<<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