Our son has eaten the same chicken breast at a restuarat that we trust for about 4 years now. He has severe allergies still to wheat, milk, egg, and peanut - he used to also have corn and soy. Well, my husband and I always ordered him a "plain" chicken breast almost every time we visited. About two weeks ago, the manager told me that he noticed that the chicken breast was not on their "gluten free" list. Interesting! Well, apparently the chicken breasts are pre-marinted with a LONG list of ingredients including a "contains: wheat and soy" disclaimer. We were shocked! He usually broke out in some red spots on his face after he ate there but we just assumed it was nothing - he has very sensitive skin and breaks out in splotches for no reason sometimes! Although, I did have to give him benadryl after one visit.
The lesson learned: always ask about whether or not meat is marinated - never assume that it is just meat. Marinades may contain ANY of the top allergens including wheat, soy, peanut, sesame, etc. Always be safe and ask!