No, since (as someone pointed out elsewhere in this thread), a gram of sugar has less than half of the calories in a gram of fat. If Alice and Berta both choos

No, since (as someone pointed out elsewhere in this thread), a gram of sugar has less than half of the calories in a gram of fat. If Alice and Berta both choose to consume exactly 2000 calories a day, but Alice chooses a low-fat diet while Berta chooses a low-carb one, then Berta will pay less according to that system. So it's not really a problem that sugar costs less; low-fat diet are still cheaper.