Make sure that you carefully evaluate the source of the criticism before you believe it.
Virtually all the criticisms of the Blood Type Diet which can be read on the internet are the result of partisan politics, usually in the form of an opposing nutritional system or belief.
Not one of these criticisms is founded on any type of scientific evaluation of Dr. D'Adamo's work or a review of the existing science literature on the human blood groups. In fact, most critics would appear to know very little about the subject matter they are criticizing.
Keys to evaluating material critical to the Blood Type Theory:
1. Is it science-based, or just the postulations of a spokesman for an opposing system threatened by its conclusions?
2. Does the critic display a convincing knowledge of the human ABO groups? We've found that many critics of Dr. D'Adamo's work have never actually read any of his books, nor have they taken the time to investigate the theory with an open mind.
3. Does the criticism appear fair and balanced? Is the critic curious about what they are investigating? It is OK to be skeptical, but a surprising amount of skeptics have absolutely no curiosity about that which they are skeptical of.