[meowface]

Some people are allergic to so many things, with such sensitivity, that nearly all foods contain some percentage of something they're allergic to (even if it's only trace amounts). In that case, consuming nothing but water effectively assures a food allergy-free experience for the duration of the fast. If they're allergic to things found in water as well, then I'm not sure what the best solution is.

[bodhibyte]

I actually drink distilled or deionized water during my fasts. This is what was available on my first long fast and I've done it since.