Rank 1 now removes all rads from food and drinks. I don’t think this small benefit was worth 3 perks, but it’s fair for 1.
Rank 2 increases duration of food and non-alcoholic drink effects by 50%.
Rank 3 doubles the effects of all food and non-alcoholic drinks. Importantly, this does include survival mode! There’s a script that will fire a “second consumption” for the purposes of hunger, thirst, and caffeine. This does not actually modify Survival mode itself, instead just triggering the normal process a second time, so it’ll be compatible with any other changes to Survival mode.