Why eating out makes us fat... now with added Science!

In the past, I've commented on the fact that the decrease in home cooked meals in American households over the last few decades seems to be associated with the increase in our waistlines. Cutler, Glaeser and Shapiro provided an economic explanation for this: calories have become much cheaper (i.e. less prep time) and thus we consume more of them. While this reasoning is undoubtedly economically sound, it leaves a little to be desired from a biological perspective. You'd think we'd eat until we're full whether or not we ordered out or made it ourself...  a calorie is a calorie, right? (Not exactly, but close enough) Well, Jonah Leher has put together a hypothesis based on the fact that mice prefer food they have to work harder to obtain... and that obese people seem to feel less pleasure when they consume food (counterintuitive FTW!). I wonder whether the "harder to obtain" translates to "more expensive"...  I suspect it does... and, if so, would bet it does some of the work in explaining the socio-economic differences in obesity rates. Rich people may enjoy their food more... and thus consume less of it...  simply because they spend so much money on it.