_Laboratory exercise._--Composition of common foods. The
series of food charts supplied by the United States
Department of Agriculture makes an excellent basis for a
laboratory exercise to determine common foods rich in (_a_)
water, (_b_) starch, (_c_) sugar, (_d_) fats or oils, (_e_)
protein, (_f_) salts, (_g_) refuse.
_Demonstration._--Method of using bomb calorimeter.
_Laboratory and home exercise._--To determine the best
individual balanced dietary (using standard of Atwater,
Chittenden, or Voit) as determined by the use of the
100-Calorie portion.
_Demonstration._--Tests for some common adulterants.
_Demonstration._--Effect of alcohol on protein, _e.g._ white
of egg.
_Demonstration._--Alcohol in some patent medicines.
_Demonstration._--Patent medicines containing acetanilid.
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 deg. 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:--