What Are The Dietary Constituents And Their Functions Within The Body?

This article is about the substances carbohydrates, proteins, fats, vitamins, mineral salts, water . Many foods contain a number nutrients. A balance diet is essential for health. It provides all nutrients in the correct proportions to meet the requirements of the body cells. An essential nutrient is a substance that cannot be made by human body an must therefore be included in the diet.

(1) Carbohydrates
(2) Proteins
(3) Fats
(4) Vitamins
(5) Mineral salts
(6) Fibre
(7) Water

(1) Carbohydrates:
These are found in a wide variety of foods, e.g, cereals, sugar, jam, bread, biscuits, pasta, convenience foods vegetables and fruits. They consists of carbon, hydrogen and oxygen, the hydrogen and oxygen being in the same proportion as in water.
Functions of digestible carbohydrates:
• Provision of a store of energy when carbohydrates is eaten in excess of the body's needs as it is converted to fat and deposited in the fat depots, e.g. under the skin.
• When there is an adequate supply of carbohydrates in the diet, protein does not need to be used to provide energy and heat.
• Provision of rapidly available energy and heat.

(2) Proteins:
Proteins are made up of a large number of units called amino acids linked together chemically. Proteins are broken down into their constituent amino acids by digestion and it is in the form that they are absorbed through the intestinal wall. Dietary protein is the only source of nitrogen that is usable in the body.
Functions of proteins:
• Synthesis of enzymes, plasma proteins, antibodies and some hormones.
• Growth and repair of body cells and tissues

(3) Fats:
Fats consist of hydrogen, carbon and oxygen, but they differ from carbohydrates in that the hydrogen are not in the same proportion as in water. Fats are divided into two groups, saturated and unsaturated.

Functions of fats:
• Support of certain body organs,e.g. the kidneys, the eyes.
• Transport and storage of the fat-soluble vitamins: A, D, E, K.
• Storage of energy as fat in adipose tissue under the skin and in the mesentery, when eaten in the excess of requirements.
• Production of chemical energy and heat

(4) Vitamins:
Vitamins are chemical compounds required in very small quantities which are essential for normal metabolism and health. Vitamins are divided into two main groups:
• Fat-soluble vitamins: A, D, E and K.
• Water-soluble vitamins: B complex, C.
Fat-soluble vitamins

Vitamin A:
This vitamin is found in such foods as cream, egg yolk, liver, fish oil, milk, cheese, and butter. Deficiency causes night blindness, drying and ulceration of cornea, slow and faulty development of bones.

Vitamin D:
The antirachitic vitamin is found mainly in animal fats such as eggs, butter, cheese, fish liver oils. Vitamin D regulates calcium and phosphorus metabolism and is therefore associated with the calcinations of bones and teeth. Deficiency causes rickets in children and and osteomalacia in adults, due to deficient absorption and utilisation of calcium and phosphorus. Humans and other animals can synthesise vitamin D by the action of the ultraviolet rays of the sun on a form of cholesterol in the skin.

Vitamin E:
Vitamin E are found in nuts, egg yolk, wheat germ, whole cereal, milk and butter and the daily requirement is about 3 to 4 mg. Deficiency associated with mild haemolytic anaemia.

Vitamin K:
The sources of vitamin K are fish, liver, leafy green vegetables and fruits.It is necessary for the formation by the liver of prothrombin and factors VII, IX and X, all essential for clotting of blood.Deficiency causes defective blood coagulation.

Water-soluble vitamins:

Vitamin B:
Vitamin B consists of a group of water-soluble vitamins that promote activity of enzymes at various stages in the chemical breakdown of nutrients to release energy.

Vitamin C:
Vitamin C is found in fresh fruit, especially blackcurrants, oranges, grapefruit and lemons, and in green vegetables.The daily requirement is 40 mg and after 2 to 3months, deficient intake becomes apparent. Deficiency includes:
• Swollen and spongy gums
• Anaemia
• Haemorrhage under the skin and into joints
• Delayed wound healing.

(5) Mineral salts:
Mineral salts are necessary within the body for all body processesThe main elements involved are:

This is found in milk, cheese, eggs, green vegetables and some fish. An adequate supply should be obtained in a normal, well balanced diet. It is associated with vitamin D and phosphorus in the hardening of bones and teeth, so an adequate supply in young people is important.

Sources of phosphorus includes cheese, oatmeal, liver and kidney. It is associated with calcium and vitamin D in the hardening of bones and teeth and helps to maintain the constant composition of the body fluids.

Sodium is found in most foods, especially fish, meat, eggs, milk, artificially enriched bread and as cooking table salts.

This substance is to be found widely distributed in all foods, especially fruit and vegetables. The normal intake of potassium chloride is 3.5g per day and this is in excess of potassium requirements.

Iron , as a soluble compound, is found in liver, kidney, beef, egg yolk, whole meal bread and green vegetables.

Iodine is found in salt-water fish and in vegetables grown in soil containing iodine. The daily requirement of iodine depends upon the individual's metabolic rate. Some people have a higher metabolic rate than others and their iodine requirements are greater.

(6) Fibre:
Fibre is the indigestible part of the diet that comes from plants and meat. It is distributed in wholemeal flour, the husks of cereals and vegetables.
Functions of fibre:
• Increases frequency of defaecation preventing constipation.
• Prevent some gastrointestinal disorders, e.g. diverticular disease.

(7) Water:
Water is a liquid compound of hydrogen and oxygen formed by the chemical combination of two parts by hydrogen and one part of oxygen.
Functions of water:
• Dillution and moistening of food.
• Participation in all the chemical reactions which occur inside the body cells.
• Dillution of waste products and poisonous substances in the body.
• A major constituent of blood and tissue fluid it transports some substances in solution and in suspension round the body.

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