418 
DIGESTIVE ORGANS AND FOOD 
of people in a city and the average amount of work done, it 
is possible to estimate how much food must be sent to this 
city to keep the people alive and to enable them to do their 
work. The adoption of the calorie unit thus serves to intro¬ 
duce accuracy into all calculation of food uses. 
What the daily calorie needs are : 
For a workingman 3500 to 4000 
For an active woman 2800 to 3000 
For a sedentary man 2200 to 2800 
For a sedentary woman 1800 to 2300 
Youth 14 to 16 years 1500 to 3200 
Active soldier 4000 
One must keep in mind that our bodies require energy to 
grow new cells and to keep the old ones in repair; to keep the 
body at a constant temperature winter and summer; and 
to furnish energy for muscular activity, which often requires 
more energy than to carry on growth and maintain a constant 
temperature. To meet these needs of every human being 
a variety of foods is needed. 
In the classification of foods given on page 13 into proteins, 
carbohydrates, fats, mineral matter, and vitamines, the 
arrangement is made upon their chemical composition be¬ 
cause foods do not grow as proteins or fats. The foods that 
we eat are often composed of all these. There are five food 
groups which are arranged chiefly on the proportionate 
amounts of proteins, sugars, or fats. These are shown in the 
table on the following page. 
A well-balanced diet contains a proper proportion of these 
five food groups. One food from each of these groups should 
be used each day. It is impossible to prescribe an exact 
diet for every one, as it should vary with the age, weight, 
health, occupation, and location of the individual. The 
variation, however, is largely in the quantity rather than in 
the kind used. 
