Human Foods and Their Nutritive Value by Harry Snyder (dark academia books to read .TXT) π
CHAPTER XXI
LABORATORY PRACTICE 299
Object of Laboratory Practice; Laboratory Note-book and Suggestions for Laboratory Practice; List of Apparatus Used; Photograph of Apparatus Used; Directions for Weighing; Directions for Measuring; Use of Microscope; Water in Flour; Water in Butter; Ash in Flour; Nitric Acid Test for Nitrogenous Organic Matter; Acidity of Lemons; Influence of Heat on Potato Starch Grains; Influence of Yeast on Starch Grains; Mechanical Composition of Potatoes; Pectose from Apples; Lemon Extract; Vanilla Extract; Testing Olive Oil for Cotton Seed Oil; Testing for Coal Tar Dyes; Determining the Per Cent of Skin in Beans; Extraction of Fat from Peanuts; Microscopic Examination of Milk; Formaldehyde in Cream or Milk; Gelatine in Cream or Milk; Testing for Oleomargarine; Testing for Watering or Skimming of Milk; Boric Acid in Meat; Microscopic Examination of Cereal Starch Grains; Identification
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246. Dietary Standards.βAs a result of a large number of dietary studies and digestion experiments, dietary standards have been prepared. Atwater in this country and Voit in Germany have proposed such standards for men employed at different kinds of labor, as follows:
drates Fuel
Value Nutritive lb. lb. lb. Calories Ratio Man with little physical exercise 0.20 0.20 0.66 2450 5.5 Man with light muscular work 0.22 0.22 0.77 2800 5.7 Man with moderate muscular work 0.28 0.28 0.99 3520 5.8 Man with active muscular work 0.33 0.33 1.10 4060 5.6 Man with hard muscular work 0.39 0.55 1.43 5700 6.9
In the table it will be seen that the quantity of nutrients increases with the labor to be performed. In order to secure the necessary heat and energy, rations for men at heavy labor contain proportionally more fat and carbohydrates than are required for light work. All dietary standards, however, should be regarded as tentative only. Opinions differ greatly on different points; for example, as to the amount of protein a ration should contain. This is a matter that can be determined only from extended investigations under a variety of conditions, and as yet results are too meager to formulate other than tentative standards. Chittenden has found that the body can be sustained on very much less protein than is called for in the standard ration.[77] The amount of protein in the ration should be ample to sustain the body weight and maintain a nitrogen equilibrium; that is, the income and outgo of nitrogen from the body should be practically equal.
but has been placed for information.
Fig. 58.βDietaries and Dietary Standards. (From Office of Experiment Stations Bulletin.)
"While one freely admits that health and a large measure of muscular strength may be maintained upon a minimum supply of protein, yet I think that a dispassionate survey of mankind will show that races which adopt such a diet are lacking in what, for want of a better word, one can only describe as energy." [28]
On the other hand, excessive and unnecessarily large amounts of protein are sometimes consumed, adding greatly to the cost of the ration and necessitating additional labor on the part of the body for its elimination.
247. Number of Meals per Day.βSome persons advocate two meals per day rather than three, but dietary studies show that the best results are secured when the food is divided among three rather than two meals, and with a two-meal system the tendency is to consume a larger total amount of food than when three meals are eaten. It is not essential that the food be equally divided among the three meals. Any one of them may be lighter or more substantial as the habits and inclinations of the individual dictate. If it is found necessary to reduce the total quantity of food consumed, this may be done by a proportional reduction of each of the meals, or of any one of them instead of decreasing the number of meals per day. The occasional missing of a meal is sometimes beneficial, in cases of digestion disorders, but the ordinary requirements of persons in normal health who have either mental or physical labor to perform are best met when three meals per day are consumed, as this insures an even supply of nutrients. For persons of sedentary habits, the kind and quantity of food at each meal must be regulated largely by the individual from knowledge based on personal experience.
"In the matter of diet every man must, in the last resort, be a law unto himself; but he should draw up his dietetic code intelligently and apply it honestly, giving due heed to the warnings which nature is sure to address to him should he at any time transgress."[28]
If there is trouble in digesting the food, it is well to study the other habits of life along with the food question, for it may be the difficulty arises from some other cause, and would be remedied by more exercise and fresh air, avoiding rush immediately after meals, more thorough mastication, or less worry. It is a serious matter to shut off the supply of food from a person not suffering from some disease and who is working; as well cut off the supply of fuel from a furnace and then expect a full amount of energy and heat. But unlike the furnace, when the human body is deprived of needed nutrients it preys upon itself and uses up its reserve that should be drawn upon only in cases of illness or extreme nervous strain. Some persons live in such a way as to never have any reserve of strength and energy to call upon but use up each day all the body can produce and so become physical bankrupts when they should be in their prime. Food is required for the production of nerve energy as well as physical energy.[78]
248. Mixed Dietary Desirable.βExperiments in the feeding of farm animals show that the best results come from the combination of a number of foods to form a mixed ration, rather than from the use of one food alone,[79] for in this way the work of digestion is more evenly distributed, and a higher degree of efficiency is secured from the foods consumed. The same is true in human feeding; the best results are secured from a mixed diet. Ordinarily, about two fifths of the nutrients of a ration are derived from animal and three fifths from vegetable sources.
249. Animal and Vegetable Foods; Economy of Production.βAnimal foods can never compete in cheapness of the nutrients with cereals and vegetables, as it takes six to eight pounds or more of a cereal, together with forage crops, to make a pound of meat. Hence the returns in food value are very much larger from the direct use of the cereals as human food, than from the feeding of cereals to cattle and the use of the meat. As the population of a country increases, and foods necessarily become more expensive, cereals are destined to replace animal foods to a great extent, solely as a matter of economy.
250. Food Habits.βLong-established dietary habits and customs are not easily changed, and when the body becomes accustomed to certain foods, substitution of others, although equally valuable, may fail to give satisfactory results. For example, immigrants from southern Europe demand foods with which they are familiar, as macaroni, olive oil, and certain kinds of cheese, foods which are generally imported and more expensive than the staples produced in this country,[80] and when they are compelled to live on other foods, even though they have as many nutrients, they complain of being underfed. Previously acquired food habits appear to affect materially the process of digestion and assimilation. Sudden and pronounced change in the feeding of farm animals is attended with unsatisfactory results, and whenever changes are made in the food of either humans or animals they should be gradual rather than radical.
251. Underfed Families.βAs the purchasing of food is often done by inexperienced persons, palatability rather than nutritive value is made the basis of choice. Dietary studies show that because of lack of knowledge of the nutritive value of foods, whole families are often underfed. Particularly is this true where the means for purchasing foods are limited. In dietary studies among poor families in New York City,[81] the United States Department of Agriculture notes: "It is quite evident that what is needed among these families more than anything else is instruction in the way to make the little they have go the farthest." Some classes of the rich too are equally liable to be underfed, as they are more prone to food notions and are able to indulge them. Among the children of the rich are found some as poorly nourished as among the poor.
252. Cheap and Expensive Foods.βAmong the more expensive items of a ration are meats, butter, and canned fruits. The difference in composition and nutritive value between various cuts of meat is small, being largely physical, and affecting taste and flavor rather than nutritive value. Expensive cuts of meat, high-priced breakfast cereals, tropical fruits and foods which impart special flavors, add little in the way of nutritive value to the ration, but greatly enhance the cost of living. Ordinarily the cheapest foods are corn meal, wheat flour and bread, milk, beans, cheese, sugar, and potatoes.[7] The amount of animal and vegetable foods to combine with these to form a balanced ration may be governed largely by personal preference or cost, as there is little difference in nutritive value. The selection of foods on the basis of cost and nutritive value is discussed in Chapter XVI.
253. Food Notions.βMany erroneous ideas exist as to the nutritive value of foods, and often wholesome and valuable foods are discriminated against because of prejudice. Skim milk is usually regarded as containing little if any nourishing material, when in reality it has a high protein content, and can be added to other foods to increase their nutritive value. The less expensive cuts of meat contain more total nutrients than many of the more expensive ones. Beef extracts have been erroneously said to contain more nutrients than beef,[51] and mushrooms to be equal in value of beefsteak; chemical analyses fail to confirm either statement. The banana also has been overestimated as to food value, and while it contains more nutrients than many fruits, it is not the equal of cereals, as has been claimed.[82] Cocoa, although a valuable beverage, adds but little in the way of nutrients to a ration unless it is made with milk. The value of a food should be based upon its composition as determined by chemical analysis, its digestibility as founded upon digestion experiments, and its palatability and mechanical structure. Food notions have, in
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