2 DEPARTMENT BULLETIN" 975, IT. S. DEPT. OE AGRICULTURE. 
fairly common. 1 There are, however, other essentials in the diet 
which can not be explained so easily. For example, it has been 
difficult to make helpful statements about the mineral matters, the 
more important of which are iron, calcium, and phosphorus. It 
is fairly well known how much of these are needed by the body and 
how much are found in different food materials, but in both cases 
the quantities are so small (only a few grams or even milligrams 
per man per day or per pound of material) that it is impracticable 
to measure them by pounds or ounces as we do the food materials 
that supply them. 
In general, the plan here followed is to make a graphic comparison 
between a pound of some of the common foods and the daily needs 
of a man who does moderately active muscular work. No one would 
think, of course, of trying to live on one food alone, but the com- 
parison made by the charts is helpful in combining food materials 
so as to make a complete ration, for it shows not only what a given 
food supplies but also what it lacks. The milk diagram (p. 20) is a 
good illustration. A glance at it shows that a pound (pint) of 
milk would supply 9 per cent of the energy or fuel, 15 per cent of the 
protein, 80 per cent of the calcium, 32 per cent of the phosphorus, but 
only 7 per cent of the iron needed daily by a man who does moder- 
ately active muscular work. Or, to put it another way, if a pint 
of milk is used in the daily dietary of this man, the remaining foods 
must supply 91 per cent of the fuel needed, 85 per cent of the protein, 
20 per cent of the calcium, 68 per cent of the phosphorus, and 93 per 
cent of the iron. To speak in particular only of the calcium and the 
iron, which offer a striking contrast, the remaining 20 per cent of the 
calcium would almost inevitably be supplied by the other foods even 
if they were selected at random, while it might require some thought 
to supply the other 93 per cent of the iron. 
In making these comparisons it is assumed that the food supply of 
a man who does moderateiV active muscular work should furnish 
3,500 calories of energy, or body fuel, 100 grams (3| ounces) of pro- 
tein, 0.68 gram of calcium, commonly called lime, 1.32 grams of 
phosphorus, and 15 milligrams of iron. This amount of food makes 
provision for waste, of which a certain amount is unavoidable. It 
is generally agreed that a properly nourished man doing moderately 
active muscular work eats daily food that supplies about 3,000 
calories, and that to be sure of supplying this amount the foods pro- 
vided for him should furnish about 3,500 calories. The allowance 
of 100 grams of protein provides a generous margin of safety above 
the actual protein requirement, and the allowances for calcium, 
1 U. S. Dept. Agr., Farmers' Bui. 142, Principles of Nutrition and Nutritive Value of 
Food ; Farmers' Bui. 808, How to Select Foods. I. What the Body Needs. 
