It has been estimated that the average daily need of the adult is forty-five ounces of solid food, one-fourth animal and three-fourths vegetable. Twice as much water as solids should be taken.
The laborer, engaged in heavy muscular activity, needs and can assimilate more than the sedentary office worker. Those who work but a few hours a day require less food, as a rule, than those who work long hours.
Cold weather demands more heat-producing foods; a hot climate, inducing inactivity of body, diminishes the need for food.
The invalid needs less food than the healthy.
The inhabitant of the frigid zone needs much fat; he who lives in the tropics but little fat.
The old need less food than the growing youth or the hearty adult.
The poor must often take what he can get while the rich eat to satiety. Yet all these food needs vary with the individual and with the sex and activity.
It has been computed that the system needs daily three hundred grains of nitrogen and four thousand eight hundred grains of carbon. To obtain this amount of nitrogen if bread alone were eaten it would require four pounds of bread from the whole wheat. The carbon in this amount of bread largely exceeds that required. If eaten alone, six pounds of beef would be necessary to supply the proper amount of carbon, and twenty-three pounds of eggs. The nitrogen in this amount would far exceed the requirement.
One pint of milk, 21/2 ounces of bread, and six ounces of beef are about equal in nutritive value.
One can see, therefore, why a diet composed of too great a quantity of one substance gives an overbalance of one and an underbalance of another.