crap, but in short the answer is yes, probably there is a genetic basis in the metabolism, with human 'types' that could benefit from a personalized nutrition. The discipline studying these relationship is called nutrigenomics, and the main concept is similar to what is being told for personalized medicine. The bad news is that unfortunately this is not easy to identify, surely not from the form of your finger.