A total efficiency value is calculated for crews for any given action based on the class and traits applicable to the action, as well as on the food reserves present. Certain modifiers are not further modified by food and station efficiency, they are: inventory volume & mass efficiency and propellant efficiency (trip durations are already penalized based on reduced food stores).
Implementation:
Total bonus calculations are further modified by this efficiency, i.e.:
Eff = ClassEff * StationEff * FoodEff * (1 + TraitEff)