If you have stringent dietary requirements, you should plan to self-support and bring your own food as much as possible. If the rest stops happen to have something that is friendly to your body, great. If not, you can't rely on it. My ex had a list of food allergies a mile long and for him to chance it and hope that there was something that he could eat was asking for trouble.

I do think it's unusual for a rest stop to offer fatty/meaty food for a bike ride.