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Foods Classified

Foods are classified into five classes: proteins, fats, carbohydrates, mineral matter, and water, though some food substances do not properly belong in any of these classes.


  • Proteins contain carbon, hydrogen, oxygen, and nitrogen.
  • Fats contain carbon, hydrogen, and oxygen.
  • Carbohydrates contain carbon, hydrogen, and oxygen.
  • Water contains hydrogen and oxygen.

Mineral matter consists of compounds of iron, calcium, potassium, sodium, magnesium, sulfur, phosphorus, chlorine, and fluorine. These are associated with the proteins and carbohydrates in the various tissues and fluids of the body.

Proteins, mineral matter, and water build tissue; carbohydrates, fats, and proteins yield heat and energy.

Foods are also classified as animal and vegetable foods because of the sources from which they are derived. Examples of vegetable foods are potato, carrot, wheat, rice, peas, apple. Examples of animal foods are meat, fish, eggs, milk, cheese.

Structure of Foods.

All foods are similar in structure in that they are made up of innumerable cells held together by some inter-cellular substance. Each cell consists of two, sometimes three, parts — nucleus, protoplasm, and cell wall.

Every cell has a nucleus or center of life from which the cell grows and produces other cells. Surrounding the nucleus is the protoplasm or nourishment of the cell.

It supplies the material needed for the growth and development of the nucleus. It consists of protein, mineral matter, and water, as does also the nucleus. Protoplasm is more or less granular and forms a sort of network that may enclose other substances, as starch or fat. All vegetable cells, and some animal cells, have a cell wall. The walls of animal cells consist of a substance called connective tissue. This substance also holds the cells together. The cell walls of vegetable cells consist of a substance called cellulose. It is similar in composition to starch, but unlike it in structure. When it is old, it sometimes turns to wood. The human stomach cannot digest cellulose, and so it must be softened by cooking to allow for the digestion of the starch or fat which it encloses. Cellulose is of value, however, in that it furnishes bulk.

I. Carbohydrates.


1. Starch, as in potato, rice, corn and all vegetable foods.
Insoluble in cold water.

2. Sugar — cane, beet, maple, malt, fruit.s

3. Cellulose — cell walls of plants.

4. Pectin — found in fruits and some vegetables. Causes juice to gelatinize. Occurs also as pectose which is changed to pectin by the action of a ferment.

II. Vegetable Acids.

1. Malic, oxalic, citric, tartaric. Decomposition products of starch or sugar. They are decomposed in the body, forming alkaline carbonates, and help to preserve the alkalinity of the blood.

III. Proteins.


1. True proteins.

Coagulated by the heat or acid or ferment. Some are soluble in cold water, some in diluted salt, acid, or alkaline solution; some are insoluble.

Albumin as in egg. Casein as in milk. Myosin as in meat. Fibrin as in meat. Gluten as in wheat. Legume as in peas and beans.

2. Albuminoids.

Softened by moist heat and hardened by dry heat. Soluble in boiling water. Ossein in bone, elastin in cell walls, collagen in connective tissue.

3. Extractives. Soluble in water. They are the flavor in meat juice and in some vegetables.

IV. Fats.

Fats and Oils

1. Fixed fats. Softened by moderate heat, separated into fatty acid and glycerine by strong heat. Examples: butter, lard, olive oil.

2. Volatile oils. Found in orange and lemon skins, onions, etc. Soluble and volatile.




V. Mineral Matter.


1. Lime in milk, sulfur in eggs, phosphorus in wheat.
In proteins, sulfur, phosphorus, and iron.
In vegetables, potassium, sodium, magnesium, calcium.
Common salt.

VI. Water.