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I have just read a bit in a Miss Manners book on food allergies, I thought
to pass it on

"No host is going to be at ease while being grilled about all the
ingredients used in dinner. Perhaps he secretely ordered carry-out food and
has no idea what is in it..those with extremely complicated food problems
are advised to eat before social events, so that they may survive if
nothing is available that is beyond suspicion...you could also request from
people you know fairly well that a piece of plain meat, fish or whatever be
put aside for you without any sauce whatsoever."