16 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 
than the bread that the 6 pounds of potatoes furnish decidedly less 
protein and fat and slightly less carbohydrates than the 2 pounds of 
bread. It is easy, therefore, to see why, in spite of their cheap- 
ness and similar composition, they should not occupy the same place 
in the diet as bread. A diet of bread alone would be rather too one- 
sided for the best development of bodily powers, but would come 
nearer to supplying the required protein without excess of carbo- 
hydates than potatoes alone. 
With respect to the total nutritive material they supply, raw pota- 
toes resemble fresh fruits, such as bananas and apples, with their 
seven or eight parts of water to one of food substance, more than they 
do such foods as uncooked flour or rice, with their one part of water 
to nine of nutritive material. Since raw potatoes consist of only 
one-fifth and raw rice, for instance, of seven-eighths nutritive mate- 
rial, one would naturally say that rice is more than four times as 
nutritious as potatoes, and this is true of them as they are bought in 
the market. This, however, is not the case when they are compared 
in the state in which they appear on the table. When rice is cooked 
water is added to it, with the result that when it is eaten it is not 
very different in composition from cooked potatoes ; thus a pound of 
boiled rice and a pound of mashed potatoes would have very much 
the same total fuel value, a fact which has been intuitively recognized 
by housekeepers, who often use them interchangeably to serve with 
meats, etc. They do not, however, have the same effect on the 
alkalinhVy of body tissues and fluids. 
According to generally accepted standards, a man at moderately 
active work requires about one-fourth pound of protein a day, along 
with sufficient fats and carbohydrates to give the total food an energy 
value of about 3,500 calories. It would take about 9 pounds of 
potatoes to furnish this energy, but that quantity would yield much 
less protein than the amount called for by the standard. About 19 
pounds of potatoes would be needed to yield the required 0.25 pound 
of available protein, an obviously impossible bulk for a day's ration. 
Except under stress of necessity, however, few persons try to live 
entirely or even principally on potatoes. Ordinarily they are eaten 
with other foods rich in protein, such as meat,* milk, eggs, etc., and 
thus they supplement these nitrogenous foods by furnishing the 
needed carbohydrates in an easily digested form. 
The abundant mineral matters which they contain also supply the 
body with important building materials and help to regulate its proc- 
esses. As is the case with most vegetables and fruits, potatoes, when 
they have been digested and assimilated by the body, tend to make 
the tissues and fluids of the body more alkaline. Meats and eggs, 
on the other hand, tend to make them more acid, while the cereals 
(including rice) do not affect them greatly either way. Physiolo- 
