Hippocrates De prisca medicina 8

[8] And if one would compare the diet of sick persons with that of persons in health, he will find it not more injurious than that of healthy persons in comparison with that of wild beasts and of other animals. For, suppose a man laboring under one of those diseases which are neither serious and unsupportable, nor yet altogether mild, but such as that, upon making any mistake in diet, it will become apparent, as if he should eat bread and flesh, or any other of those articles which prove beneficial to healthy persons, and that, too, not in great quantity, but much less than he could have taken when in good health; and that another man in good health, having a constitution neither very feeble, nor yet strong, eats of those things which are wholesome and strengthening to an ox or a horse, such as vetches, barley, and the like, and that, too, not in great quantity, but much less than he could take; the healthy person who did so would be subjected to no less disturbance and danger than the sick person who took bread or cake unseasonably. All these things are proofs that Medicine is to be prosecuted and discovered by the same method as the other.

[8] A consideration of the diet of the sick, as compared with that of men in health, would show that the diet of wild beasts and of animals generally is not more harmful, as compared with that of men in health. ¹ Take a man sick of a disease which is neither severe and desperate nor yet altogether mild, but likely to be pronounced under wrong treatment, and suppose that he resolved to eat bread, and meat, or any other food that is beneficial to men in health, not much of it, but far less than he could have taken had he been well; take again a man in health, with a constitution neither altogether weak nor altogether strong, and suppose he were to eat one of the foods that would be beneficial and strength-giving to an ox or a horse, vetches or barley or something similar, not much of it, but far less than he could take. If the man in health did this he would suffer no less pain and danger than that sick man who took bread or barley-cake at a time when he ought not. All this goes to prove that this art of medicine, if research be continued on the same method, can all be discovered.