tabulation of food values in terms of calories and the investigation of
the calorie needs of men and women in various occupations has been one of
the great contributions of the past twenty years of nutritional study and
to the progress made we owe our power to produce proper rations for every
type of worker. Army rations for example are built up of foods that will
yield enough calories to supply the needs of a soldier and during the
recent war extended studies conducted in training camps all over the
United States have shown that when the soldier eats all he wants he will
consume on the average about 3600 calories per day. In France the American
soldier's ration was big enough to yield him 4200 calories per day if he
ate his entire daily allowance.

But calories are not the only necessities. A pound of pure fat will yield
all the calories a soldier needs in a day but his language and morals
wouldn't stand the strain of such a diet. Neither would his health, for
not only does his body demand fuel but also that it be of a special kind.
While there are many kinds of foodstuffs, chemical analysis shows that
they are mainly combinations of pure compounds of relatively few
varieties. The chemists call these proteins, fats, carbohydrates, and
salts. Meats, eggs, the curd of milk, etc., are the principal sources of
protein. Sugars and starches are grouped together under the name of
carbohydrate. By salts is meant mineral matters such as common salt, iron
and phosphorus compounds, etc. In selecting foods it was found that the
body required that the proportions of these four substances be kept within
definite limits or there was trouble. We know now that a man can get along
nicely if he eats 50 grams of protein per day and makes up the rest of his
calories in carbohydrates and fats, provided that to this is added certain
requirements in salts and water.

It is also obvious that the foods given must be digestible and palatable.