Principles of Nutrition – Protein

The word protein comes from the Greek word meaning “of prime importance”. Next to water, protein is the most plentiful substance in the body. Protein is necessary for the maintenance of good health and vitality and is of primary importance in the growth and development of all body tissues. It is the major source of building material for muscles, blood, skin, hair, nails, and internal organs, including the heart and the brain.

Protein is needed for the formation of hormones, which control a variety of body functions such as growth, sexual development, and rate of metabolism. Protein also helps prevent the blood and tissues from becoming either too acid or too alkaline and helps regulate the body’s water balance. Enzymes, substances necessary for physiological reactions in the body, and antibodies, which are part of the immune system, are also formed from protein. In addition, protein is important in the formation of milk during lactation and in the process of blood clotting.

As well as being the major source of building material for the body,l protein may be used as a source of energy,l providing 4 calories per gram of protein. However, this energy-producing function is spared when sufficient fats ad carbohydrates are present in the diet. Excess protein in the diet that is not used for building tissue or energy productions is converted by the liver into fat for storage.

During digestion, the large molecules of proteins are broken down into simpler units called “amino acids”. These amino acids are than used to make body proteins and tissues. The body requires 22 amino acids to make human protein. All but 8 of these amino acids can be produced in the adult body (9 in children). The 8 that cannot be produced are called “essential amino acids” because they must be supplied in the diet. In order for the body to properly synthesize protein, all the essential amino acids must be present in the diet, in proper amounts. If just one essential amino acid is missing from the diet, protein synthesis will be greatly reduced.

Foods containing protein may or may not contain all the essential amino aids. If a food contains all of the essential amino acids, it is termed a “complete protein food”.  Foods that lack or are extremely low in any one of the essential amino acids are foods called “incomplete protein” foods.  Dairy products, eggs, fish, meat, poultry and soy beans are complete-protein foods, while most vegetables and fruits are incomplete protein foods.  To obtain a complete protein  meal from incomplete prtoeins, you must combine foods carefully so that those lacking an essential amino acid will be balanced by those adequate in the same amino acid (e.g. bread plus peanut butter).  Thus eating a balanced diet will promote protein synthesis to build muscle and repair damaged tissue following exercise.

Loss of body protein can occur from malnutrition, excessive bleeding, prolonged illness, or prolonged, intense exercise.  During these times of stress it is necessary to consume extra protein in order to repair damaged tissues.  However excessive intake of protein may cause fluid imbalance and will eventually be stored in the body as fat tissue.