Food and nutrition.pdf

Function of Food 85Metabolism of sodium and potassium, which are known aselectrolytes, is linked with body water. The sodium is mainly in theextracellular water and the potassium in the intracellular water. Most dietscontain adequate amounts of both these minerals. In fluid loss caused,for example, by diarrhoea or haemorrhage, the balance of electrolytes inthe blood may become disturbed. Water intake and electrolyte balanceare particularly important in sick infants. In healthy infants, breastmilkalone from a healthy mother provides adequate quantities of fluids andelectrolytes without additional water for the first six months of life evenin hot climates. Infants with diarrhoea and disease, however, may requireadditional fluids.While food intake is largely regulated by appetite and foodavailability, fluid intake is influenced by the sensation termed thirst. Thirstmay arise for various reasons. In dehydration it may be caused by dryingof the mouth but also by signals from the same satiety centre in thehypothalamus that controls hunger sensations. Dehydration, an importantfeature of diarrhoea.The phenomenon of water accumulation in the body is manifested inthe condition known as oedema, when disease causes an excess ofextracellular fluid. Two important deficiency diseases in which generalizedoedema is a feature are kwashiorkor and wet beriberi. The excess fluidmay result from electrolyte disturbances and accumulation of water inthe extracellular compartment. A person can have oedema and still bedehydrated from diarrhoea; this condition is a form of heart failure. Watercan also collect in the peritoneal cavity, in the condition known as ascites,which may be caused by liver disease.Body CompositionThe human body is sometimes said to be divided into threecompartments, accounting for the following shares of the total body weightof a well-nourished healthy adult male:• Body cell mass, 55 per cent.• Extracellular supporting tissue, 30 per cent.• Body fat, 15 per cent.The body cell mass is made up of cellular components such as muscle,body organs (viscera, liver, brain, etc.) and blood. It comprises the partsof the body that are involved in body metabolism, body functioning, bodywork and so on.The extracellular supporting tissue consists of two parts: theextracellular fluid (for example, the blood plasma supporting the bloodcells) and the skeleton and other supporting structures.Body fat is nearly all present beneath the skin (subcutaneous f~t) and