Food and nutrition.pdf

86 Function of Foodaround body organs such as the intestine and heart. It serves in part as anenergy reserve. Small quantities are present in the walls of body cells orin nerves.Physiologists and those interested in metabolism have developedvarious ways to estimate body composition, including the amount of fluidsin the body and body density. A common determination is to estimatelean body mass (LBM) or the fat-free mass of the body. These measuresvary from the very simple to the very difficult. The simpler ones are ofcourse less precise. Anthropometry using weight, height, skinfoldthickness and body circumferences is relatively easy and very cheap toundertake, and does provide some estimate of LBM and body composition.In contrast, methods using, for example, bioelectrical impedance,computerized axial tomography (CAT scans) and nuclear magneticresonance require expensive apparatus and highly trained staff.The fluid in the cells (intracellular fluid) has mainly potassium ions,and the extracellular fluid is mainly a solution of sodium chloride. Bothalso have other ions. Total body water can be estimated using differentmethods including dilution techniques to measure, for e?,ample, plasmavolu .. ne.Body fat is estimated using different methods. Because a large portionof adipose tissue is present beneath the skin, it can be estimated by usinga skinfold calliper to measure skinfold thickness in different sites. Anothermethod is to weigh the person both in air and under water using a specialapparatus and tank. This method really provides an estimate of bodydensity.The various methods of determining body composition are describedin detail in textbooks of physiology or nutrition.Body composition is much influenced by nutrition. The two extremesare the wasting of nutritional marasmus and starvation and the overweightof obesity. Body composition differs between the genders and, perhapsonly slightly, among races. African Americans have been shown to haveheavier skeletons than whites of the same body build in the United States.In females pregnancy and lactation influence body composition.The body composition of children is influenced by their age andgrowth. Disturbances of growth resulting from nutritional deficienciesinfluence body composition, including the eventual size of the body andof body organs.Metabolism and EnergyThe general term for all the chemical processes carried out by thecells of the body is "metabolism". Chief among these processes is theoxidation (combustion, or burning) of food which produces energy. This