Food and nutrition.pdf

Function of Food 105world, both South and North. The average iron content in a healthy adultis only about 3 to 4 g, yet this relatively small quantity is vital.Properties and FunctionsMost of the iron in the body is present in the red blood cells, mainlyas a component of haemoglobin. Much of the rest is present in myoglobin,a compound occurring mainly in muscles, and as storage iron or ferritin,mainly in the liver, spleen and bone marrow. Additional tiny quantitiesare found binding protein in the blood plasma and in respiratory enzymes.The main, vital function of iron is in the transfer of oxygen at varioussites in the body. Haemoglobin is the pigment in the erythrocytes thatcarries oxygen from the lungs to the tissues. Myoglobin in skeletal andheart muscle accepts the oxygen from the haemoglobin. Iron is also presentin peroxidase, catalase and the cytochromes.Iron is an element that is neither used up nor destroyed in the properlyfunctioning body. Unlike some minerals, it is not required for excretion,and only very small amounts appear in urine and sweat. Minute quantitiesare lost in desquamated cells from the skin and intestine, in shed hair andnails and in the bile and other body secretions.The body is, however, efficient, economical and conservative in theuse of iron. Iron released when the erythrocytes are old and broken downis taken up and used again and again for the manufacture of newerythrocytes. This economy of iron is important. In normal circumstances,only about 1 mg of iron is lost from the body daily by excretion into theintestines, in urine, in sweat or through loss of hair or surface epithelialcells.Because iron is conserved, the nutritional needs of healthy males andpostmenopausal females are very small. Women of child-bearing age,however, must replace the iron lost during menstruation and childbirthand must meet the additional requirements of pregnancy and lactation.Children have relatively high needs because of their rapid growth, whichinvolves increases not only in body size but also in blood volume.Dietary SourcesIron is present in a variety of foods of both plant and animal origin.Rich food sources include meat (especially liver), fish, eggs, legumes(including a variety of beans, peas and other pulses) and green leafyvegetables. Cereal grains such as maize, rice and wheat contain moderateamounts of iron, but because these are often staple foods and eaten inlarge quantities, they provide most of the iron for many people, indeveloping countries. Iron cooking pots may be a source of iron.Milk, contrary to the notion that it is the "perfect food", is a poor