WATER, SALTS, COOKING, ETC.
Water does not afford energy since it is already completely "burnt" or oxidized. It may be looked on, however, as a kind of food as it is necessary for the proper working of the animal machine; it can be compared to some extent to the lubricating oil used for the moving parts of the petrol motor. Water is continually being lost in the urine and lungs and sweat and faeces and it must be replaced. The mineral constituents of the human body amount to 4.3-4.4%. The only salt commonly consumed as such is table salt or sodium chloride (NaC1). The various salts needed by the body are present in small amounts in food, particularly in milk and in vegetables. 1-2 g. of NaC1 are needed daily, and while custom varies con siderably, the average intake is probably nearer 8–io g. Possibly habit has resulted in the use of much more NaCl in the human dietary than is physiologically necessary. 0.9-1 g. of calcium is needed daily (Sherman), and the minimum necessary for the maintenance of a calcium balance is 0.63 g. calcium per 7o kg. of body weight. Of the American diets investigated by Sherman 15% were found to be deficient in calcium. A sufficient calcium supply is very important, especially in children because calcium phosphate is the chief constituent of bone and is best obtained by the ingestion of liberal quantities of milk. Of phosphate o.88 g. is the minimum needed per 7o kg. body weight, but there is no risk of phosphorus shortage in diets yielding 3,00o C. daily unless large amounts of degerminated patent flour are consumed as the principal cereal.
Iron is an essential constituent of the food since it is its pres ence in the haemoglobin of the red corpuscles which endows the blood with the power of transporting oxygen from the lungs to the tissues. The daily intake of iron should be not less than 12 mgm. daily, a figure which should be increased in pregnancy and in lactation. It must be mentioned that milk is very deficient in iron, and that this substance is principally obtained from animal food and the chlorophyll of green vegetables. It has been shown in animal experiments that iron deficiency leads to impoverish ment of the blood and stunting of growth. A similar anaemia develops in infants at the 6th month if they have been fed ex clusively on milk, but rapid recovery is noted when a mixed diet is commenced. It is now advised that infants shall be given small amounts of soups prepared from marrow bones and mixed vege tables from the 3rd month onwards, partly to prevent this anaemia.
Iodine in minute traces is essential for the preparation of thyroxin which is the name given to the active principle of the secretion of the thyroid gland. In districts in which the iodine supplies in the drinking water are insufficient simple goitre fre quently develops. This may be prevented or the condition may be cured by the use of iodized table salt, or by the deliberate addition of iodine to the water supply (see GOITRE).
The real objection to the free use of meat (see VEGETARIANISM) is that though animals are partly fed on materials not required for human consumption (cow, sheep), they are to some extent grain fed (pig, fowl), or live on products that are grown on land which might otherwise be used for vege tables, grain or fruit. To this extent animals compete with man for utilizable foods. The cow, pig and fowl consume 12-14 lb. dry fodder for each lb. of dry human food produced (as meat; eggs, etc.) ; the sheep 24 lb. and the ox 64 lb. (Wood). Prime beef is thus the most extravagant of all forms of animal food as regards the quantity of vegetable food required to produce it. Because of these facts, meat is dear, and if too large a propor tion of the income is expended on meat there is not enough left for milk and vegetables which are indispensable constituents of the diet.
The great disadvantage of a purely vegetarian diet is its bulk. This objection does not apply to a lacto-vegetarian diet which permits the free, use of milk and eggs; in fact such a diet has much to commend it (Greenwald). It need not be bulky. The milk and eggs furnish protein of exceptionally good quality to compensate for possible deficiencies in those supplied by other articles of the diet, and they contain much phosphorus and cal cium, the latter of which is apt to be present in inadequate amounts if milk is not included in the diet and they furnish a con siderable, if seasonally-varying quantity of some of the vitamins. Moreover the cow and hen return in the form of milk and eggs much more of the energy they receive than they do if kept for their meat (Armsby).
The great value of cooking lies in making dishes attractive to the palate and other senses and thus ensuring an adequate intake of food; it improves the digestibility of certain classes of food partly by splitting the envelopes of the starchy granules and also by destroying certain substances which prevent the action of the digestive enzymes. It kills micro-organisms and other parasites. It has a destructive action, however, on some of the vitamins, but this is of considerable extent only in the case of the antiscorbutic factor, and it can be readily compensated for by taking fresh fruit or vegetables.
When the diet is controlled by authority the essential points to be bome in mind are :—the provision of the necessary calories, which will almost certainly ensure adequate amounts of protein; the maintenance of a minimum fat supply; plentiful supplies of milk and milk products especially for children and of fresh vegetable food.
To illustrate how the prac tical problems of dietetics are treated, a brief reference will be made to the procedure in the navy and army.
In the British navy (see Appendix XIX. King's Regulations and Admiralty Instructions) the daily standard ration, service afloat, is io oz. bread, 1 lb. fresh meat, lb. fresh vegetables or 4 oz. haricot beans or marrow fat beans when fresh vegetables are not available, 1 pint spirit, 2 oz. sugar, oz. tea, 1 oz. choco late (or oz. coffee), oz. condensed milk, oz. jam, marma lade or pickles, 4 oz. corned beef on one day of the week in har bour or on two days at sea, mustard, pepper, vinegar and salt as required. This ration is supplemented by money allowances, out of which the men purchase at their discretion the extra foodstuffs necessary to complete their messing.
In the army (see 4o/W0/8263 [Management of Soldiers Messing] and 4o/W0/9071 [Manual of Military Cooking and Dietary]) the diet provided contains Protein 136 g., Fats 138 g., Carbohydrates 442 g.
The daily scale of rations is :—Meat, fresh or frozen 12 oz. (or preserved meat 9 oz.) ; bread 16 oz. (or biscuits 12 OZ.) bacon 2 oz.; sugar oz.; tea oz.; suet oz.; cheese oz.; jam or syrup oz.; margarine oz. Messing cash allowance of 31 d. per day.
Schaefer, Text Book of Physiology, vol. 1, p. 868 Bibliography.—Schaefer, Text Book of Physiology, vol. 1, p. 868 (1898) ; Chittenden, Nutrition of Man (i9o7)*; Hindhede, Protein and Nutrition (1913)*; Royal Society Committee, Food Supply of United Kingdom (1917) Lusk, Science of Nutrition (i9I9)*; Star ling, Feeding of Nations (i9i9)*; Benedict, Metabolism and growth from birth to puberty, Carnegie Instit. Publications No. 302 (1921)*; Greenwald, "Normal Diet" in Barker's Endocrinology and Metabolism (1922)*; various authors, "Dietary constituents and their derivatives" Ibid. pp. 81--356*; Kellogg, New Dietetics (1923)*. (Those marked * have bibliographies.) Sherman, Chemistry of Food and Nutrition and Food Products; McCollum, Newer Knowledge of Nutrition; McLester, Nutrition and Diet in Health and Disease; Foundations of Nutrition; Feeding the Family. (S. WR.)
