35. FACTORS INFLUENCING FOOD.--Numerous factors affect the kind and
quantity of food necessary for an individual. Chief among these are age,
size, sex, climate, and work or exercise. In addition to determining the
amount of food that must be taken into the body, these factors regulate
largely the suitability of the foods to be eaten. It is true, of course,
that all the food substances mentioned in Table II must be included in
every person's diet after the first few years of his life, but the
quantity and the proportion of the various substances given vary with
the age, sex, size, and work or exercise of the person and the climate
in which he lives. Merely to provide dishes that supply sufficient food
value is not enough. This food material must be given in forms that can
be properly digested and assimilated and it must be in the right
proportion for the person's needs. The aim should therefore be to
provide a _balanced diet_, by which is meant one that includes the
correct proportion of the various food substances to supply the needs of
the individual.
36. QUANTITY OF FOOD IN CALORIES.--Without doubt, the most intelligent
way in which to feed people is to compute the number of calories
required daily. As will be remembered, the calorie is the unit employed
to measure the amount of work that the food does in the body, either as
a tissue builder or a producer of energy. The composition and food value
of practically all foods are fairly well known, and with this
information it is a simple matter to tell fairly accurately the amount
of food that each person requires.
As has been stated, the number of calories per day required by a person
varies with the age, size, sex, and occupation of the person, as well as
with the climate in which he lives. For the adult, this will vary from
1,800 to 3,000, except in cases of extremely hard labor, when it may be
necessary to have as high as 4,500 calories. The average number of
calories for the adult, without taking into consideration the particular
conditions under which he lives or works, is about 2,500. Still a small
woman who is inactive might be sufficiently fed by taking 1,800 calories
a day, whereas a large man doing heavy, muscular work might require
3,500 to 4,000 daily.
37. IMPORTANCE OF PROPER AMOUNT OF FOOD.--Most authorities agree that it
is advisable for adults and children well past the age of infancy to
take all the food required in three meals. The taking of two meals a day
is sometimes advocated, but the possibility of securing in two meals the
same quantity of food that would ordinarily be taken in three is rather
doubtful, since it is assumed that large amounts of food are not so
easily disposed of as are smaller ones.
On the other hand, to overeat is always a disadvantage in more respects
than one. Taking food that is not required not only is an extravagance
in the matter of food, but overtaxes the digestive organs. In addition,
it supplies the body with material that must be disposed of, so that
extra work on the part of certain organs is required for this activity.
Finally, overeating results in the development of excessive fatty
tissue, which not only makes the body ponderous and inactive, but also
deadens the quickness of the mind and often predisposes a person to
disease or, in extreme cases, is the actual cause of illness.
38. EFFECT OF WEIGHT ON DIET.--An idea of the way in which the weight of
a person affects the amount of food required can be obtained by a study
of Tables III and IV. As will be observed, Table III gives the number
of calories per pound of body weight required each day by adults engaged
in the various normal activities that might be carried on within 24 hours.
It deals only with activity, the various factors that might alter the
amounts given being taken up later. The figures given are for adults
and the factors mentioned are those which affect the intake of food
to the greatest extent.
The lowest food requirement during the entire 24 hours is during the
time of sleep, when there is no activity and food is required for only
the bodily functions that go on during sleep. Sitting requires more food
than sleeping, standing, a still greater amount, and walking, still
more, because of the increase in energy needed for these activities.
In a rough way, the various occupations for both men and women are
classified under three different heads: Light Work, Moderate Work, and
Heavy Work. It is necessary that these be understood in examining
this table.