Ask the restaurant. Also be careful about the possible contamination with gluten if the fries are cooked in pre-used frying oil. Also, some flavoring can contain gluten. I've removed casein and gluten from my child's diet and she still seems to be allergic to foods. First, check to make sure no hidden casein or gluten could be present.
Some individuals are also allergic to soy and corn.
Try eliminating these one by one from the diet. Inc. All rights reserved.