Nutritive Ingredients (or Nutrients) of Food
| Food as purchased contains: | Edible portion e.g., flesh of meat yolk and white of eggs wheat, flour, etc. Refuse. e.g., bones, entrails, shell, bran, cellulose, etc. | Water Nutrients— | Protein Fats Carbohydrates Mineral matters |
Uses of Nutrients in the Body
| Protein | Forms tissue | — | All serve as fuel to yield energy in the forms of heat and muscular power. | |
| e.g., white (albumen) of eggs | ||||
| curd (casein) of milk | ||||
| lean meat | ||||
| gluten of wheat, etc. | ||||
| Fats | Are stored as fat | |||
| e.g., fat of meat, butter, olive oil | ||||
| oils of corn, wheat, etc. | ||||
| Carbohydrates | Transformed into fat | |||
| e.g., sugar, starch, etc. | ||||
| Mineral Matters (ash) | Share in forming bone, assist in digestion, etc. | |||
| e.g., phosphates of lime | ||||
| potash, soda, etc. | ||||
Thus foods have different functions. The proteid or nitrogenous foods build up and repair the tissues; mineral matter and water are also necessary for this purpose. The tissues of the body cannot be kept in a healthy state unless these constituents of food are taken into the system regularly; only the proteid foods can repair the waste of the living tissue. The proteid foods, together with the fats and carbohydrates, may supply both power and heat for the body, but the special functions of the carbohydrates and fats are to keep the body warm and to supply energy.
The amount of proteid food required for a healthy adult is very difficult to determine. It is safe to state that too much proteid brings about undue strain upon the digestive apparatus, and that too little proteid reduces the working equipment of the body. The amount of fats and carbohydrates needed depend largely upon occupation and climate. The proteid foods are many, and contain the same chemical elements as the bodies which they are destined to feed; also they seem to be more completely taken care of in the body than the carbohydrate foods. Milk, cheese, eggs, meat, and fish are proteid foods. Of these milk is regarded as a typical food, as it contains all the nutritive constituents required by the body,—proteid, carbohydrates, fats, mineral matter, and water,—but it does not contain these constituents in the correct proportion. It is too rich in proteid and fat and too poor in carbohydrate to be a perfect food. It is a perfect food for the infant, because an excess of proteid and of fat is needed for the growth of the child. For the healthy man about eight pints daily would be required for complete nutrition. This, it is apparent, would be a very bulky food, and the system would be burdened with too large a proportion of water. Milk, on the other hand, is the cheapest source of proteid. It is claimed that one quart of good milk is equivalent in proteid to a pound of beefsteak, and that when combined with the correct proportion of carbohydrate food it possesses great nutritive and economic value. All of the proteid foods are deficient in starch, so must be combined with carbohydrates to properly nourish the body.
According to Mr. Atwater the proteid foods are more completely digested than the carbohydrates. This is probably because there is found in all carbohydrate foods a large proportion of cellulose or indigestible material enveloping the starch and sugar. The nutritive value of the carbohydrate foods is large if the starch and sugar, of which they are composed, can be separated from the cellulose. The normal diet is one which contains proteid foods, carbohydrate foods, fatty foods, with the correct proportion of mineral matter and sufficient water to moisten them.
The proper diet depends largely upon the occupation. People of sedentary habits and brain workers need more digestible food than the day laborer—therefore, the necessity of mixed diets; but diets should be varied as well as mixed, and the true housekeeper in planning meals thinks what was served at the preceding meal.
The cheapest diet is that which yields the largest amount of nutriment for the least expenditure of money. The most economical diet is that which is cheapest and at the same time best adapted to the needs of the user. The most expensive diet is not necessarily the most nutritious.