Plato The Republic Book IX.
Again, hunger and thirst are inanitions of the body, ignorance and folly of the soul; and food is the satisfaction of the one, knowledge of the other. Now which is the purer satisfaction—that of eating and drinking, or that of knowledge? Consider the matter thus: The satisfaction of that which has more existence is truer than of that which has less. The invariable and immortal has a more real existence than the variable and mortal, and has a corresponding measure of knowledge and truth. The soul, again, has more existence and truth and knowledge than the body, and is therefore more really satisfied and has a more natural pleasure. Those who feast only on earthly food, are always going at random up to the middle and down again; but they never pass into the true upper world, or have a taste of true pleasure. They are like fatted beasts, full of gluttony and sensuality, and ready to kill one another by reason of their insatiable lust; for they are not filled with true being, and their vessel is leaky (Gorgias). Their pleasures are mere shadows of pleasure, mixed with pain, coloured and intensified by contrast, and therefore intensely desired; and men go fighting about them, as Stesichorus says that the Greeks fought about the shadow of Helen at Troy, because they know not the truth.