QUESTION: I was listening to a health guru-type guest on a radio talk show recently and when a listener called in and asked her opinion on the blood-type diet she scoffed. She claimed that horses, for instance, have at least 12 blood types but they all consume the same foods. I know people aren't horses but humans are animals, ultimately. I don't have the research background to respond to her criticism. Can you help?

ANSWER: Your critic doesn't have the actual number of blood groups in the horse correct and I would expect under these circumstances that the basis of blood group effects in human (gene linkage) might be as lost to her as well.

There are eight recognized blood groups in the horse: A, C, D, K, P, Q, T, and U. (These are similar to A, B, AB, and O groups found in humans). However, unlike our blood types, each of the horses' blood groups can exist in one of several forms. For example, to say that a horse has type A blood is not enough because type A may mean type aA1, type aA', type aH, type aA'H, or type a. And, in addition to having a blood type from the A family, a horse may also have a type from each of the other seven groups.

Almost all species (including even primitive life forms such as bacteria and parasites) have some blood group expression; however they vary greatly in the degree of genes linked to ABO that convey any physical variations.

This is where the effects of blood group in humans places them in a special category: ABO genetics influence stomach acid and intestinal enzyme production probably because their levels are linked to the ABO gene locus, but this is probably a specific linkage found only in humans.

Since the gene for blood group is found on entirely different chromosomes in various animal species, one could only expect that differences in physiology linked to blood group would be different as well. A black colored hair coat is found in many pigs who are group O blood; obviously this is not a phenomena shared with humans.