At risk of re-creating the vegetarian thread....I am a fitness instructor (Spinning) and body builder. I followed a total vegan lifestyle for almost 15 yrs. Yes - I am a type O. I got weaker, and weaker, sicker and sicker and ironically....I couldn't take off that last 5% body fat.
I went though series of allergy tests...to find that I was allergic to almost everything that I was eating. To put it mildly, I was sick, depressed and scared.
I read ER4YT and was AMAZED at the lists of contraindicated foods for type O. It looked like a perfect match to all of my allergy tests!
I am doing a lot better now, digestion is better, energy is better, bodyfat is low.
Morally and ethically I may believe in the vegan diet....but it almost killed me. Eating isn't as much "fun" as it used to be, but I am feeling great.