I don't mean that I can't buy food. I mean that I can't trade between dollars and calories. For example, a scoop of premium ice cream costs me $1.25 and 250 c

I don't mean that I can't buy food. I mean that I can't trade between dollars and calories. For example, a scoop of premium ice cream costs me $1.25 and 250 calories. The currencies are independant and inexchangeable; if there was an exchange rate between them, I could get that same food for $5.00 and 50 calories. Any food I contemplate has a cost somewhere in dollar-calorie space, so the currency with which I buy food can be accurately modeled as a two dimensional vector space (or perhaps as the complex numbers, though I guess I don't really use the field properties...).