Came across this response to a question about risk of blood donations causing anaphylaxis.
"Unfortunately there is good reason to believe there is indeed a hazard. We know that proteins are absorbed into the blood sufficiently intact to cause reactions far from the gut. A very well-known researcher called Salvaggio, in the USA, showed that eating proteins could cause a skin reaction on the back where serum from a sensitive person had been injected. We know that cows' milk proteins emerge in human breast milk. So proteins we eat get into the body in a form which can still cause allergic reactions. Unfortunately it sounds as if it is time that blood donors should be counselled not to eat nuts on the day of the donation. I'll take this up with others. Thank you. "