<<Disclaimer: Verify this information before applying it to your situation.>>

Down here in NZ we don't have an emormous variety of soya sauces to choose
from, but the only one I can tolerate is Tamari wheat free (which is also
GF). Be careful as they have a low-sodium one which is not GF.

Someone else mentioned a meal which contained caramel colouring - I
understand that this might be the source of the problem. Often so-called
"natural" additives are not GF, but the only way to find out is to call the
supplier,no doubt.

Sue
David & Susan