THE FOOD WE EAT.

Manawatu Herald, Volume XLIII, Issue 2336, 1 October 1921, Page 4

THE FOOD WE EAT.

POINTS ON ENERGY VALUE,

TYPICAL FOODS REVIEWED

(By Professor Worley.) It is common knowledge that different foods differ widely, not only in their cost, but also in their nutritive value, and it would appear possible to express numerically the actual, or at least the relative, nutritive values of equal weights of different kinds of food. The fact must not be overlooked, however, that human food requirements are-highlv complex, that the complete normal food of mankind contains a large number of essential constituents. These have previously been broadly classified/ but it is natural that attention should first be directed to the energy or heat values of various kinds of food. These latter are generally known ns food values, but are really fuel values, and are comparable' with the values that might be given of wood, mineral oils, and different coal for steam raising purposes. In order to understand the meaning of food values and the method whereby they are measured, it is necessary to have some idea of the changes that food undergoes on digestion, assimilation, and use by the body. Physiological chemists can follow the greater part of the course of the wonderful and intricate changes which occur as the complex food substances are gradually broken down into simple chemical compounds, assimilated, and then built up into the various complex substances of the body. There is probably no part of science more fascinating than this consideration of the mechanism whereby inanimate food materials are converted into living flesh and blood. The simplest deseripton, unfortunately, must necessarily be highly technical, and would demand a considerable knowledge of chemistry on the part of the reader. It is, however, a matter of everyday experience, to take one simple case, that carbohydrates, such as*starch and sugar, on assimilation, are converted into fat in the body—a simple yet wonderful change still beyond the power of the chemist to reproduce in the laboratory.

For the present purpose it is fortunately necessary to consider only the final fate of the food, the form in which it is eliminated from the body. Carbohydrates and fats contain only the chemical elements carbon, hydrogen, and oxygen, and arc finally converted by the action of the oxygen absorbed through the lungs, into carbonic acid gas, and water, the products being exactly the same as those produced when carbohydrates and fats are burnt in a fire. The carbonic acid gas is eliminated in the breath, the water partly by the breath, party by surface evaporation, and partly by exertion. The amount of heat or energy produced by the combustion in the body, and this is the important fact, is the same as would be produced if the substances were ignited and burnt. It is consequently possible, by completely burning weighed quantities of foods in a calorimeter, to measure the amount of heat evolved, and so to arrive at their fuel or energy values when taken as food. These values are expressed as the number of heal units produced by the complete combustion of unit weight of material, and are the “iood values” about which so much has been written. In the case of proteins, which contain nitrogen, in addition to carbon, hydrogen, and oxygen, the changes in the body are not quite the same as those occurring on complete combustion, the nitrogen being mainly excreted as urea. Allowance has to be made for this fact, and for the small amount of protein not assimilated. Finally the results of the combustion experiments have been compared with those of elaborate experiments, in which men, under various conditions of feeding, rest and work, were enclosed in- large calorimeters for considerable periods, accurate observations being made of the food taken, the products evolved or excreted, the heat produced, and the work performed. Food values have thus been'fully verified.

Equal weights of carbohydrates and proteins have almost exactly the same fuel value. The fuel value of fats, however, is two and a quarter times that of proteins and carbohydrates. Thus the “food values” of olive oil or of purified lard, typical pure fats, is two and a-quarter times tliat of an equal weight of sugar, a pure carbohydrate. Nature in her wisdom and knowledge of fuel values provides a much greater amount of fat in the milk;of the reindeer of frigid climates than in that of the sheep and cow of temperate zones. Human milk and cows’ milk contain about 3.7 per cent, of fat, that of the sheep 0 per cent., while that of the reindeer contains 17 percent. The milk of the ass contains less than It per cent. The greaterfuel value of fat explains why the Eskimo and other inhabitants of polar regions require a diet composed largely of fat, in order tb maintain the body temperature, while fats are repulsive in large amount to inhabitants of tropical countries. From a knowledge of the percentages of proteins, carbohydrates, and fats in a food, combined with the fact that the fuel values of these constituents are respectively 4, 4 and fl calories, or heat units, per gram, it is easy to calculate Hie fuel value o_f the food. In most cases there is a large percentage of water present, which "does not contribute to the fuel value.

In the following paragraph are given the percentages of protein (P), carbohydrates (C), and fats

(F), and the heat units in calories (Cal.) per lb. of a number of typical foods as purchased: — Beef (average), P. 15.2, C. , F 15.5, Cal. 935; beef (best cuts), P. 16.4, C. —, F. 16.9, Cal. 1020; Beef (shank), P. 11.4, C. ,F. 4.5, Cal. 405; mutton (average), P. 13.8, C. —, F. 17.1, Cal. 977; pork, P. 12.0, C. —, F. 29.8, Cal. 1477; bacon, P. 9.5, C. —, F. 59.4, Cal. 2685; duck, P. 15.4, C. —, F. 16.0, Cal. 1085; fowl, P. 16.3, C. —, F. 10.2; rabbit, P. 21.5, C. —, F. 2.5, Cal. 504; fish (average, P. 10.9, C. —, F. 2.4, Cal. 295; Fish (fat), P. 20.0, C. —, F. 10.0, Cal. 770; Lard, P. 2.2, C. —, F. 94.0;' suet, P. 4.7, C. —, F. 81.8, Cal. 3540; eggs, P. 11.9, C. —, F. 9.3, Cal. 613; butter, P. 1.0, C. —, F. 83.0, Cal. 3510; Milk, P. 3.3, C. 5.0, F. 4.0, Cal. 322; cheese, P. 25.2, C. 2.4, F. 33.7, Cal. 1950; flour, P. 11.4, C. 74.8, F. 1.0, Cal. 1650; bread, P. 9.2, C. 53.1, F. 1.3, Cal. 1215; oatmeal, P. 14.2, C. 65.9, F. 7.3, Cal. 1795; rice, P. 7.4, C. 79.2, F. 0.4, Cal. 1620; sugar, P. __ c. 100.0,'F. —, Cal. 1790; potatoes, P. 2.2, C. 18.4, F. 0.1, 385; carrots, P. 1.1, C. 8.2, F. 0.4, Cal. 190; cabbage, P. 1.8, C. 5.8, F. 0.4, Cal. 165. In order to obtain the same fuel .value we should have to consume widely different amounts of different foods. Thus, to take a few examples, the following portions are all equivalent, each representing 400 calories: —Boz. beef, 7 oz. mutton, 2-toz. bacon, 5 eggs, 1 pint milk, 2oz. butter, 3 oz. cheese, 3Joz. oatmeal, sjoz. bread,,. 4oz. rice, 21b. carrots, and 2Jib. cabbage. The cost of these equivalent quantities varies by several hundred per cent., the bread costing less than Id, oatmeal Id, rice lid, bacon 3d, butter 31d, mutton 4d, beef fid to Bd, and eggs 10d. Provided that due attention be. first paid to all other essentials of diet, considerable economy might be effected by selecting those foods which arc cheapest from the point of view of fuel value. Disastrous results, however, might easily follow* from the selection of foods primarily on food values, with neglect of consideration of other and more important body requirements. In .the matter of food and nourishment a little scientific knowledge is indeed a dangerous thing. In the absence of sound, scientific knowledge it is safer to rely on the empyrical knowledge gained by the experience of countless generations. We have, however, departed from the dietetic habits of dur ancestors to no small extent, and have so purified some of our foods that important and sometimes essential constituents have been largely ‘purified out of them. In the interest of the health of the nation we are thus compelled to consider food values, proteins, mineral constituents and vita mines.