So, although I haven't managed to find the relevant federal labeling regulations, my understanding is that "modified food starch" will turn out to come from potatoes about 1/4 of the time. I discovered this after getting sick from some tortilla shells and wondering about the modified food starch. I don't know exactly what my allergens are -- most allergies are to proteins, but if a corn allergy gets triggered by corn syrup, it makes sense that a potato allergy can be triggered by starch. Maybe traces of protein stick around, or maybe I'm allergic to other components.
Anyway, I thought I'd make a list of stupid places I have found modified food starch:
- tortilla shells - most pre-grated cheese - certain types of donuts (further research is required on whether there's anything predictable to this) - jelly beans
Has anyone else had experiences with this?
 Potato starch may get turned into dextrin and maltodextrin. I have no idea if these ever contain allergens.