You're overthinking this and causing some kind of weird double negative. You're asking for active user input - in order to deselect - what the user doesn't want. That is a very confusing anti-pattern.

Just have the user actively select what they want to avoid from a plain list (no pre-checked boxes).

Select the proteins you want to avoid:

[_] Beef

[_] Chicken

[_] Pork

You're overthinking this and causing some kind of weird double negative. You're asking for active user input - in order to deselect - what the user doesn't want. That is a very confusing anti-pattern.

Just have the user actively select what they want to avoid from a plain list (no pre-checked boxes).

^{download bmml source – Wireframes created with Balsamiq Mockups}

Another solution might be to have dropdown menus which make it more explicit what is being selected:

^{download bmml source}