Food and nutrition.pdf

Function of FoodDietary SourcesThe main sources of vitamin C in most diets are fruits, vegetablesand various leaves. In pastoral tribes milk is often the main source.Plantains and bananas are the only common staple foods containing fairquantities of vitamin C. Dark green leaves such as amaranth and spinachcontain far more than pale leaves such as cabbage and lettuce. Rootvegetables and potatoes contain small but useful quantities. Young maizeprovides some ascorbic acid, as do sprouted cereals and pulses. Animalproducts such as meat, fish, milk and eggs contain small quantities.As vitamin C is easily destroyed by heat, prolonged cooking of anyfood may destroy much of the vitamin C present.Ascorbic acid is measured in milligrams of the pure vitamin.Human RequirementsOpinions regarding human requirements differ widely. It seems clearthat as much as 75 mg per day is necessary if the body is to remain fullysaturated with vitamin C. However, individuals appear to remain healthyon intakes as low as 10 mg per day. A recommendation of 25 mg for anadult, 30 mg for adolescents, 35 mg during pregnancy and 45 mg duringlactation seems to be a reasonable compromise.DeficiencyScurvy and the other clinical manifestations of vitamin C deficiencyare described in Chapter 19. Scurvy is not now a prevalent disease.Out1:?reaks have occurred in famine areas and recently in several refugeecamps in Africa. In its early stages vitamin C deficiency may lead tobleeding gums and slow healing of wounds.Vitamin DVitamin D is associated with prevention of the disease rickets and itsadult counterpart osteomalacia (softening of the bones). Rickets was formany years suspected to be a nutritional deficiency disease, and in certainparts of the world cod-liver oil was used in its treatment. However, itwas not until 1919 that Sir Edward Mellanby, using puppies, demonstratedconclusively that the disease was indeed of nutritional origin and that itresponded to vitamin D in cod-liver oil. Later it was proved that action ofsunlight on the skin leads to the production of the vitamin D used byhumans.PropertiesA number of compounds, all sterols closely related to cholesterol,125