His impulse toward vegetarianism, however, is based on his instincts and his principles rather than on any actual experience of poor health.

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To him the simplest fare is the best, and the consumption of animal flesh is a moral debasement that far fewer would indulge in if they had to slaughter beasts themselves.

Henry David Thoreau
Spark Notes: Baker Farm & Higher Laws

Bread and water produce the highest pleasure, when one who needs them puts them to his lips. To grow accustomed therefore to simple and not luxurious diet gives us health to the full, and makes a man alert for the needful employments of life, and when after long intervals we approach luxuries, disposes us better towards them, and fits us to be fearless of fortune.

—Epicurus, LETTER TO MENOECEUS

It is also necessary to accustom the body to become alienated, as much as possible, from the pleasure of the satiety arising from luxurious food, but not from the fullness produced by a slender diet, in order that moderation may proceed through all things, and that what is necessary, or what is most excellent, may fix a boundary to our diet. For he who thus mortifies his body will receive every possible good, through being sufficient to himself, and an assimilation to divinity.

—Porphyry, On Abstinence From Animal Food, Book 1

Hence, to be purified from all these is most difficult, and requires a great contest, and we must bestow much labour both by night and by day to be liberated from an attention to them, and this, because we are necessarily complicated with sense. Whence, also, as much as possible, we should withdraw ourselves from those places in which we may, though unwillingly, meet with this hostile crowd. From experience, also, we should avoid a contest with it, and even a victory over it, and the want of exercise from inexperience.

…

He also adds, that this philosopher does not even dream of betaking himself to banquets. Much less, therefore, would he be indignant, if deprived of broth, or pieces of flesh; nor, in short, will he admit things of this kind. And will he not rather consider the abstinence from all these as trifling, and a thing of no consequence, but the assumption of them to be a thing of great importance and noxious? For since there are two paradigms in the order of things, one of a divine nature, which is most happy, the other of that which is destitute of divinity, and which is most miserable ¹⁶; the Coryphaean philosopher will assimilate himself to the one, but will render himself dissimilar to the other, and will lead a life conformable to the paradigm to which he is assimilated, viz. a life satisfied with slender food, and sufficient to itself, and in the smallest degree replete with mortal natures.

…

So that only granting to nature what is necessary, and this of a light quality, and through more slender food, he will reject whatever exceeds this, as only contributing to pleasure.

…

For, let any man show us who endeavours as much as possible to live according to intellect, and not to be attracted by the passions of the body, that |37 animal food is more easily procured than the food from fruits and herbs; or that the preparation of the former is more simple than that of the latter, and, in short, that it does not require cooks, but, when compared with inanimate nutriment, is unattended by pleasure, is lighter in concoction, and is more rapidly digested, excites in a less degree the desires, and contributes less to the strength of the body than a vegetable diet.

—Porphyry, On abstinence from animal food (1823) Book 1. Pp.11-44

Let all persons of all conditions avoid all delicacy and niceness in their clothing or diet, because such softness engages them upon great misspendings of their time, while they dress and comb out all their opportunities of their morning devotion, and half the day’s severity, and sleep out the care and provision for their souls.

—Rev. Jeremy Taylor, CARE OF OUR TIME. -Rules for employing our time…, The Whole Works of the Right Rev. Jeremy Taylor, Volume 3. THE RULE AND EXERCISES OF HOLY LIVING AND DYING….: The Rule and Exercises of Holy Living and Dying

For besides hunger and thirst, there are some labours of the body, and others of the mind, and there are sorrows and loads upon the spirit by its communications with the indispositions of the body ; and as the labouring man may be supplied with bigger quantities, so the student and contemplative man with more delicious and sprightful nutriment : for as the tender and more delicate easily-digested meats will not help to carry burdens upon the neck, and hold the plough in society and yokes of the laborious oxen ; so neither will the pulse and the leeks, Lavinian sausages, and the Cisalpine suckets or gobbets of condited bull’s-flesh, minister such delicate spirits to the thinking man ; but his notion will be flat as the noise of the Arcadian porter, and thick as the first juice of his country lard, unless he makes his body a fit servant to the soul, and both fitted for the employment.

—Rev. Jeremy Taylor, The House of Feasting .The Whole Works of the Rt. Rev. Jeremy Taylor, Volume 1

But her innocence left her a very long time ago, and she never noticed. She eats only grass, but she has a meat eater’s heart.

—Tove Jansson, The True Deceiver

All this is contrary to nature, for the Creator has ordained the same natural way of life for both us and the animals. ‘Behold,’ says God to man, ‘I have given you every herb of the field, to serve as food for you and for the beasts’ (cf. Gen, 1:29-30). Thus we have been given a common diet with the animals; but if we use our powers of invention to turn this into something extravagant, shall we not rightly be judged more unintelligent than they? The animals remain within the boundaries of nature, not altering in any way what God has ordained; but we, who have been honored with the power of intelligence, have completely abandoned His original ordinance. Do animals demand a luxury diet? What chefs and pastry-cooks pander to their bellies? Do they not prefer the original simplicity, eating the herbs of the field, content with whatever is at hand, drinking water from springs – and this only infrequently?

Since, then, possessions are the cause of great harm and, like a source of disease, they give rise to all the passions, we must eliminate this cause if we are really concerned for the well-being of our souls. Let us cure the passion of avarice through voluntary poverty. By embracing solitude let us avoid meeting those who do us no good, for the company of frivolous people is harmful and undermines our state of peace. Just as those who live in an unhealthy climate are generally ill, so those who spend their time with worthless men share in their vices. 

—St. Neilos The Ascetic
Philokalia