The simplest way to determine if food gives RAtt or not is to look it up on a site such as
wiki.
I really doubt that you will find a food with RAtt that is not already on the list. If you do think you have such a food, try RAtt'ing some DC+ mobs with and without the food to see if there is a statistical difference. If there is, you can play with the RAtt formulas, switching gear around, etc, to determine what the bonus is.