I haven’t heard about the blood transplants, but I have read about the fecal transplants. I have read that accomplishing a fecal transplant from a thin person into an obese person, the obese person loses weight, and becomes less obese. The procedure is also used successfully as a treatment for C-Dif infections.
These are transfusions, not transplants. Blood cells only live a few months as it circulated thru the body.