I think there is some truth to the Blood Type Diet. I have type AB, and I also have very low stomach acid, and it's hard for me to digest meat. So I limit my meat intake to: seafood once or twice a week, and grass feed beef once or twice a month. The rest of the time I eat lots of greens, nuts, seeds, fruits & veggies.
But there are many things about the Blood Type Diet that I don't agree with. Like type AB is supposed to tolerate dairy products really well, and I react horribly to dairy.
But there is other good advice for my blood type like smaller more frequent meals and paying attention to the "food combining" guidelins.
I personally like to pick and choose useful bits of info from so many different "diets" like the SCDiet, the NSDiet, the Paleo Diet, the RAW Food Diet, etc. Overall the current diet that I do eat which is a combination from the ones listed above (and absolutely LOVE) works so well for my body, that I am now pretty much pain free most of the time, just tiny little aches here and there on occasion from damage already done. But I no longer feel the diesase progressing, and I thrilled about that.
Rawking Raw Food Living! http://bettyrawker.com/
Enjoying a plant based mostly raw vegan diet 90% of the time, with a few raw or cooked seafoods every now and then. Taking curcumin daily and combined with a super Low Starch Diet am pretty much pain free!