You mentioned that most Native Americans are Type O. I was wondering (being a type O as well) about the use of corn, since many tribes have used that as a staple.
Corn is a sacred food in many native American cultures. Unfortunately, that doesn't make it any better of a health choice!
A good example of the effect in adding corn into the diet of these type O native Americans can be observed in the bone remains of the Indiana Mound Building cultures, since we can exactly trace the introduction of corn into the diet following a long prior existence as hunter-gatherers, by the marked change in the bone structures. Prior to corn becoming a staple, the bone show little arthritis or thinning, after corn is introduced, bone deformation begins, including major changes to the teeth structure and jaw (periodontal disease). (1) In addition, maize stimulates a very rapid and powerful glycemic response,(2) so it may be that the switch to a maize-based diet from prior hunter-gathering may have been responsible for the precipitous increase in diabetes.
If corn lectins are problematic for type O, they are even more of a serious hemagglutinin in those people who are type B or type AB. Interestingly, those red blood cells of those who were blood type A2B where clumped more aggressively than those who were A1B.(3) Also of interest was the observation that corn lectin continued to persist in even the purified oil. (4)
1. Gagne G. [Mouth diseases in a prehistoric agricultural population of northeastern North America]. J Can Dent Assoc 1993 Aug;59(8):686-92
2. Segal I, Joffe BI, Walker AR, Stavrou E, de Beer M, Naik I, Daya B. Glycaemic responses to different carbohydrate foods in healthy and diabetic blacks in Soweto.S Afr Med J 1991 Dec 7;80(11-12):546-9 Related Articles, Books, LinkOut
3. Prodanov P, Atanasova N. An anti-B lectin from Zea mays everta. Folia Haematol Int Mag Klin Morphol Blutforsch 1984;111(1):84-5
4. Klurfeld DM, Kritchevsky D. Isolation and quantitation of lectins from vegetable oils. Lipids 1987 Sep;22(9):667-8