Determination of acetanilid.
Why we Need Food.--A locomotive engine takes coal, water, oxygen, from its environment. A living plant or animal takes organic food, water, and oxygen from its environment. Both the living and nonliving machine do the same thing with this fuel or food. They oxidize it and release the energy in it.
But the living organism in addition may use the food to repair parts that have broken down or even build new parts. _Thus food may be defined as something that releases energy or that forms material for the growth or repair of the body of a plant or animal._ The millions of cells of which the body is composed must be given material which will form more living matter or material which can be oxidized to release energy when muscle cells move, or gland cells secrete, or brain cells think.
[Illustration: The composition of milk. Why is it considered a good food?]
Nutrients.--Certain nutrient materials form the basis of food of both plants and animals. These have been stated to be _proteins_ (such as lean meat, eggs, the gluten of bread), _carbohydrates_ (starches, sugars, gums, etc.), _fats_ and _oils_ (both animal and vegetable), _mineral matter_ and _water_.
Proteins.--Protein substances contain the element nitrogen. Hence such foods are called nitrogenous foods. Man must form the protoplasm of his body (that is, the muscles, tendons, nervous system, blood corpuscles, the living parts of the bone and the skin, etc.) in part at least from nitrogenous food. Some of this he obtains by eating the flesh of animals, and some he obtains directly from plants (for example, peas and beans).
Proteins are the only foods available for tissue building. They may be oxidized to release energy if occasion requires it.
Fats and Oils.--Fats and oils, both animal and vegetable, are the materials from which the body derives part of its energy. The chemical formula of a fat shows that, compared with other food substances, there is very little oxygen present; hence the greater capacity of this substance for uniting with oxygen. The rapid burning of fat compared with the slower combustion of a piece of meat or a piece of bread illustrates this. A pound of butter releases over twice as much energy to the body as does a pound of sugar or a pound of steak. Human fatty tissue is formed in part from fat eaten, but carbohydrate or even protein food may be changed and stored in the body as fat.
Carbohydrates.--We see that the carbohydrates, like the fats, contain carbon, hydrogen, and oxygen. _Carbohydrates are essentially energy-producing foods._ They are, however, of use in building up or repairing tissue. It is certainly true that in both plants and animals such foods pass directly, together with foods containing nitrogen, to repair waste in tissues, thus giving the needed proportion of carbon, oxygen, and hydrogen to unite with the nitrogen in forming the protoplasm of the body.
[Illustration: Three portions of foods, each of which furnishes about the same amount of nourishment.]
Inorganic Foods.--Water forms a large part of almost every food substance.
It forms about five sixths of a normal daily diet. The human body, by weight, is about two thirds water. About 90 per cent of the blood is water.
Water is absolutely essential in passing off waste of the body. When we drink water, we take with it some of the inorganic salts used by the body in the making of bone and in the formation of protoplasm. Sodium chloride (table salt), an important part of the blood, is taken in as a flavoring upon our meats and vegetables. Phosphate of lime and potash are important factors in the formation of bone.
Phosphorus is a necessary substance for the making of living matter, milk, eggs, meat, whole wheat, and dried peas and beans containing small amounts of it. Iron also is an extremely important mineral, for it is used in the building of red blood cells. Meats, eggs, peas and beans, spinach, and prunes, are foods containing some iron.
Some other salts, compounds of calcium, magnesium, potassium, and phosphorus, have been recently found to aid the body in many of its most important functions. The beating of the heart, the contraction of muscles, and the ability of the nerves to do their work appear to be due to the presence of minute quantities of these salts in the body.
Uses of Nutrients.--The following table sums up the uses of nutrients to man:[36]--
Protein Forms tissue White of eggs (albumen), (muscles, tendon, } curd of milk (casein), lean and probably } All serve as meat, gluten of wheat, etc. fat) } _fuel_ and yield } _energy_ in form Fats Form fatty tissue. } of heat and muscular Fat of meat, butter, olive oil, } strength.
oils of corn and wheat, etc. } } Carbohydrates Transformed into } Sugar, starch, etc. fat. /
Mineral matters (ash) Aid in forming bone, Phosphates of lime, potash, assist in digestion, soda, etc. aid in absorption and in other ways help the body parts do their work.
Water used as a vehicle to carry nutrients, and enters into the composition of living matter.
Footnote 36: Adapted from Atwater, _Principles of Nutrition and Nutritive Value of Food_, U. S. Department of Agriculture, 1902.
Common Foods contain the Nutrients.--We have already found in our plant study that various plant foods are rich in different nutrients, carbohydrates forming the chief nutrient in the foods we call cereals, breads, cake, fleshy fruits, sugars, jellies, and the like. Fats and oils are most largely found in nuts and some grains. Animal foods are our chief supply of protein. White of egg and lean meat are almost pure protein and water. Proteins are most abundant, as we should expect, in those plants which are richly supplied with nitrogen; peas and beans, and in grains and nuts. Fats, which are melted into oils at the temperature of the body, are represented by the fat in meats, bacon, pork, lard, butter, and vegetable oils.
Water.--Water is, as we have seen, a valuable part of food. It makes up a very high percentage of fresh fruits and vegetables; it is also present in milk and eggs, less abundant in meats and fish, and is lowest in dried foods and nuts. The amount of water in a given food is often a decided factor in the cost of the given food, as can easily be seen by reference to the chart on page 283.
Refuse.--Some foods bought in the market may contain a certain unusable portion. This we call refuse. Examples of refuse are bones in meat, shells of eggs or of shellfish, the covering of plant cells which form the skins of potatoes or other vegetables. The amount of refuse present also plays an important part in the values of foods for the table. The table[37] on page 276 gives the percentages of organic nutrients, water, and refuse present in some common foods.
[Illustration: Table of food values. Determine the percentage of water in codfish, loin of beef, milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and potatoes. What _is_ the refuse in each case?
Find three foods containing a high percentage of protein; of fat; of carbohydrate. Find some food in which the proportions of protein, fat, and carbohydrate are combined in a good proportion.]
Fuel Values of Nutrients.--In experiments performed by Professor Atwater and others, and in the appended tables, the value of food as a source of energy is stated in heat units called _Calories_. _A Calorie is the amount of heat required to raise the temperature of one kilogram of water from zero to one degree Centigrade._ This is about equivalent to raising one pound four degrees Fahrenheit. The fuel value of different foods may be computed in a definite manner. This is done by burning a given portion of a food (say one gram) in the apparatus known as a _calorimeter_. By this means may be determined the number of degrees the temperature of a given amount of water is raised during the process of burning. It has thus been found that a gram of fat will liberate 9.3 Calories of heat, while a gram of starch or sugar only about 4 Calories. The burning value of fat is, therefore, over twice that of carbohydrates. In a similar manner protein has been shown to have about the same fuel value as carbohydrates, _i.e._ 4 Calories to a gram.[38]
Footnote 37 and 38: W. O. Atwater, _Principles of Nutrition and Nutritive Value of Food_, U. S. Department of Agriculture, 1902.
The Relation of Work to Diet.--It has been shown experimentally that a man doing hard, muscular work needs more food than a person doing light work.
The mere exercise gives the individual a hearty appetite; he eats more and needs more of all kinds of food than a man or boy doing light work.
Especially is it true that the person of sedentary habits, who does brain work, should be careful to eat less food and food that will digest easily.
His protein food should also be reduced. Rich or hearty foods may be left for the man who is doing hard manual labor out of doors, for any extra work put on the digestive organs takes away just so much from the ability of the brain to do its work.
[Illustration: Foods of plant origin. Select 5 foods containing a high percentage of protein, 5 with a high percentage of carbohydrates, 5 with a high percentage of water. Do vegetable foods contain much fat? Which of the above-mentioned foods have the highest burning value?]
[Illustration: Foods largely of animal origin. Compare with the previous chart with reference to amount of protein, carbohydrate, and fat in foods.
Compare the burning value of plant and animal foods. Compare the relative percentage of water in both kinds of foods.]
[Illustration: The composition of milk.]
The Relation of Environment to Diet.--We are all aware of the fact that the body seems to crave more food in winter than in summer. The temperature of the body is maintained at 98.6 in winter as in summer, but much more heat is lost from the body in cold weather. Hence feeding in winter should be for the purpose of maintaining our fuel supply. We need heat-producing food, and we need _more_ food in winter than in summer. We may use carbohydrates for this purpose, as they are economical and digestible. The inhabitants of cold countries get their heat-releasing foods largely from fats. In tropical countries and in hot weather little protein should be eaten and a considerable amount of fresh fruit used.
The Relation of Age to Diet.--As we will see a little later, age is a factor not only in determining the kind but the amount of food to be used.
Young children require far less food than do those of older growth or adults. The body constantly increases in weight until young manhood, or womanhood, then its weight remains nearly stationary, varying with health or illness. It is evident that food in adults simply repairs the waste of cells and is used to supply energy. Elderly people need much less protein than do younger persons. But inasmuch as the amount of food to be taken into the body should be in proportion to the body weight, it is also evident that growing children do not, as is popularly supposed, need as much food as grown-ups.
The Relation of Sex to Diet.--As a rule boys need more food than girls, and men than women. This seems to be due to, first, the more active muscular life of the man and, secondly, to the greater amount of fat in the tissues of the woman, making loss of heat less. Larger bodies, because of greater surface, give off more heat than smaller ones. Men are usually larger in bulk than are women,--another reason for more food in their case.
The Relation of Digestibility to Diet.--Animal foods in general may be said to be more completely digested within the body than plant foods. This is largely due to the fact that plant cells have woody walls that the digestive juices cannot act upon. Cereals and legumes are less digestible foods than are dairy products, meat, or fish. This does not mean necessarily that these foods would not agree with you or me but that in general the body would get less nourishment out of the total amount available.
The agreement or disagreement of food with an individual is largely a personal matter. I, for example, cannot eat raw tomatoes without suffering from indigestion, while some one else can digest tomatoes but not strawberries. Each individual should learn early in life the foods that disagree with him personally and leave such foods out of his dietary. For "what is one man's meat may be another man's poison."
The Relation of Cost of Food to Diet.--It is a mistaken notion that the best foods are always the most expensive. A glance at the table (page 283) will show us that both fuel value and tissue-building value is present in some foods from vegetable sources, as well as in those from animal sources, and that the vegetable foods are much cheaper. The American people are far less economical in their purchase of food than most other nations. Nearly one half of the total income of the average workingman is spent on food.
Not only does he spend a large amount on food, but he wastes money in purchasing the wrong kinds of food. A comparison of the daily diets of persons in various occupations in this and other countries shows that as a rule we eat more than is necessary to supply the necessary fuel and repair, and that our workingmen eat more than those of other countries. Another waste of money by the American is in the false notion that a large proportion of the daily dietary should be meat. Many people think that the most expensive cuts of meat are the most nutritious. The falsity of this idea may be seen by a careful study of the tables on pages 283 and 286.
The Best Dietary.--Inasmuch as all living substance contains nitrogen, it is evident that protein food must form a part of the dietary; but protein alone is not usable. If more protein is eaten than the body requires, then immediately the liver and kidneys have to work overtime to get rid of the excess of protein which forms a poisonous waste harmful to the body. We must take foods that will give us, as nearly as possible, the proportion of the different chemical elements as they are contained in protoplasm. It has been found, as a result of studies of Atwater and others, that a man who does muscular work requires a little less than one quarter of a pound of protein, the same amount of fat, and about one pound of carbohydrate to provide for the growth, waste, and repair of the body and the energy used up in one day.
The Daily Calorie Requirement.--Put in another way, Atwater's standard for a man at light exercise is food enough to yield 2816 Calories; of these, 410 Calories are from protein, 930 Calories from fat, and 1476 Calories from carbohydrate. That is, for every 100 Calories furnished by the food, 14 are from protein, 32 from fat, and 54 from carbohydrate. In exact numbers, the day's ration as advocated by Atwater would contain about 100 grams or 3.7 ounces protein, 100 grams or 3.7 ounces fat, and 360 grams or 13 ounces carbohydrate. Professor Chittenden of Yale University, another food expert, thinks we need proteins, fats, and carbohydrates in about the proportion of 1 to 3 to 6, thus differing from Atwater in giving less protein in proportion. Chittenden's standard for the same man is food to yield a total of 2360 Calories, of which protein furnishes 236 Calories, fat 708 Calories, and carbohydrates 1416 Calories. For every 100 Calories furnished by the food, 10 are from protein, 30 from fat, 60 from carbohydrate. In actual amount the Chittenden diet would contain 2.16 ounces protein, 2.83 ounces fat, and 13 ounces carbohydrate. A German named Voit gives as ideal 25 Calories from proteins, 20 from fat, and 55 from carbohydrate, out of every 100 Calories; this is nearer our actual daily ration. In addition, an ounce of salt and nearly one hundred ounces of water are used in a day.
[Illustration: Table showing the cost of various foods. Using this table, make up an economical dietary for one day, three meals, for a man doing moderate work. Give reasons for the amount of food used and for your choice of foods. Make up another dietary in the same manner, using expensive foods. What is the difference in your bill for the day?]
A Mixed Diet Best.--Knowing the proportion of the different food substances required by man, it will be an easy matter to determine from the tables and charts shown you the best foods for use in a mixed diet. Meats contain too much nitrogen in proportion to the other substances. In milk, the proportion of proteins, carbohydrates, and fats is nearly right to make protoplasm; a considerable amount of mineral matter being also present. For these reasons, milk is extensively used as a food for children, as it combines food material for the forming of protoplasm with mineral matter for the building of bone. Some vegetables (for example, peas and beans) contain a large amount of nitrogenous material but in a less digestible form than is found in some other foods. Vegetarians, then, are correct in theory when they state that a diet of vegetables may contain everything necessary to sustain life. But a mixed diet containing meat is healthier. A purely vegetable diet contains much waste material, such as the cellulose forming the walls of plant cells, which is indigestible. It has been recently discovered that the outer coats of some grains, as rice, contain certain substances (enzymes) which aid in digestion. In the case of polished rice, when this outer coat is removed the grain has much less food value.
Daily Fuel Needs of the Body.--It has been pointed out that the daily diet should differ widely according to age, occupation, time of year, etc. The following table shows the daily fuel needs for several ages and occupations:--
DAILY CALORIE NEEDS (APPROXIMATELY)
1. For child under 2 years 900 Calories 2. For child from 2-5 years 1200 Calories 3. For child from 6-9 years 1500 Calories 4. For child from 10-12 years 1800 Calories 5. For child from 12-14 (woman, light work, also) 2100 Calories 6. For boy (12-14), girl (15-16), man, sedentary 2400 Calories 7. For boy (15-16) (man, light muscular work) 2700 Calories 8. For man, moderately active muscular work 3000 Calories 9. For farmer (busy season) 3200 to 4000 Calories 10. For ditchers, excavators, etc. 4000 to 5000 Calories 11. For lumbermen, etc. 5000 and more Calories
Normal Heat Output.--The following table gives the result of some experiments made to determine the hourly and daily expenditure of energy of the average normal grown person when asleep and awake, at work or at rest:--
AVERAGE NORMAL OUTPUT OF HEAT FROM THE BODY ========================================================== AVERAGE CONDITIONS OF MUSCULAR ACTIVITY CALORIES PER HOUR -------------------------------------------+-------------- Man at rest, sleeping 65 Calories Man at rest, awake, sitting up 100 Calories Man at light muscular exercise 170 Calories Man at moderately active muscular exercise 290 Calories Man at severe muscular exercise 450 Calories Man at very severe muscular exercise 600 Calories ==========================================================
It is very simple to use such a table in calculating the number of Calories which are spent in twenty-four hours under different bodily conditions. For example, suppose the case of a clerk or school teacher leading a relatively inactive life, who
sleeps for 9 hours 65 Calories = 585 works at desk 9 hours 100 Calories = 900 reads, writes, or studies 4 hours 100 Calories = 400 walks or does light exercise 2 hours 170 Calories = 340 ---- 2225
This comes out, as we see, very close to example 6 of the table[39] on page 284.