Beer-Battered Tuna Sandwich  

As long as the food is in your top inventory slot, the stats last until the food is consumed. Once you eat it, the stats are gone. What a lot of people do, is keep a stack of cheap food (foraged stuff, or rations) in a lower slot and force feed themselves the non stat food, essentially making the stat food last forever.

It seems counter intuitive, but the stats are there before you eat it, not after.