In infancy, milk is the food of the child until its ninth month. During its first year a child takes approximately 125 gallons (1000 lb.) of milk. A child takes 1/7 its weight in food daily. In a year it has gained 13 lb. Of the 1000 lb. of milk 130 lb. are milk-solids (40 P- 40 F- 50 sugar), which build the child-body 13 lb., supply its heat and energy for its activity. For every pound of food that has gone into building the body, 9 lb. have been used in living the life.

With childhood's second year the food-need changes to one of growing variety in food. Milk continues as part of its diet, but a decreasing part, until in adult life milk becomes principally a food-ingredient. If in adult life milk is used as a beverage, it must be regarded as a substantial factor in the diet. The foods with which it is combined must supplement, not duplicate milk in composition, or the body will be overburdened with unneeded food. In illness, when activity is lessened, milk then often fully meets the body-need for sustenance and reenforcement of physical resistance. Milk is deficient in energy-giving power. It is a building and tissue-repair food in liquid form.

In made foods milk as an ingredient increases the nutritive value and palatability. Used as a cooking-liquid in substitution for water, it increases richness and fineness of texture.

In composition milk is nearly 9/10 water (87.1%). It contains 4% protein, 4% fat, 5% sugar, 1% mineral matter. In adult-diet even a light diet or narrow ration (that is, a diet in which there is little carbohydrate in proportion to protein) contains 2 1/2 times as much carbohydrate as protein. In milk the sugar (carbohydrate) is only 1/4 more. Were adults to attempt to live on milk they would take an excess of water (children need more proportionally) and more protein and fat than the body can stand, in order to get the carbohydrate it needs.