Food stuffs as found in nature or prepared for the market are, with few exceptions, neither pure nor, for practical dietetic purposes, composed of a single organic nutrient, aside from water and inorganic nutrients and waste.

Roughly speaking, the mixed, solid and, in common parlance, dry food stuffs of an ordinary dietary, consist of about 50% of organic nutrients - protein, fat and carbohydrates - and 50% of water, salts, cellulose and other indigestible waste.

Since the standard minimum diet for an adult at light exercise consists of about 50 grams of protein, 50 of fat and 400 of carbohydrates, a total of 500 grams, the daily ration consists of about 1 kilogram (2.2 lbs.) of solid food stuffs. Since fats yield the greatest number of calories in proportion to their weight, the most concentrated ration contains the maximum of fats. Even allowing for the ingestion of 150 grams of fats, which can scarcely be digested and absorbed without considerable waste, about 250 grams of proteins and carbohydrates, which have nearly the same calorific value, must be given. Thus the total weight of condensed nourishment is 400 grams and this amount cannot be compressed into a less volume than about 400 c.c, or nearly a pint.

Hence the popular and pseudo-scientific allusions to nourishment by compressed tablets are based on a gross misconception.

Theoretically - and to a considerable degree, practically - it is obvious that if we confine our attention to organic nutrients, protein, fat and carbohydrate, and ignore indigestible waste and inorganic nutriments, as well as inappreciable amounts of organic nutrients, all food stuffs may be divided into seven groups, as follows:

C. Food stuffs of all three ingredients: protein, fat and carbohydrate.

A. 1. Food stuffs consisting of protein alone. The white of an average egg weighs 30 grams and contains 20% of protein, 6 grams in all. Oysters, if the liver is eliminated or if no nourishment has been imbibed, contain 5% of protein, much less than is commonly supposed. Eight or nine egg whites or 1 kilogram of oysters would furnish the minimum protein ration.

Expressed meat juice, cooled and skimmed to remove the fat, contains about 6% of protein, about the maximum contained in any liquid meat preparation.

Beef tea is practically devoid of nutriment, except for small amounts of gelatin, and for coagulated protein in suspension. It contains stimulant and toxic extractives and is similar in dietetic value to urine.

Artificial protein foods include those manufactured from meat, those from vegetable albumin, as from the residue of rape seed from which the oil has been expressed. This residue was formerly used merely as feed for live stock. Thirdly, casein preparations, sold under various trade names. The last two kinds of artificially prepared protein are concentrated and may be valuable additions to a diet for persons of weak assimilation. Such preparations are usually nearly tasteless.

Meat extracts of the Liebig type contain about 1 part in 2000 of protein and are to be classed with beef tea made at a temperature near enough the boiling point to coagulate albumin, and with urine.

Valentine's meat juice contains 0.44% of albumin; Starr's 1.10%; Benger's 1.11%; Johnston's 1.17%. (A. H. Chester.)

Peptonized meat extracts consist mainly of albumoses, true peptone being bitter and toxic. Somatose, a granular predigested meat powder contains about 90% of albumoses.

In using any of the proprietary meat extracts or combinations of meat and vegetable nutriment, the stated dose must be ignored, allowance must be made both for the nutritive and toxic effect of any alcohol present (usually about 20%) and the nutritive content must be estimated according to authentic, impartial analyses. These preparations can not be used for exclusive, complete physiologic nutrition, and the best of them scarcely exceed milk or expressed beef juice, respectively, in protein value.

A, 2. Food stuffs consisting of fat alone. Solid fat meat, as fat pork, mutton and beef fat, contains about 80% of chemically pure fat, the remainder being mostly water. There is about 1% of protein, but in the form of connective tissue which, though delicate, is scarcely digestible.

Lard, suet and tallow consist of about 85% of pure fats, butter and oleomargarine - which latter is nearly as valuable, though the waste of fat is proportionate to its solidity or, inversely, to its melting point - of about 90%. Olive oil and its substitutes, such as cotton seed oil, peanut oil, etc., contain about 98% of pure fats. Not counting waste in the intestine, which is always considerable if they are given unmixed and in any considerable quantity, these oils yield about 9 calories per c.c.

Cod liver oil contains biliary salts, which facilitate the absorption of fats, but it also contains various excrementitious substances, some iodine and, often, products of decomposition. Except the rather dubious presence of antitoxic or antibacterial substances, it has no greater value than other oils, and it has obvious disadvantages aside from the repugnance of the patient. The need of artificially supplied biliary salts is not established in most of the cases in which cod liver oil is commonly given, and, if demonstrated, these salts may be administered pure or nearly so.

Hence, at present, the wide use of cod liver oil rests on traditional value. Like pepsin, it may be almost entirely eliminated from medical use.

The relatively enormous waste of fats and oils when given in large quantity - over 100 to 150 grams a day - must be borne in mind, also the small absorbability of fats of high melting point, and the cathartic action in preventing the utilization of other foods.

A. 3. Food stuffs consisting of carbohydrate alone. Commercial white sugar consists of about 98% of pure saccharose and, so far as it can be used without producing fermentation and irritation of mucous membranes, it is one of the most assimilable, and both physiologically and commercially, oeconomic foods. It is used, without harm by persons in health, to the amount of 100 - 150 grams a day, furnishing about 450 - 600 calories, or 1/5 - 1/4 of the total needed, at an expense of about 1 - l 2/3 cents a day. Brown sugar is about 97% pure and is relatively more oeconomic. Plain candy contains about 80% of sugar, the water present being physically water, as the molecule of saccharose does not take up water of crystalization. Concentrated white and maple syrups contain about 55%-. of saccharose. The sugar of the sugar cane, sugar beet and sweet maple is identical, so that adulteration is purely a commercial and not a hygienic fraud. Glucose may be considered as nearly pure, predigested carbohydrate, and, if used in moderation, there is no physiologic objection to it. Laevulose is prepared for diabetics at considerable expense. It can be utilized only to the amount of 20 - 30 grams, even by a healthy person, without producing glycosuria. Milk sugar is of especial value in feeding infants. Other sugars, though obtainable, are not used in diet.

Tapioca, sago, arrow root and corn starch are nearly pure starches, (95 - 98%).

B. 1. Food stuffs consisting of protein plus fat are limited to meats in general, egg yolk, certain cheeses. A few nuts contain a very little carbohydrate.