Obviously, that wouldn't work. I find this unconvincing. After all, the biotic food chain requires such a common denominator, otherwise one kind of creature would be incapable of ingesting another. The metabolism of plants, animals, and man, based on the same biochemical principles, had to be similar, and therefore key metabolic pathways would employ similar macromolecules. I think therefore that Gish had already answered your question.
Gish mentions sugars above.