Nutrition includes all the processes by which a plant or animal obtains food and uses it. All substances which an organism can use to build protoplasm and produce energy are foods. Plants produce their own food from carbon dioxide, water, and minerals through photosynthesis. The foods of animals include organic materials made by plants or other animals, and water and minerals. Organic foods are of four types: carbohydrates, which include sugar and starches; proteins; fats; and vitamins. All animals, except a few parasites must capture their food. There are seven basic types of food needed for health.
Once an animal catches its food, it is digested or broken down into substances which are then distributed to the body cells. In man, water, water-soluble vitamins, and minerals need no digestion. Fat-soluble vitamins and digested fats are absorbed into lymph vessels in the small intestine. These vessels eventually join the circulatory system. Digested carbohydrates and proteins enter the capillaries in the small intestine.
Good nutrition depends upon getting adequate, but not excessive, amounts of every type of food. Among the necessary minerals are calcium and phosphorus needed for tooth and bone growth, iron needed for red blood cells, sodium and potassium needed for proper heartbeat, and iodine for thyroxin, a metabolic hormone. Traces of other minerals such as copper are also needed.
Water makes up about seventy per cent of the tissues of the body. It is constantly lost from the body and must be replaced.
Vitamins also play an important part in body functions. A certain amount of each of the kinds of vitamins seems to be important in maintaining the health of certain parts of the body or functions. Vitamins, minerals, and water are needed in smaller amounts than the other foods.
The human body must have proteins in order to grow, repair tissues, produce hormones and disease-fighting antibodies. All organic foods can supply energy to the body.
The most readily usable form of energy is provided by carbohydrate foods. However, one tablespoon of fat provides two and one-quarter times as much energy as a tablespoon of carbohydrates. Carbohydrates are the only food which can be almost totally eliminated from the diet.
