Of course, when offered tasty, calorie-rich food instead, my boys stuff their faces with it - and they eat the parts first that are richest in calories and / or protein. Rats are not stupid, and they live in packs, usually - so if rat A does not devour the best parts first, rat B will eat them instead while silly rat A is gnawing on not-so-rich food.

Ain't gonna happen
No, no, no, you're misinterpreting this completely. You're starting from the assumption that rats (or children, or smokers, or people in general) have any intelligence. This has now been
proved to be completely wrong. It's like the Ptolemaic system in astronomy - intelligent people believed in it, but then Copernicus came along, flipped the whole thing inside out, and everything became much simpler.
There is no such thing as intelligence. What people mistake for intelligence is just a manifestation of the fifth fundamental force of nature: like magnetism, it draws living things irresistibly towards things containing Addictium. (Evidence is emerging that the Ptolemy cunningly stuffed large quantities of Addictium into his theory, the sneaky b*st**d - this is why people believed in it for so long). So what's actually happening with your rats is:
1. Rat A goes for the Oreo-centre, drawn in by the Addictium contained in it.
2. Oreo-centres are singularities ripped in the fabric of space-time by concentrations of Addictium beyond our imagination. That much Addictium simply cannot exist in one Universe - thus the laws of the Universe are suspended. The outside parts of the Oreo are the event horizons: once you take them off and your eyes behold the naked singularity, there's no going back. (To conceal the true, sinister nature of these Irresistible Black Holes of Evil, Big Sugar cunningly colours them
white).
2. As Rat A approaches the Oreo, tidal forces in the titanic Addictial field emanating from the Oreo tear apart its brain structure, causing it to think it might be quite enjoying this.
3. The total collapse of Rat's A's brain-structure under the Oreo-influence gives off a deadly cloud of high-energy (8 YeV) particles called
addictons. Nobel prizewinner Peter Higgs speculates that addictons are made up of quarks of flavour Gloopy, JazzFunk and CherryMint, but needs a bigger collider to prove this.
4. Their brains hopelessly irradiated by addictons, Rats B, C and so on are drawn into the sphere of influence of the Oreo, thinking "I want a part of this!", only to fall hopelessly beyond the event horizon into the gaping maw of the singularity, eventually emerging elsewhere in the space-time continuum as giant babies. (Or was that last bit in a film I saw once?)
This also explains scientifically why one person, anywhere, smoking or doing something that looks a bit like smoking, constitutes a public-health disaster worse than the Black Death.
[Philosophy Break Time!
If one child eats one Oreo in a forest, but there are no "scientists" to observe it, is the child addicted to Oreos?
Free pack of Oreos for the best answer!]