The food and drink systems are less about realism and more about RP. We want the world to be believable, as far as fantasy worlds go, but not necessarily "realistic," where "realism" is defined as a style applied to fiction and gaming.
In fact, it used to be that you had to eat and drink IG a lot more often, and the food did even less to quench a person's appetite than it does now. We changed it because the effect was more annoying/distracting than it was useful in establishing a "suspension of disbelief."
I hope that makes sense. If not, I suspect Dorg or Darkstorme (or even Carillon) may be able to better explain the move away from more frequent requirements for PCs to eat and drink.