Constituents of food

The body needs food to provide energy. Vitamins and minerals are necessary to maintain good health. The main food groups are carbohydrate, fat and protein. In addition, water is essential to replace fluid, which is continually being lost by the body. There are in total six essential foodstuffs with which the body must be constantly supplied, each of which are examined here in turn.

Essential foodstuffs are:

• carbohydrate

• mineral salts

These foodstuffs must be digested and absorbed. Food must therefore be of such a nature that it can be digested, i.e. broken down by digestive juices into substances that can pass into the bloodstream, and be carried to various tissues for their use.


The foods required for energy and heat within the body are called carbohydrate foods because they contain carbon, hydrogen and oxygen. Carbohydrates include sugar and starch and they are the chief source of body fuel.


Fatty foods provide energy and heat, which serve as body fuel. Fats also provide food stores, the adipose tissue of the body and protective coverings for some organs. It is recommended that dietary fat should account for less than 35% of total energy intake.


Proteins are the most complicated foodstuffs, containing nitrogen in addition to hydrogen, carbon, oxygen and in some cases sulphur and phosphorus. They are called nitrogenous foodstuffs as they are the only ones which contain the element nitrogen. Protein is necessary in the diet to build and replace the protoplasm of body cells. Proteins are composed of polypeptides, derived from amino acids. There are 20 amino acids, although each protein contains only some of these. Humans require approximately 0.75 g of protein per kg of body weight per day.


Water is essential for life as it forms nearly two-thirds of the human body and is present in most of the foods we eat. The average amount of water in the human body is about 45 litres (30 litres inside the cells - intracellular - and 15 litres outside the cells - extracellular - i.e. tissue fluid in the plasma). The main functions of water in the body are:

• excretion of waste products

• making digestive and lubricating fluids

• building of body tissues and body fluids

• temperature control (i.e. evaporation of sweat)

If the body is depleted of fluid the signs and symptoms of dehydration may appear; these include:

• slack elastic skin

• low blood pressure

The body requires 2-3 litres of water every day and the amount of fluid taken into the body must be balanced by the output.

Mineral salts

Mineral salts are essential for normal metabolism. Salts are produced by the action of an acid on a mineral.

An electrolyte is a dissolved salt (a mineral salt), which is capable of conducting electricity. The two major electrolytes are sodium (Na+) and potassium (K+). The concentration of Na+ is high in extracellular sites and low within cells (intracellular). In contrast K+ is low in tissue fluids and high within cells. A correct balance of electrolytes is essential for normal function of body tissues and fluids.

Sodium is present in all tissues; it exists as sodium chloride in a concentration of nine grams per litre (0.9%) in all extracellular fluids. Sodium is derived from our food, particularly animal foodstuffs, and from the rock salt used in cooking.

Potassium is present in all tissue cells, where it replaces the sodium of blood and tissue fluids and the source of the positively charged ions. Potassium is obtained from food, particularly plant foodstuffs.

Calcium is present in all tissues, particularly in bone, teeth and blood, and is necessary for the functioning of nerves and for muscle tone. It is obtained chiefly from milk, cheese, eggs and green vegetables. Adults require 400-500 mg daily.

Iron is essential for the formation of the haemoglobin in red blood cells. It is obtained from green vegetables, particularly spinach and cabbage, egg yolk and red meats. Men require 10 mg daily; women require more, 10-15 mg daily, because of menstrual blood loss.

Iodine is required for the formation of thyroxin by the thyroid gland. It is obtained from seafood and is also present in green vegetables.

Calcium, iron and iodine are the only minerals which may be insufficient in the diet.


Vitamins are also essential to normal health because they are necessary for a range of metabolic functions; they are of no value to the body as a fuel or as building material. Vitamins are present in small quantities in living foodstuff and are only required in minute traces each day. Vitamins are classified as fat soluble and water soluble; vitamins A, D, E and K are fat soluble, the other vitamins including B and C are soluble in water.

Vitamin A is present in all fatty foods, e.g. milk, cheese and fish liver oils. It can be made in the body from a substance called carotene, which is present in carrots and tomatoes. Vitamin A is needed for normal function of the retina and to fight infection. Correspondingly a lack of vitamin A causes visual loss, stunted growth and a lowered resistance to infection.

Vitamin D is found in dairy produce and also in fatty fish such as herring. Cod liver oil and halibut liver oil are very rich in vitamin D. Vitamin D can also be built up in the body; the ultraviolet rays from the sun act on a fatty substance in the skin called ergosterol, which produces vitamin D. Vitamin D is necessary, with calcium, for the formation of bone. Lack of vitamin D and/ or calcium leads to rickets in childhood, osteomalacia and osteoporosis in adults.

Vitamin E is present in vegetable oils and is found in egg yolk and milk. Vitamin E is necessary for normal functions of the nervous system, reproduction and muscle development.

Vitamin K is fat soluble and can be obtained from green vegetables and liver. It is required for the production of blood clotting factors in the liver. Vitamin K is synthesised in the intestine by colonic bacterial action.

Vitamin B is a complex of several closely related compounds. These are found particularly in the husks and germs of cereals and pulses, in yeast and yeast extracts and to a lesser extent in vegetables, fruit, milk, eggs and meat. The chief factors in the vitamin B complex are:

• Vitamin B1 (thiamine) is essential for carbohydrate metabolism and controls the nutrition of nerve cells.

• Vitamin B2 (riboflavin) is essential for the proper functioning of cell enzymes.

• Vitamin B6 (pyridoxine) is necessary for protein metabolism.

• Vitamin B12 (cyanocobalamin) is the anti-anaemic substance or factor absorbed by the villi of the small intestine and stored in the liver. It is satisfactorily absorbed only in the presence of intrinsic factor produced by the cells in the lining of the stomach. Vitamin B12 is essential for the proper development of red cells in the red bone marrow and of nervous tissue.

Folic acid is required in the body for the maturation of red blood cells. It is derived from green vegetables.

Vitamin C (ascorbic acid) is water soluble and is found in citrus fruits (oranges, grapefruits and lemons), green vegetables and potatoes. Vitamin C is important in tissue respiratory activity, wound repair and resistance to infection, and it affects the condition of capillary walls. Lack of vitamin C causes scurvy, a condition which used to be common in sailors on long sea voyages. Scurvy is occasionally seen today in older people who have not been feeding themselves properly.

Roughage is an indigestible part of food. It remains in the bowel and stimulates it to empty itself. Roughage is the fibrous part of food, giving it bulk and stimulating bowel action, thus preventing constipation.

Weight Loss Funnel

Weight Loss Funnel

Who Else Wants To Discover The 3 Most Effective Fat Burning Methods The Weight Loss Industry Does NOT Want You To Know About.

Get My Free Ebook

Post a comment