DIET.
The importance of a duly proportioned and sufficient dietary is shown
by its great influence on health and constitution. An ill-proportioned
or deficient diet is certain to lead to failure of health. The anatomy
of an animal may be modified in the course of generations by altered
diet, as well as its character; thus, the alimentary canal of the cat
has increased in length to adapt it to its omnivorous habits. In the
case of the bee we have a still more remarkable instance. If by any
accident the queen bee dies, or is lost, the working bees (which are
sexually undeveloped) select two or three eggs, which they hatch in
large cells, and then feed the maggot on a stimulating jelly, different
from that supplied to the other maggots, thus producing a queen bee.
The food of mankind varies naturally with—
I.—_Climate._ A cold climate leads to increased metabolism, and
consequently a large amount of fatty matter can be eaten without
producing nausea. Witness the difference between a Laplander’s and a
Hindoo’s diet.
The _season_ of the year has likewise some influence. Vital processes
are more active in spring than autumn, and more food is consequently
required in the former season.
II.—_Occupation._ Although muscular exercise is not associated with
an immediate increase of elimination of urea, yet as a matter of
experience more nitrogenous food is required and can be metabolised
by hard workers than by idlers. The trappers on the North American
prairies can live for weeks together on meat alone, accompanied
by copious draughts of tea. They are constantly in the open air,
undergoing fatiguing exercises, in a dry and rare atmosphere. For
brain workers no special food is required. Foods containing phosphorus
have no special value, so far as is known, for mental work. Such work,
however, is apt to affect digestion; consequently the digestibility of
food is more important for those engaged in sedentary occupations than
its chemical composition.
III.—_Sex._ As a rule, women require about one-tenth less food than
men, but probably this rule hardly holds good in the case of women
engaged in laborious work.
IV.—_Age._ Infants require only milk, and the less they have of any
other food before a year old the better. Atwater has calculated that——
A child under 2 requires 3∕10 the food of a man doing moderate work.
„ of 3 to 5 „ 4∕10 „ „ „ „
„ of 6 to 9 „ 5∕10 „ „ „ „
„ of 10 to 13 „ 6∕10 „ „ „ „
A girl of 14 to 16 „ 7∕10 „ „ „ „
A boy of 14 to 16 „ 8∕10 „ „ „ „
Vital processes are more active in early life, and food is required
not only to carry on the functions of the body, but also to furnish
the materials for growth. Hence, while the proportion of proteids to
carbohydrates and fats should be—
As 1:5.3 in adults, it should be about as 1:4.3 in children.
After the age of thirty-five or forty, the tendency is to take too much
food. All the tissues of the body are established, and excess of food
(especially nitrogenous food) is liable to produce tissue degeneration
by loading the system with partially metabolised matter, and may lead
to gouty diseases. It is much safer to take what may be regarded as too
little than too much food after this period.
=Times for Eating.=—The best arrangement seems to be to have three
meals, each fairly nutritious, and containing all the constituents
required. The Romans only had two meals daily, prandium and cœna. This
is common among the French at present, but it tends to overloading the
digestive organs at these meals.
An ordinary full meal has usually passed from the stomach in four
hours. Fresh food ought never to be introduced before this period; it
is advisable to allow an interval of five hours between meals for the
healthy, so as to give time for the digestive organs to rest, and for
the absorption of food. The practice of taking tea with the chief meal,
or a “meat tea,” is bad. Tea is better taken an hour or two after food.
Regularity in the time of taking meals is important, as the digestive
organs acquire habits like other parts of the body. Work ought not, if
possible, to be resumed immediately after meals, nor active exercise of
any kind. These tend to abstract blood from the digestive organs, and
so diminish the efficiency of digestion.
=Vegetable and Animal Foods.=—The fact that the food we require can
be obtained from the vegetable world has led to the proposition that
vegetable food should be taken alone. It is urged in favour of this
plan, that a large amount of suffering to animals would be prevented.
Also that animal food is not so economical as vegetable, land being
more economically employed in producing corn than in feeding cattle.
Thirdly, there is the indubitable fact that health can be maintained
for prolonged periods on vegetable food (including nuts, cereals,
fruits, etc.)
On the other hand, the chief objections to a purely vegetable diet are
that the undigested refuse is greater than with an equal quantity of
animal food; that a longer time and more exertion than for animal foods
are required in digesting the most nutritious vegetable foods, such
as legumens, while other vegetable foods do not contain a sufficient
proportion of nitrogenous material. Also, if one lived entirely on
vegetable food, a greater bulk would be required, and owing to the fact
that such food is less easily absorbed, satisfaction to the appetite
would not so soon be produced. Animal food has a great advantage as
regards convenience. Man is not an eating machine; he requires food
which is easily converted into the body substance, and this is supplied
by the flesh of animals, milk and eggs, with a due proportion of
non-nitrogenous food; sheep and oxen work up indigestible vegetable
materials into easily assimilable mutton and beef. The greater
convenience of animal food as a supply of proteid is shown by the
following examples of foods _after the removal of water_:—
100 parts of rice contain 7 parts of proteid.
„ wheat „ 16 „ „
„ pea flour „ 27 „ „
„ fat beef „ 51 „ „
„ dried lean beef „ 89 „ „
On the other hand, vegetable foods are a cheaper source, not only
of carbohydrates and fats, but also of proteids as well. Thus the
approximate cost of—
1 lb. of proteid in beef is 2s. 8d.
„ „ milk is 2s. 2d.
„ „ bread is 1s. 6d.
„ „ oatmeal is 7½d.
„ „ peas is 7d.
Under the ordinary conditions of town life, there is considerable
danger of indulging in an excess of nitrogenous food, and vegetarians
may therefore do good by showing that meat is not absolutely necessary,
and can often with advantage be largely replaced by vegetable food.
If we include milk, cheese, and eggs in the vegetarian diet, the
objections to it partially disappear; and it would be well if it were
much more widely known, especially among the poor, that on these,
together with vegetables, health can be maintained with the addition of
little or no meat.
=The Determination of Diet.=—The first principle in making a dietary
is that it =must be mixed=, containing all the necessary constituents,
proteids, hydrocarbons, carbohydrates, water, and salts. No one
of these alone will support life for any considerable period.
Carbohydrates (sugar and starch) can be most easily dispensed with;
fats, on the other hand, are essential for the maintenance of health.
The next point is to ascertain =the proportion= in which these
different foods are required. _Salts_ are commonly taken with other
foods, common salt being the only one taken alone. The amount required
is given on p. 7. The amount of _water_ required varies with the
season of the year, the amount of exercise and perspiration, and other
factors. As a rule, not more than two pints of water are required per
day, and still less if fruit is freely taken. We may therefore confine
our attention to the carbonaceous and nitrogenous foods, and try to
ascertain the amount of each of these required. Every diet must be
subjected to the following tests, to fully ascertain its value:—
1. =The Chemical Test.=—The metabolism undergone by food in the body
being essentially a process of oxidation (though partially modified
and incomplete), the amount of heat yielded on complete combustion of
a food may be taken as a measure of its value as a source of energy,
of which heat and work are convertible forms. The standard of heat
production is the =calorie=, the amount of heat required to raise the
temperature of one gramme of water 1° C. This is the small calorie.
The kilo-calorie (called the =Calorie=) is the amount of heat required
to raise 1 kilo (1 litre) of water 1° C., or 1 lb. of water 4° F. In
calculations on this basis, allowance must be made for foods which are
incompletely oxidised in the body. Rubner has shown that the heat value
of 1 gramme (=15½ grains) of each of the chief food stuffs is as
follows:—
Proteid 4.1 Calories.
Carbohydrates 4.1 „
Fat 9.3 „
The method of applying this standard to a food is as follows: the
percentage of proteid or carbohydrate given in the following table is
multiplied by 4.1, and the percentage of fat by 9.3:—
┌────────────────────────────┬──────────────────────────────────────────┐
│ │ IN 100 PARTS. │
│ ├──────┬────────────┬─────┬────────┬───────┤
│ │WATER.│ALBUMINATES │FATS.│ CARBO─ │ SALTS.│
│ │ │OR PROTEIDS.│ │HYDRATES│ │
├────────────────────────────┼──────┼────────────┼─────┼────────┼───────┤
│_Uncooked meat with little │ │ │ │ │ │
│ fat_ │ 74.4 │ 20.5 │ 3.5 │ ─ │ 1.6 │
│_Cooked meat─without loss_ │ 54 │ 27.6 │15.45│ ─ │ 2.95 │
│_Salt beef_ │ 49.1 │ 29.6 │ 0.2 │ ─ │ 21.0 │
│_White fish_ │ 78.0 │ 18.1 │ 2.9 │ ─ │ 1.0 │
│_Bread, white wheaten_ │ 40. │ 8. │ 1.5 │ 49.2 │ 1.3 │
│_Wheat flour_ │ 15. │ 11. │ 2. │ 70.3 │ 1.7 │
│_Rice_ │ 10 │ 5 │ .8 │ 83.2 │ 0.5 │
│_Oatmeal_ │ 15 │ 12.6 │ 5.6 │ 63.0 │ 3. │
│_Peas (dry)_ │ 15 │ 22 │ 2. │ 53. │ 2.4 │
│_Potatoes_ │ 74 │ 1.5 │ .1 │ 23.4 │ 1. │
│_Butter_ │ 8 │ 2. │88 │ ─ │variable│
│_Eggs (including shell, for │ │ │ │ │ │
│ which deduct 10 per cent.)_│ 73.5 │ 13.5 │11.6 │ │ 1 │
│_Cheese_ │ 36.8 │ 33.5 │24.3 │ ─ │ 5.4 │
│_Milk_ │ 87.0 │ 4. │ 3.5 │ 4.8 │ .7 │
└────────────────────────────┴──────┴────────────┴─────┴───────┴────────┘
Thus for bread—
Proteid 8 × 4.1 = 32.8
Fat 1.5 × 9.3 = 13.95
Carbohydrate 49.2 × 4.1 = 201.72
——————
Total Caloric value of 100 grammes of bread = 248.47
The total fuel value in Calories of one pound of certain typical foods
is given by Hutchison as follows:—Butter 3,577, peas 1,473, cheese
1,303, bread 1,128, eggs 739, beef 623, potatoes 369, milk 322, fish
(cod) 315, apples 238.
2. =The Physiological Test.=—Not only is a proper proportion of
proteid, fat, and carbohydrates required, but these must be capable
of digestion and absorption and of oxidation in the body. Cheese is a
highly concentrated food, but its value is less than its percentage
composition would indicate, because of the difficulty of digesting
considerable quantities of it. Green vegetables consist largely of
cellulose, which is only imperfectly capable of absorption into the
blood, although it can experimentally be oxidised by combustion. The
proportion between absorbed food and food rejected in the fæces can
be ascertained by analysis. Many experiments made on these lines show
that on a purely animal diet (meat, eggs, milk) but little nitrogen is
lost, while with vegetable foods (carrots, potatoes, peas, etc.) the
waste of nitrogen is considerable. Fats are very completely absorbed
from the alimentary canal. The amount remaining unabsorbed is greatest
with mutton fat (10 per cent.), least with butter (2½ per cent.).
Experimentally it has been found that an amount up to 150 grammes
(about 5½ oz.) of fat can be absorbed without appreciable loss.
Carbohydrates are very completely absorbed, even starchy foods rarely
escaping digestion. Completeness of absorption from the alimentary
canal is not desirable for all foods; a certain amount of unabsorbed
residue is required to stimulate peristalsis. With a purely vegetable
diet this amount is excessive, and there is physiological waste of
effort.
3. In practical dietetics =the Economic test= is important.
Carbohydrate is by far the cheapest food, and generally vegetable
are cheaper than animal foods. Thus a shilling’s-worth of bread
yields 10,764 Calories, while the same sum spent on milk would only
yield 1∕3, and on beef 1∕10 this number of heat units. Similarly a
shilling’s-worth of peas contains 572 grammes of proteid, about double
as much as the same money’s-worth of cheese; while to obtain the same
amount of proteid from eggs would cost more than eight, and from beef
more than five times as much as from peas (Hutchison). The market
price of foods is no certain indication of their nutritive value. Thus
haddock will supply as much nutriment as sole at a fourth of the cost;
Dutch as much nutriment as Stilton cheese at less than half the cost.
Similarly the most economical fats are margarine and dripping.
4. =An Examination of Actual Dietaries= under various conditions has
strikingly confirmed the results obtained by other methods. It has
been found that (_a_) the _potential energy_ required by a healthy man
weighing 11 stones, and doing a moderate amount of muscular work is
3,000 to 3,500 Calories (=310 grains); and that (_b_) about 20 grammes
of nitrogen and 320 grammes (=4,960 grains) of carbon are excreted
by such a man. (_c_) Expressing the 3,000 Calories required in terms
of grammes of food, it is found that 125 grammes of proteid, 500 of
carbohydrate and 50 of fat are necessary. These facts are expressed in
the following table (Hutchison):—
┌──────────────┬──────────────────┬───────────────────┬───────────────┐
│ │STANDARD AMOUNT OF│ SAME AMOUNT OF │ │
│ │FOOD CONSTITUENTS │ FOOD IN TERMS OF │YIELDING ENERGY│
│ │REQUIRED ├─────────┬─────────┤ IN CALORIES. │
│ │(IN GRAMMES). │ CARBON. │NITROGEN.│ │
│ ├──────────────────┼─────────┼─────────┼───────────────┤
│_Proteid_ │ 125 │ 62 │ 20 │ 512·5 │
│_Fat_ │ 500 │ 200 │ ── │ 2050· │
│_Carbohydrate_│ 50 │ 38 │ ── │ 465· │
│ ├──────────────────┼─────────┼─────────┼───────────────┤
│ │ 675 │ 300 │ 20 │ 3027·5 │
└──────────────┴──────────────────┴─────────┴─────────┴───────────────┘
Three of the best known standard dietaries give the amounts in grammes
of each food constituent as follows:──
┌──────────────┬─────────────┬─────────────┬─────────────┬────────────┐
│ │ PLAYFAIR. │ MOLESCHOTT. │ ATWATER. │ AVERAGE. │
│ ├─────────────┼─────────────┼─────────────┼────────────┤
│_Proteid_ │ 119 │ 130 │ 125 │ 125 │
│_Fat_ │ 51 │ 40 │ 125 │ 72 │
│_Carbohydrate_│ 531 │ 550 │ 450 │ 510 │
├──────────────├─────────────┼─────────────┼─────────────┼────────────┤
│Calories │ 3140 │ 3160 │ 3520 │ 3273 │
└──────────────┴─────────────┴─────────────┴─────────────┴────────────┘
Expressing the same facts in English ounces instead of grammes, 4-2∕5
oz. of proteid, 2½ oz. of fat, and 18 oz. of carbohydrate, would
represent the ounces of each constituent required according to
(1) (2)
┌────────────────────┬────────────────┬────────────────┐
│ │AVERAGE OF ABOVE│ HUTCHISON. │
│ │THREE DIETARIES.│ │
│ ├────────────────┼────────────────┤
│_Proteid_ │ 4-2∕5 │ 4-2∕5 │
│_Fat_ │ 2-1∕2 │ 1-4∕5 │
│_Carbohydrate_ │ 18 │ 17-3∕5 │
├────────────────────├────────────────┼────────────────┤
│_Ounces of dry food_│ 24-9∕10 │ 23-4∕5 │
└────────────────────┴────────────────┴────────────────┘
The chief point of divergence in the above standard dietaries is in
the relative proportion of carbohydrate and fat. Probably the correct
proportion between these is as 1 to 10; but it will vary according to
climate and other circumstances. Detailed examination of a large number
of dietaries shows that the amount of daily proteid should be about
125 grammes, or 4-2∕5 ozs. This is contained in 20 eggs, or in 18 oz.
_i.e._ about 4½ ordinary platesful of cooked meat.
It must be noted that the 23-24 oz. of food given above as the standard
daily amount represents dry food. This represents 40 oz. or nearly 3
lbs. of ordinary food.
The following example by Waller, gives a rather liberal standard
English diet, for a man doing a moderate amount of muscular work.
CARBON. NITROGEN.
_Foundation_: 1 lb. bread 117 5.5
1∕2 lb. meat 34 7.5
1∕4 lb. meat 84 —
_Accessories_: 1 lb. potatoes 45 1.3
1∕2 pint milk 20 1.7
1∕4 lb. eggs 15 2.0
1∕8 lb. cheese 20 3.0
——— ————
Total 335 21 grammes.
This divided up into meals works out roughly as follows (Hutchison):—
{Two slices of thick bread and butter.
Breakfast {Two eggs.
{One plateful of potato soup.
Dinner {A large helping of meat with some fat.
{Four moderate sized potatoes.
{One slice of thick bread and butter.
Tea A glass of milk and two slices of thick bread and butter.
Supper Two slices of thick bread and butter and 2 oz. of cheese.
From the preceding data, practical problems as to dietaries are easily
solved. Thus if it be required to find
_how much oatmeal, milk, and butter would be required to give a
sufficient quantity of albuminoids, fats, and carbohydrates to an
adult male_,
the calculation may be based on the figures in the table on p. 32, or
the following figures may, for the sake of convenient calculation, be
taken as representing the percentage amount of each of these chief food
principles contained in the foods named:—
ALBUMINOIDS. FATS. CARBOHYDRATES.
Oatmeal 12 6 60
Milk 4 3 5
Butter 2 88 —
Let o = number of ounces of oatmeal required.
m = „ „ milk „
b = „ „ butter „
Then (12o + 4m + 2b)∕100 = 4.5 ozs. of albuminoid
(6o + 3m + 88b)∕100 = 3 ozs. of fat
(60o + 5m)/100 = 14.25 ozs. of carbohydrate,
according to Moleschott’s diet.
When these equations are worked out by substitution and transference—
o = 19.2 ounces.
m = 55.4 „
b = 0.24 „
_Similarly if it is required to find how much meat, bread, and butter
of the following percentage composition will be required to give a man
a sufficient amount of albuminoids, fats, and carbohydrates._
ALBUMINOIDS. FATS. CARBOHYDRATES.
Meat 25 15 0
Bread 8 1.5 50
Butter 2 88 0
Let m = number of ounces of meat required.
b = „ „ bread „
B = „ „ butter „
Then 12m + 8b + 2B/100 = 4.5 ozs. of albuminoid
(15m + 1.5b + 88B)/100 = 3 ozs. of fat
50b/100 = 14.25 ozs. of carbohydrates
When these equations are worked out—
m = 6.28 ounces.
b = 28.5 „
B = 1.15 „
=Relation of Food to Mechanical Work.=—In the body the movements of
every part are constant sources of heat. It is evident therefore that
the potential energy of food can be expressed by (_a_) the amount of
heat obtained by its complete combustion, or (_b_) by the amount of
work capable of being obtained from it. Joule discovered by exact
experiment that the mechanical power obtainable from a given amount
of fuel is directly proportional to the amount of fuel used, being
in fact due to the oxidation of this fuel, the heat produced being
transformed into mechanical power. The _heat unit_ or calorie has been
already given (p. 32). The gram-metre is the _work unit_. The heat unit
corresponds to 425.5 units of work. Thus the same energy required to
heat one gramme of water 1° C. will raise a weight of 425.5 grammes to
the height of 1 metre. Conversely a weight of 425 grammes if allowed
to fall from a height of 1 metre, will by its concussion produce heat
sufficing to raise the temperature of 1 gramme of water 1° C. In
England the amount of work done is commonly expressed as foot tons,
_i.e._ tons lifted one foot; while in France it is similarly expressed
as kilogrammetres. Gramme-metres can be converted into foot-pounds
by multiplying them by .007233, and kilogrammetres into foot-tons by
dividing by 311.
Frankland estimated that—
1 oz. dry albumin yields 174 foot-tons of potential energy.
1 oz. fat „ 378 „ „
1 oz. starch „ 135 „ „
1 oz. cane sugar „ 129 „ „
1 oz. glucose or lactose „ 122 „ „
In practical dietetics digestibility of food as well as chemical
composition is an important factor. Furthermore metabolism in the body
is not in every instance so complete as oxidation outside it. Hence
estimates of potential energy can only be regarded as theoretically
correct. Examination questions like the following are occasionally
asked:—
A man does work equal to 176.8 foot-tons in a day. Supposing that he
eats only bread, how much will he require to give the amount of energy
required, if bread contains 8 per cent. proteid, 1.5 per cent. fat,
and 49.2 per cent. carbohydrate?
On the above basis, from 100 ounces of bread the amount of potential
energy obtainable is:—
8 × 174 = 1,392 foot-tons
1.5 × 378 = 567 „
49.2 × 135 = 6,642 „
——-——
Total energy = 8,601 „ obtained from 100 ozs. bread.
Let _b_ = number of ounces of bread required to develop 176.8
foot-tons of energy.
Then 8,601: 100:: 176.8: _b_.
Therefore _b_ = +2.05 ounces+.