If you search this forum you should find a thread discussing our blood types. O was by far the most common, a bit more than in the general population where it also predominates.

From there you need to google "Blood type diet" which will bring up a book or three written by an MD whose name escapes me. NYT best seller if I remember right and very level headed. The idea is that over the millenia, the human race began in Africa and migrated in various directions. One group went in one direction, domesticated cattle and adapted to drink milk. Another went another direction, developed agriculture and adapted to grains. The mix of your genes from this pool determines your relationship to the foods available. Type O has a lot of the original genome and not so much of the new, so we thrive on meat, leaves, and roots - aka the Paleolithic Diet.