NUTRITION

Nutrition

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Nutrition

Definition of Nutrition:

Nutrition is the study of the materials that nourish an organism and of the manner in which the separate components are used for maintenance, repair, growth, and reproduction. Nutrition is achieved in various ways by different forms of life. Plants that contain the green pigment chlorophyll can synthesize their food from inorganic substances in the process called photosynthesis. Organisms such as plants that can thus manufacture complex organic compounds from simple inorganic nutrients are termed autotrophic. Organisms that must obtain "prefabricated" organic compounds from their environment are heterotrophic, and these include the fungi, some other plants, and animals. Heterotrophic plants may be saprophytic (obtaining nutrients from dead organisms) or parasitic (obtaining nutrients from living organisms while living on or in them). Heterotrophic animals may be parasites, herbivores (plant eaters), carnivores (meat eaters), or omnivores (obtaining nutrition from both plants and animals).

HUMAN NUTRITION:

Humans require food substances to supply the components necessary to build tissues, to repair tissues as they wear out and die, to keep the body in good working condition, and to supply fuel for energy. For good nutrition a person should eat a well-balanced diet, that is, one that provides an adequate amount of each of the classes of nutrients each day, furnishing at the same time an adequate but not excessive number of calories for the body's energy needs. Children require relatively larger amounts of nutrients and calories because of their rapid growth. The foods required for proper nutrition fall roughly into three major groups: proteins, carbohydrates, and fats; vitamins, minerals, and water are also important.

PROTEINS:

Protein in the diet provides amino acids for forming body proteins, including the structural proteins for building and repairing tissues, and the enzymes for carrying out the metabolic processes. In addition, protein may be used as a source of energy when the preferred fat and carbohydrate supply runs low. A body that is in the process of building itself (such as that of a growing child or an adult recovering from illness) will need a greater proportion of protein to weight than one that is fully grown and utilizes protein merely for repair of worn-out tissues. The average adult requires 1 gram of protein per kilogram of body weight per day; children may require two to three times this amount. Human proteins consist of up to 22 different amino acids, of which 9 (called essential amino acids) must be supplied by food protein; the other 13 are synthesized by human cells. Complete protein sources--those foods containing all 22 amino acids--include animal products such as meat, eggs, cheese, and milk. Incomplete protein sources, such as vegetables, beans, and grains, may be combined to create complete proteins.

CARBOHYDRATES:

Carbohydrates (starches and sugars) provide a readily available energy source. Surplus carbohydrates are also converted by the body to glycogen and fat, the storage forms of calories for energy, and to some of the amino acids used in protein synthesis. Most health professionals recommend that carbohydrates comprise 50% to 60% of the dietary calories, ...