Just to clarify, metabolic typing is not the same as blood typing, and the results of the metabolic typing lab work don't necessarily result in the same dietary recommendations as the blood typing paradigm.

The reason that there isn't a wealth of clinical studies about metabolic typing is that the paradigm is where low-carbing was about 30 years ago in terms of acceptance. The medical profession villifies it or ignores it, and the public hasn't heard of it. But, metabolic typing does have a 30-year history of its own, and recent refinements about 10 years ago have made the methodology comprehensive. The research to date has been methodical, but limited and private (not peer-reviewed). Metabolic typing practitioners haven't marketed any special foods, other than specially formulated supplements for each metabolic group. So, nobody has a big advertising budget to promote their books or their agenda.