Black bread 7 lb.
Meat 7 lb.
Kvass (beer) 7.7 quarts.
Sour cabbage 24-1/2 gills = 122-1/2 oz.
Barley 24-1/2 gills = 122-1/2 oz.
Salts 10-1/2 oz.
Horse-radish 28 grains.
Pepper 28 grains.
Vinegar 5-1/2 gills = 26-1/2 oz.
DIETETICS, the science of diet, i.e. the food and nutrition of man in
health and disease (see NUTRITION). This article deals mainly with that
part of the subject which has to do with the composition and nutritive
values of foods and their adaptation to the use of people in health. The
principal topics considered are: (1) Food and its functions; (2)
Metabolism of matter and energy; (3) Composition of food materials; (4)
Digestibility of food; (5) Fuel value of food; (6) Food consumption; (7)
Quantities of nutrients needed; (8) Hygienic economy of food; (9)
Pecuniary economy of food.
1. _Food and its Functions._--For practical purposes, food may be
defined as that which, when taken into the body, may be utilized for the
formation and repair of body tissue, and the production of energy. More
specifically, food meets the requirements of the body in several ways.
It is used for the formation of the tissues and fluids of the body, and
for the restoration of losses of substance due to bodily activity. The
potential energy of the food is converted into heat or muscular work or
other forms of energy. In being thus utilized, food protects body
substance or previously acquired nutritive material from consumption.
When the amount of food taken into the body is in excess of immediate
needs, the surplus may be stored for future consumption.
Ordinary food materials, such as meat, fish, eggs, vegetables, &c.,
consist of inedible materials, or _refuse_, e.g. bone of meat and fish,
shell of eggs, rind and seed of vegetables; and _edible material_, as
flesh of meat and fish, white and yolk of eggs, wheat flour, &c. The
edible material is by no means a simple substance, but consists of
_water_, and some or all of the compounds variously designated as food
stuffs, proximate principles, nutritive ingredients or nutrients, which
are classified as _protein_, _fats_, _carbohydrates_ and _mineral
matters_. These have various functions in the nourishment of the body.
The _refuse_ commonly contains compounds similar to those in the food
from which it is derived, but since it cannot be eaten, it is usually
considered as a non-nutrient. It is of importance chiefly in a
consideration of the pecuniary economy of food. _Water_ is also
considered as a non-nutrient, because although it is a constituent of
all the tissues and fluids of the body, the body may obtain the water it
needs from that drunk; hence, that contained in the food materials is of
no special significance as a nutrient.
_Mineral matters_, such as sulphates, chlorides, phosphates and
carbonates of sodium, potassium, calcium, &c., are found in different
combinations and quantities in most food materials. These are used by
the body in the formation of the various tissues, especially the
skeletal and protective tissues, in digestion, and in metabolic
processes within the body. They yield little or no energy, unless
perhaps the very small amount involved in their chemical transformation.
Protein[1] is a term used to designate the whole group of nitrogenous
compounds of food except the nitrogenous fats. It includes the
albuminoids, as albumin of egg-white, and of blood serum, myosin of meat
(muscle), casein of milk, globulin of blood and of egg yolk, fibrin of
blood, gluten of flour; the gelatinoids, as gelatin and allied
substances of connective tissue, collagen of tendon, ossein of bone and
the so-called extractives (e.g. creatin) of meats; and the amids (e.g.
asparagin) and allied compounds of vegetables and fruits.
The albuminoids and gelatinoids, classed together as proteids, are the
most important constituents of food, because they alone can supply the
nitrogenous material necessary for the formation of the body tissues.
For this purpose, the albuminoids are most valuable. Both groups of
compounds, however, supply the body with energy, and the gelatinoids in
being thus utilized protect the albuminoids from consumption for this
purpose. When their supply in the food is in excess of the needs of the
body, the surplus proteids may be converted into body fat and stored.
The so-called extractives, which are the principal constituents of meat
extract, beef tea and the like, act principally as stimulants and
appetizers. It has been believed that they serve neither to build tissue
nor to yield energy, but recent investigations[2] indicate that creatin
may be metabolized in the body.
The _fats_ of food include both the animal fats and the vegetable oils.
The _carbohydrates_ include such compounds as starches, sugars and the
fibre of plants or cellulose, though the latter has but little value as
food for man. The more important function of both these classes of
nutrients is to supply energy to the body to meet its requirements above
that which it may obtain from the proteids. It is not improbable that
the atoms of their molecules as well as those from the proteids are
built up into the protoplasmic substance of the tissues. In this sense,
these nutrients may be considered as being utilized also for the
formation of tissue; but they are rather the accessory ingredients,
whereas the proteids are the essential ingredients for this purpose. The
fats in the food in excess of the body requirements may be stored as
body fat, and the surplus carbohydrates may also be converted into fat
and stored.
To a certain extent, then, the nutrients of the food may substitute each
other. All may be incorporated into the protoplasmic structure of body
tissue, though only the proteids can supply the essential nitrogenous
ingredients; and apart from the portion of the proteid material that is
indispensable for this purpose, all the nutrients are used as a source
of energy. If the supply of energy in the food is not sufficient, the
body will use its own proteid and fat for this purpose. The gelatinoids,
fats and carbohydrates in being utilized for energy protect the body
proteids from consumption. The fat stored in the body from the excess of
food is a reserve of energy material, on which the body may draw when
the quantity of energy in the food is insufficient for its immediate
needs.
What compounds are especially concerned in intellectual activity is not
known. The belief that fish is especially rich in phosphorus and
valuable as a brain food has no foundation in observed fact.
2. _Metabolism of Matter and Energy._--The processes of nutrition thus
consist largely of the transformation of food into body material and the
conversion of the potential energy of both food and body material into
the kinetic energy of heat and muscular work and other forms of energy.
These various processes are generally designated by the term metabolism.
The metabolism of matter in the body is governed largely by the needs of
the body for energy. The science of nutrition, of which the present
subject forms a part, is based on the principle that the transformations
of matter and energy in the body occur in accordance with the laws of
the conservation of matter and of energy. That the body can neither
create nor destroy matter has long been universally accepted. It would
seem that the transformation of energy must likewise be governed by the
law of the conservation of energy; indeed there is every reason a priori
to believe that it must; but the experimental difficulties in the way of
absolute demonstration of the principle are considerable. For such
demonstration it is necessary to prove that the income and expenditure
of energy are equal. Apparatus and methods of inquiry devised in recent
years, however, afford means for a comparison of the amounts of both
matter and energy received and expended by the body, and from the
results obtained in a large amount of such research, it seems probable
that the law obtains in the living organism in general.
The first attempt at such demonstration was made by M. Rubner[3] in
1894, experimenting with dogs doing no external muscular work. The
income of energy (as heat) was computed, but the heat eliminated was
measured. In the average of eight experiments continuing forty-five
days, the two quantities agreed within 0.47%, thus demonstrating what it
was desired to prove--that the heat given off by the body came solely
from the oxidation of food within it. Results in accordance with these
were reported by Studenski[4] in 1897, and by Laulanie[5] in 1898.
The most extensive and complete data yet available on the subject have
been obtained by W. O. Atwater, F. G. Benedict and associates[6] in
experiments with men in the respiration calorimeter, in which a subject
may remain for several consecutive days and nights. These experiments
involve actual weighing and analyses of the food and drink, and of the
gaseous, liquid and solid excretory products; determinations of
potential energy (heat of oxidation) of the oxidizable material received
and given off by the body (including estimation of the energy of the
material gained or lost by the body); and measurements of the amounts of
energy expended as heat and as external muscular work. By October 1906
eighty-eight experiments with fifteen different subjects had been
completed. The separate experiments continued from two to thirteen days,
making a total of over 270 days.