In ancient Borne (as Cato records) the principal citizens had their large vegetable gardens near the city, the same being cultivated by the owners themselves, some among whom derived their family names in this way as successful specialists; such as Piso from the Pea, Cicero from the Vetch, Fabius from the Bean, and Lentulus from the Lentil. The chief value of vegetables as food lies in the mineral salts which they contain abundantly; these are combined with much water, but quite sparingly with proteid nourishment available for bodily repair; their framework consists altogether of cellulose. Greens, and Savoys afford most nitrogenous matter; whilst, together with Leeks, Cabbage, Turnips, Salsify, and Carrots, they are endowed with carbohydrates, and mineral salts. But the effect of cooking upon green vegetables, as it is generally practised, serves only to reduce their already poor stock of nutrients. As a whole such vegetables are not readily digested by the stomach, and when reaching the intestines their bulk makes them difficult to be assimilated; if they are at all stale, then discomfiting fermentation takes place, engendering noxious gases, and provoking troublesome flatulence, with distension.

To be wholesome vegetables should always be eaten as fresh as possible; their main use is as a source of mineral salts, particularly those of potash, which keep the blood supplied with alkaline elements, and thus lower the acidity of the urine; so that vegetable foods are to be especially advised for persons liable to gravel, (except garden Rhubarb, Sorrel, and Tomatoes, because of their oxalic acid). Vegetable feeders require relatively more table salt with their food than mixed feeders, particularly with Potatoes, so as to neutralize chemically such excess of mineral salts as might otherwise be prejudicial; for this reason herbivorous animals crave for common salt, but not so the carnivorous animals. For gouty, or rheumatic persons the acidity of the urine can be certainly kept in check by a free use of green vegetables, and of such other foods as contain alkaline salts of potash; but at the same time the diet must not be too poor in proteids. As for the vegetables, they are not to be cooked in a deluge of water, else this, when thrown away before serving, will carry with it most of the soluble alkaline salts which should serve to neutralize the acids of digestive fermentation.

Green fruits (uncooked), and raw vegetables disturb the stomach and bowels, because the starch which they contain cannot be acted upon by the saliva during mastication when these foods are unboiled; then, on their reaching the stomach, the gastric juice cannot gain access to their structure so as to digest the albuminoid constituents, therefore the substances remain ill-digested, and troublesome sour fermentation is the result.

That cooking increases the digestibility of things eaten at table is true only with respect to vegetable foods, whilst that of animal foods is diminished rather than increased by cooking. But the flatulence which so often occurs after taking a meal of cooked green vegetables, particularly of Cabbage, does not similarly happen if we eat practically the same green vegetables in the form of plain salads uncooked; therefore it must be the cooking process which then gives rise to this obnoxious difference, that is, through the splitting-up effect of the heat, and the fermentation of the carbohydrates (starch, sugar, and fat) induced by cooking, when a formation of fermentative acids, and gases occurs (chiefly carburetted, phosphuretted, and sulphuretted hydrogen) in the system. Vegetable foods, unless eaten in large quantities, will not afford a sufficiency of proteid nourishment to the body; and what proteid food is present in vegetables has its value lowered in many cases by the difficulty with which it is utilized therein. Furthermore, the nitrogenous essentials of bodily nourishment can be obtained in the needful concentrated state only from animal foods, these essentials making for nervous energy, and intellectual capacity, as well as for power to resist disease.

Meat, fowl, and fish are concentrated forms of nitrogenous proteid nourishment. Then, again, a purely vegetable diet must of necessity be bulky, because so much water is included therein, particularly when cooked, and so much unassimilable cellulose is bound up therewith; whilst the limited amount of proteid sustenance present is diluted by a disproportionate quantity of starch. If boiling water is poured upon the starch grains they swell up, and burst, so that the true starch escapes from between the layers of cellulose. It is this rupture of the starch grains which is sought to be effected by the proper cooking of vegetable foods. The mineral constituents of most vegetables increase the solubility in the system of certain gouty salts (bi-urate), but the mineral constituents of meat tend to diminish this solubility. Dr. Luff, a practised experimentalist, gives the first place in this direction to Spinach against a gouty habit of body; Brussels Sprouts, and French Beans come next on his list, being followed by Cabbage, Turnip-tops, Turnips, and Celery. It is now understood that vegetables and plants obtain the mineral salts, and earth salts on which they depend for their nourishment, through the agency of (microscopical) organisms known as nitro-bacteria; these attack the surface of rocks wherein potash, and iron are contained, and disintegrate in a similar way all dead organic matters, dead animals, dung, etc., dissociating the compact atoms, and thus producing nitrates, whereby the foundation of all fertility is laid.

Thomas Tryon (Way to Health, 1650) wrote: "Raw herbs are a sublime kind of food, and are to be preferred to that which is boiled, for the pure volatile spirit in the herbs cannot endure the violence of the fire, but in boiling a great part of this is evaporated. For which cause boiled herbs lie heavier, and colder in the stomach than do raw herbs, which is scarcely believed by many persons. For, they that love boiled herbs do generally eat much flesh with them, and so cannot discern the operation these have." "The strength, and comforting quality of everything consists principally in the spirituous parts, which are lost by evaporation in the boiling, and therefore the substance becomes of quite another nature. That lively tincture, and spirituous part which it possessed whilst raw, can never be recovered by all the ingredients which nature, or art can afford. Do not all creatures eat their herbs raw? and are they not admirably sustained thereby?"