new here, looking for info

Hi:
I've just recently heard about the Blood Type Diet s and I have some questions that somebody may be able to answer. First, how did they discover the particular items that each blood type needs or doesn't need?

And I read in a list of foods for type A, that there is secretory and nonsecretory, what does that mean?

Since the blood type A almost has no meat available, does it make it a vegan diet?

I have some health problems and I want to make sure I'm feeding my body correctly. But I'm unsure that I could go all the way vegan. Thanks, LJ