My daughter is allergic to corn, so we often ask about that at various restaurants. The staff go and look at the labels for us to make sure that there is no corn in the food we want to feed her.
That sounds incredibly difficult... they put corn in EVERYTHING these days.
I read that even farm raised fish are being fed corn based feeds these days.
It is a bit difficult. For example, if we took her to a McDonald's for breakfast, there is corn in their hash browns and their pancakes, so she can have a biscuit or a cinnamon roll. Burger King has a macaroni and cheese kid's meal with fresh apple "fries" so that's usually what she wants if we get fast food for lunch or dinner. If she wants potato chips, then we have to find out what kind of oil the potato chips she eats were fried in, since corn oil causes a problem for her. Many pizza places use corn meal to keep the dough from sticking, but if we ask, the pizza place that is close to us will clean the area of corn meal and use wheat flour instead.
Luckily, we have not had to worry yet what the meat she eats has been fed, but she doesn't eat very much meat at all anyway.