No one element of food is more important for the needs of the body than water. It comprises about two-thirds of the body weight and is a component part of all foods. It is composed of oxygen and hydrogen.
In order that the body may do efficient work in digestion and in the distribution of the nutrient elements of the foods, and that the evaporations from the body may be re-supplied, the water in the foods, together with the beverages drunk, should consist of about seventy-five per cent liquid to twenty-five per cent nutrient elements, or about three times as much in weight as proteins, fats, and carbohydrates combined. If undue evaporation or perspiration is occasioned, a larger proportion is required.
Water passes directly into the circulation without chemical change. It is being constantly evaporated through the lungs and the skin, and every forty-five seconds it passes from the kidneys into the bladder.
The average individual at normal exercise, requires about seventy-one and one-half ounces of water daily, which equals about nine glasses (one glass of water weighs one-half pound); a part of this is consumed in the food. By reference to the following tables it will be noted that water forms a large percentage of all food, particularly of green vegetables and fruits.
The importance of water for children must not be overlooked. It is the heat regulator of the body, and the more energy used, either in work or in play, which results in more heat and evaporation, the more water is required. An animal, if warm, immediately seeks water.
The body will subsist for weeks upon the food stored about its tissues; it will even consume the tissues themselves, but it would burn itself up without water, and the thirst after a few days without water almost drives one insane. It should be furnished freely, in small quantities at a time, to fever patients.
Few people, give much thought to its re-supply; yet they suffer from the loss of it, in imperfect digestion and assimilation, and with kidney and intestinal difficulties, ignorant of the cause.
Water softens and dissolves the food and aids in its absorption; it is one chief agent in increasing the peristaltic action of both the stomach and intestines, thus aiding in mixing the food with the digestive juices and aiding the movement along the alimentary canal; it increases the flow of saliva and of digestive juices and aids these juices in reaching every particle of food more promptly; it aids in the distribution of food materials throughout the body, carrying them in the blood and the lymph from the digestive organs to the tissues, where they are assimilated; it forms a large part of blood and lymph.
The theory has long been held that water drinking at meals is injurious, the objection being that the food is not so thoroughly masticated if washed down with water, and that it dilutes the digestive juices. But this theory is not so strongly held as formerly—in fact, it is now rightly disputed by the best authorities.
When water drinking at meals is allowed to interfere with mastication and is used to wash down the food, the objection is well taken, but one rarely drinks while food is in the mouth, the water being taken at rest periods between mouthfuls. Thorough mastication and a consequent free mixing of the food with saliva is one of the most essential steps in digestion, and the flow of gastric juice, as the flow of saliva, is stimulated by the water.