My sister has PKU, which involves severe protein restrictions. so I
understand the challenges of traveling with this type of food
limitation. Disney does an admirable job of accommodating lo-pro guests, but you will have to do a bit of legwork yourself. As a first step, you should send an email describing
your situation, at least 14 days in advance of your trip, to
SpecialDiets@DisneyWorld.com.
A cast member will get back to you.
With any food issue, eating at table service restaurants is
easier. When you make your reservation for a table service meal, they
make a note on your file of your restrictions so that the staff can be
prepared in advance. A chef will also come out to the dining room to
speak with you to make sure they completely understand your needs.
Disney does carry some low and no protein foods that can be made at
table service venues with advance notice.
Eating counter service is, frankly, a more challenging. The counter
service places have a book of the labels of the food served, but it is
up to you to request the book and make your own determination before
ordering. When eating at restaurants with my sister, we tend to stick
with items that we know will be low-protein: fresh fruits and veggies,
French Fries, ices, etc. To map your plan in advance, you should go to
the website allears.net and search on the word "menu." You will find
menus for almost every restaurant at WDW and find the ones that feature
safe items. I suspect that you will need to supplement your wife's
food. It is 100% acceptable to bring food items into the parks.
I urge you to take a look at resources such as the pkunews.org and
Michigan-pku.org which have articles about tips for Disney travel.
Another resource is a book called PassPorter's Open Mouse for Walt
Disney World.
Good luck with your planning. Please feel free to ask additional questions.