I would not like to see this implemented if it required inventory management. You don't worry about food for your soldiers, or your scientists, so I don't think it should be a concern with the aliens. (I think the level of inventory management is already complex, bordering on tedious. If I had designed UFO, I would have avoided inventory management for clips of ammunition for handheld weapons too - or at least partially automated it.)
I can see where you're coming from though, and it would certainly be more realistic. And I do like the idea that a captured Alien would starve to death if you were unable to provide it with food. It does add a degree of urgency to interrogation early in the game.
But once you do complete research on alien food, I don't think it should show up as an inventory item – certainly not one that you have to manage. Feeding of the aliens is just taken care of in the background instead.
I look at it this way: my job in the game is to manage all military assets and inventory, and there is probably an administrator there who worries about food, toilet paper, weekend employee events at Disneyland, and stuff like that. :-) .. And, compared to a (huge) military budget, it's just not enough to be worth worrying about. (Especially if we have a resident chef out back, quietly soylent-greening expired soldiers.)