I don't know the answer to this, but I'd caution against using lab rats, which, keep in mind, have quite different dietary needs, as an indicator of human dietary preferences.

Well you are capable of estimating some probabilities, no? I agree that caution is in order, but I feel pretty confident, perhaps 90% probability, that lab rats will choose pizza over oatmeal.

Here's a study which might affect your probability assessments:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0060407

Exposure to a palatable diet had long-term effects on feeding patterns. Rats became overweight because they initially ate more frequently and ultimately ate more of foods with higher energy density.