Hebrews 12:10
7 Let us not then fatten the body, but listen to Paul saying, “Make not provision for the flesh, to fulfill the lusts thereof,” As if one should take food and throw it into a drain, so is he who throws it into the belly: or rather it is not so, but much worse. For in the one case he uses the drain without harm to himself: but in the other he generates innumerable diseases. For what nourishes is a sufficiency which also can be digested: but what is over and above our need, not only does not nourish, but even spoils the other. But no man sees these things, owing to some prejudice and unseasonable pleasure.
Do you wish to nourish the body? Take away what is superfluous; give what is sufficient, and as much as can be digested. Do not load it, lest you overwhelm it. A sufficiency is both nourishment and pleasure. For nothing is so productive of pleasure, as food well digested: nothing so [productive of] health: nothing [so productive of] acuteness of the faculties, nothing tends so much to keep away disease. For a sufficiency is both nourishment, and pleasure, and health; but excess is injury, and unpleasantness and disease. For what famine does, that also satiety does; or rather more grievous evils. For the former indeed within a few days carries a man off and sets him free; but the other eating into and putrefying the body, gives it over to long disease, and then to a most painful death. But we, while we account famine a thing greatly to be dreaded, yet run after satiety, which is more distressing than that.
Whence is this disease? Whence this madness? I do not say that we should waste ourselves away, but that we should eat as much food as also gives us pleasure, that is really pleasure, and can nourish the body, and furnish it to us well ordered and adapted for the energies of the soul, well joined and fitted together. But when it comes to be water-logged by luxury, it cannot in the flood-wave, keep fast the bolts themselves, as one may say, and joints which hold the frame together. For the flood-wave coming in, the whole breaks up and scatters.
“Make not provision for the flesh” (he says) “to fulfill the lusts thereof.” He said well. For luxury is fuel for unreasonable lusts; though the luxurious should be the most philosophical of all men, of necessity he must be somewhat affected by wine, by eating, he must needs be relaxed, he must needs endure the greater flame. Hence [come] fornications, hence adulteries. For a hungry belly cannot generate lust, or rather not one which has used just enough. But that which generates unseemly lusts, is that which is relaxed by luxury. And as land which is very moist and a dung-hill which is wet through and retains much dampness, generates worms, while that which has been freed from such moistness bears abundant fruits, when it has nothing immoderate: even if it be not cultivated, it yields grass, and if it be cultivated, fruits: [so also do we].
Let us not then make our flesh useless, or unprofitable, or hurtful, but let us plant in it useful fruits, and fruit-bearing trees; let us not enfeeble them by luxury, for they too put forth worms instead of fruit when they have become rotten. So also implanted desire, if you moisten it above measure, generates unreasonable pleasures, yea the most exceedingly unreasonable. Let us then remove this pernicious evil, that we may be able to attain the good things promised us, in Christ Jesus our Lord, with whom to the Father, together with the Holy Spirit, be glory now and ever and world without end. Amen.
Source: Homilies on the Epistle to the Hebrews (New Advent)