England, Germany, Italy, Russia, Sweden and
elsewhere in Europe, in Japan and other oriental countries, and
especially in the United States. These studies commonly consist in
ascertaining the kinds, amounts and composition of the different food
materials consumed by a group of persons during a given period and the
number of meals taken by each member of the group, and computing the
quantities of the different nutrients in the food on the basis of one
man for one day. When the members of the group are of different age,
sex, occupation, &c., account must be taken of the effect of these
factors on consumption in estimating the value "per man." Men as a rule
eat more than women under similar conditions, women more than children,
and persons at active work more than those at sedentary occupation. The
navvy, for example, who is constantly using up more nutritive material
or body tissue to supply the energy required for his muscular work needs
more protein and energy in his food than a bookkeeper who sits at his
desk all day.

In making allowance for these differences, the various individuals are
commonly compared with a man at moderately active muscular work, who is
taken as unity. A man at hard muscular work is reckoned at 1.2 times
such an individual; a man with light muscular work or a boy 15-16 years
old, .9; a man at sedentary occupation, woman at moderately active
muscular work, boy 13-14 or girl 15-16 years old, .8; woman at light
work, boy 12 or girl 13-14 years old, .7; boy 10-11 or girl 10-12 years
old, .6; child 6-9 years old, .5; child 2-5 years old, .4; child under 2
years, .3. These factors are by no means absolute or final, but are
based in part upon experimental data and in part upon arbitrary
assumption.

The total number of dietary studies on record is very large, but not all
of them are complete enough to furnish reliable data. Upwards of 1000
are sufficiently accurate to be included in statistical averages of food
consumed by people in different circumstances, nearly half of which have
been made in the United States in the past decade. The number of persons
in the individual studies has ranged from one to several hundred. Some
typical results are shown in Table IV.

7. _Quantities of Nutrients needed._--For the proper nourishment of the
body, the important problem is how much protein, fats and carbohydrates,
or more simply, what amounts of protein and potential energy are needed
under varying circumsta