In Robert Sheckley’s story Dimension of Miracles*, the sentientPrize , although it occasionally eats orithi and other aesthetic foods, subsists mainly on itself. When the hero, Carmody, objects that this can’t be true – eventually he’d eat all of himself, the Prize returns that, every timre he eats some of himself, there’s less to feed.
Assuming that the Prize didn’t undergo amputations trauma, and could somehow consume itself without other injury, it makes sense – to a point. There must be a certain irreducible minimum below which the organism can;t function.
ncidentally, I don’t think King’s hero is trying to prolong his life by a reasoned use of himself as resourcews – i just think he’s hungry.
*A novel that I and others have long suspected inspired Douglas adams’ The Hitchiker’s Guide.