Of foods with little waste and large percentage of nutrients, eggs, milk, bread, are the most important. Though they are often called whole, entire, complete, or perfect foods, they are rather concentrated foods, universally used wherever their expense does not forbid. Only milk ever serves alone for human food, and it does so only in infancy for a limited period. But eggs, milk, bread, are concentrated foods of great value.

Eggs supply the materials from which chickens form. Until their activity begins, their need is for water, 74 %; nitrogen, 12%; fat, 10%; mineral salts, 1%. Part of the shell may be used as needed. The shell is porous; the air enters through it, which is used in the changes occurring as the chick forms in the egg. With the beginning of active life chickens need, and take so soon as they emerge from the shell, the meal-food that gives them energy. Like meats, eggs have no carbohydrate, but some fat, though not enough to sustain human activity with egg-foods.

Milk has carbohydrate that egg lacks, and meat has extractives. Meat contains the products of decomposition due to activity of animals; eggs do not. Egg-white contains about the amount of water in milk. Egg-solids are chiefly protein in the form of albumen; this is most digestible, especially raw. Egg-yolk contains more fat than is found in cream. (See p. 114.) Egg-salts, in both white and yolk, like those of milk, are of value, particularly for growing children.