They mostly like the associated taste sensations and associated satiety. As I understand it, there are separate taste receptors for fat and sugar - so it is probably better to say that humans desire some types of fat and sugar than to say that they desire calories.
And by the same token, it is probably even better to say that they desire ice cream and/or the taste of ice cream, and so on for other particular foods. The brain integrates information from the receptors you mentioned together with other taste receptors, smell receptors, texture sensations, and so on. Percepts and concepts are formed from the integrated total, and these frame the language of desire. Probably some of the best chefs and food critics do directly perceive, and savor, fat and sugar contents as such, but I doubt whether the same applies to all of us. Most of us are too distracted by the rich complex gestalt experience. This isn't to deny, of course, that our desires are strongly influenced by fat content.
It seems to me that you are not allowing enough slippage between two levels of explanation: what the genes want, and what the organisms want. Genes built our desires, but their "purposes" in doing so are not identical to those desires. Whereas, in the context of our conversation here, it would not be too wrong to say that humans' purposes are our desires.
By the way, I apologize if it sounded like I'm trying to oversimplify your position. In a (failed) economy of words, I figured it was OK to focus on one of the examples, namely a desire for fat.
As I understand it, there are separate taste receptors for fat and sugar - so it is probably better to say that humans desire some types of fat and sugar than to say that they desire calories.
And by the same token, it is probably even better to say that they desire ice cream and/or the taste of ice cream, and so on for other particular foods.
So: my position is that it is fine to talk like that - provided one makes the distinction between proximate and ultimate values. There's a pretty neat and general way of abstracting learning systems out into age...
The jacket text for Keith Stanovich's The Robot's Rebellion sums up the book well:
The book is an excellent introduction to the first stage of Yudkowskian philosophy: We are robots in a mechanistic universe running on a swiss army knife of cognitive modules. But at least we finally noticed we're robots, and we can use the skills of rationality to hop off our habit treadmills and pursue our values instead. These values are complex and often arbitrary, but we can use our reflective capacities to extrapolate our values based on "higher-order" desires, a desire for preference consistency, and other considerations. All this is argued for at length in Stanovich's book. The only thing missing is a discussion of what to do about all this when AI arrives.