Bread As A Protein Food

Even the homely but much depended upon article of diet, bread, has a goodly proportion of protein, 12 to 16 per cent.

(See table, chapter V (How Much Fuel?).) But as ordinarily eaten with butter, marmalade or jelly it descends greatly in the scale as a protein food. For example, one slice of whole wheat bread equals 100 calories, of which 15 calories are protein. Adding to this 50 calories of butter, the total food value becomes 150; the protein calories still 15 makes the relation of protein to the total just 10 per cent. Foods served in this way may be most excellent foods, but if every dish is so prepared that it contains 10 per cent or less protein it is quite evident that there is great danger of the protein intake being too low unless the entire food ration be kept high, which might in many cases make the total more than necessary for body needs.

Then too it must be remembered that many foods, as fruit, desserts, sweets, etc., contain practically no protein so that somewhere in the daily ration there must be food containing much more than 10 per cent protein.

The Brain Worker

A farmer who needs from 3000 to 3500 food units daily, or perhaps more, easily gets his necessary protein even while living on medium and low protein foods. He uses up the excess of carbohydrate and fat in the energy he expends in his active labor; but the one who needs, because of a sedentary life, to be careful not to overeat must take the more highly protein foods. Brain workers, or those who expend nervous rather than muscular energy, need a comparatively high protein ration with a low total intake. They must live on the higher protein foods.

The Convalescent

A person convalescing from a wasting disease must have ample protein to rebuild tissue, but often his digestive organs are not equal to the task of caring for a total amount of 2000 or more calories. So the diet for such a one must be so planned that the proportion of the tissue building elements be high in order that enough of this may be supplied even though the entire daily intake must of necessity be lower than normal.

If You Are Too Thin

Many thin people would gain in weight more readily on a diet supplying a goodly amount of protein, with less of the carbohydrate and fat and even a low total daily ration, than on one in which the entire food intake is pushed to an extreme degree, imposing an extra tax on the digestive organs in their effort to care for an excessive amount of food material which never can be gotten ready for absorption and utilization by the tissues.

Complete Proteins

There is another important phase of the protein question that must be considered. We have referred in chapter II (The Body As A Stove. Metabolism) to the complex structure of proteins and to the fact that complete proteins contain some seventeen nitrogenous combinations called amino-acids. These seventeen parts may be arranged in many different ways to form various kinds of body tissue. Proteins, in order to repair every kind of tissue, must contain all of these seventeen units and such proteins are said to be complete.

Quality As Well As Quantity

There are other proteins in which some of these important combinations of nitrogen, or "building stones," are missing and so are incomplete. Some of the important amino-acids are, tyrosin, trytophan, leucin, lysin, glycocoll, cystin, histidin, and arginin.

It is quite evident then that all proteins are not of equal value to the body and that a diet may be deficient in the quality of its protein as well as in the quantity. While this question is not yet well understood, yet as the result of animal experimentation something of the nature of the various food proteins has been ascertained. For example, it has been shown that some proteins will maintain but will not induce growth. Rats fed on corn fail to grow, but develop properly if their diet is supplemented by casein of milk, egg yolks, the proteins of other grains as the glutenin of wheat, glycenin from the soy bean, globulin from squash seed, globulin from cotton seed, excelsin from Brazil nuts, and globulin from maize or corn.*

Grain Proteins

It has been found that an animal does not thrive if fed on a single cereal grain even though the amount of protein be theoretically correct and the total food units be sufficient. This seems to be due, in part at least, to the fact that many of the grain proteins are incomplete. This does not mean that grains are not good foods, but simply that the diet must be varied enough so that incomplete proteins may be supplemented by complete proteins or with proteins supplying the missing links.

♦Quoting from L. B. Mendal, who has done much work along this line: "When the gliadin of wheat, a prominent protein of this seed, is fed as the sole protein, adult animals are suitably maintained; but growing animals cease to increase in body weight, remaining in nutritive equilibrium without growth unless the amino-acid lysin is added to the gliadin food. Thereupon growth is promptly resumed. The explanation becomes apparent in the fact that gliadin is almost entirely devoid of the amino-acid lysin; and inasmuch as this is obviously needed for new protein construction, growth can not proceed until the missing unit is supplied. Again zein, the most conspicuous protein of the maise kernel, fails to yield either lysin or tryptophan or glycocoll, and accordingly is entirely inadequate to meet the nitrogenous needs of the animals in respect to either maintenance or growth. It may be fed in the greatest abundance, yet the animals decline in health unless the zein is supplemented by some more perfect protein. If the amino acid tryptophan is added to the imperfect maise, protein maintenance of body weight without growth is promptly established. . . . If both tryptophan and lysin are added to the zein, the diet thereupon becomes suitable for growth." - Journal of American Medical Association, Sept. 5, 1914.