I’m on the NZ AbD right now. We have some gluten free, a nut allergy, vegetarians, and at least two others with different food sensitivities or intolerances. The guides are working with each group meal provider to ensure there are options for everyone, even in the cooking class, and separate plates are prepared as needed when food is served family style. In addition, many restaurants have menus labeled options for vegan or gluten free. I’ve seen servers point out specific dishes with ingredients either OK to eat or which to avoid as needed.
As
@sayhello noted above, it will likely vary based on country or city how many options might be available. You could always reach out to AbD with questions re options at a specific destination; for the more established adventures, they likely have experience with gluten free guests.