Page:Food and cookery for the sick and convalescent.djvu/27

Rh in many respects they are interchangeable. "In the diet of children, at least, a deficiency of fat cannot be replaced by an excess of carbohydrate; and that fat seems to play some part in the formation of young tissues which cannot be undertaken by any other nutritive constituent of food," is a prevailing belief among competent observers.

Water constitutes about two-thirds of the weight of the body, and enters into the composition of all the tissues and fluids. To keep the necessary proportion, a large quantity needs to be ingested. One of the great dietetic errors is the neglect to take a sufficient quantity. The amount found in foods is insufficient, and about five cupfuls should be taken daily in beverages. A vegetable diet diminishes the need of water, while one composed largely of animal food increases this need.

Mineral matter is necessary for the building of tissues, being found, principally, in the bones and teeth. It aids in the digestion of foods, and also assists in the diffusion of the fluids of the body. Phosphate of lime, or calcium phosphate, is the mineral basis of bones. Potassium, magnesium, sodium, and iron are minerals, all of which are essential to life. They usually enter the body in