AbD will do their best to accommodate. An example - I can’t eat cabbage. On the Japan AbD, there is a group meal stop at an okonomiyaki restaurant….okonomiyaki are basically cabbage pancakes with some mix-ins. I’d told the guides I would pass on eating while there; instead, they had spoken with the chef & arranged for one to be made for me with chicken and noodles. Another day, on the Osaka evening food tour, one of the guides on her initiative took the time to write out my food issues in Japanese for me so I could show it to the vendors, to be sure I didn’t inadvertently end up with something that might cause a problem.
If you have some destinations in mind, maybe reach out to AbD re the local food & possible GF options before you book.