Food and nutrition.pdf

Function of Food 101of the constitution of many tissues. For example, calcium and phosphorusin bones combine to give rigidity to the whole body. Minerals are presentin body acids and alkalis; for example, chlorine occurs in hydrochloricacid in the stomach. They are also essential constituents of certainhormones, e.g. iodine in the thyroxine produced by the thyroid gland.The principal minerals in the human body are calcium, phosphorus,potassium, sodium, chlorine, sulphur, copper, magnesium, manganese,iron, iodine, fluorine, zinc, cobalt and selenium. Phosphorus is so widelyavailable in plants that a shortage of this element is unlikely in any diet.Potassium, sodium and chlorine are easily absorbed and arephysiologically more important than phosphorus. Sulphur is consumedby humans mainly in the form of sulphur-containing amino acids; thussulphur deficiency, when it occurs, is linked with protein deficiency.Copper, manganese and magnesium deficiencies are not believed to becommon. The minerals that are of most importance in human nutritionare thus calcium, iron, iodine, fluorine and zinc, and only these arediscusSed in some detail here. Some mineral elements are required in verytiny amounts in human diets but are still vital for metabolic purposes;these are termed "essential trace 'elements". .,~The table giving the nutrient content of selected foods shows therelative content of some important minerals in different foods.CalciumThe body of an average-sized adult contains about 1 250 g of calcium.Over 99 per cent of the calcium is in the bones and teeth, where it iscombined with phosphorus as calcium phosphate, a hard substance thatgives the body rigidity. However, although hard and rigid, the skeletonof the body is not the unchanging structure it appears to be. In fact, thebones are a cellular matrix, and the calcium is continuously taken up bythe bones and given back to the body. The bones, therefore, serve as areserve supply of this mineral.Calcium is present in the serum of the blood in small but importantquantities, usually about 10 mg per 100 ml of serum. There are also about10 g of calcium in the extracellular fluids and soft tissues of the adult body.Properties and FunctionsIn humans and other mammals, calcium and phosphorus togetherhave an important role as major components of the skeleton. They arealso important, however, in metabolic functions such as muscular function,nervous stimuli, enzymatic and hormonal activities and transport ofoxygen. These functions are described in detail in textbooks of physiologyand nutrition.