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فرمت فایل word و قابل ویرایش و پرینت

تعداد صفحات: 79

Preface

This account of human nutrtion describes the basic facts in an clear andsimple way without the use of complicated details or much specialistlanguage. In the few places where more than this is necessary, elementaryexplanation are given. I believe that any averagely intelligent person willreadily gain a good knowledge of human nutrition from this book, which willalso be of value to students, teachers, nurses, doctors and healthprefessionals.

I would like to thank professors Anthony Angel and peter W. Andrews of theDepartment of Biomedical Scienc, University of shefiled, for the verygenerous facilities they provided during the several years it has taken to writethis book.Greald wiscman All the nenrgy needed for growth and repair of thebook. for ,usular activity of all kinds and for all the work done by cells comesfrom the metabolism of carbohydrate, fat, proten and alcohol. The numeriusother items of the diet, even though essenital for other reasons, do notprovide energy, although many are directly involved in the chemical reactionwhich vield enery (If the diet is adequate and properly balanced the energynormally comes chilfly from carbohydrate and fat, while most of the proteinis used for cell growth and repair. When there is not enough carbohydrateand fat, the protein is used for energy and is then not availabe for otherpurpoes. As dietary protein is generally less abundat than carbohydrate andfat and usually more expensive, using protein for energy is comparativelywastclit. In some communitics, however, there may be plentiful protein and itmay then be eaten in sufficient quantity to be used for both cell building andfor energy.

The intake of food is governed in health by the appetic which under ordinaryconditions controls the weitht of the body with remarkable precision. Manypeople taking only moderate care are able to keep their weight more or lessunchanged over several decades. If they take food in excess by only a smallamount, theat exvess energy can be disposed of as heat and thereby preventfat accumulation. This seems to work very efficiently in some people. It is,however, casy to over - ride the natural controlling mechanism and consumesubstantially more enery than is required. When this happens the excessenergy is stored in the body as fat.

During ageing there is a fall in the weight of the bones, due to loss ofminerals, plus a fall in the weight of the muscles, hence if the total bodywight remains constant there must be compensatory changes, mainly anincrease in the body fat.

Yhe ability of the body to override the mechanism which controls energyintake has survical value when the supply of food is unpredictable because itcnables fat to be accumulated when there is plenty of food and its energy tobe used later when food is scarce. How long a healthy adult can survicewithout food depends to a large extent on the fat stored: with adequatewater, prople have lived for many weeks. When people die during starvationthey often still have some fat in their body. They die because duringstarvation body protein is metabolised as well as body fat and it is the loss ofthe protein that is usually the cause of death.

Nutritional status

The nutriritional status of most people can be assecsed sufficiently well bytheir appearance, body weight and by simple questions about general health.For a more critical assesment their body mass index can be determined. Thisgives a witht for height ratio and is a good guide to underweight oroverweight in adults exvept for those who are extremely muscular or haveecessive accumulation of water in the body.

If weighting is not possible, an assessment can be made by measuring thecircumdrence of the upper arm with a tape - measure. A point midwaybetween the shoulder and the elbow is used with the arm at rest , preferablyhanging down. This simple measurement reflects the size of th3 underlying,uscles and the subcautaneous fat, as well as the bone and the skin. Inundernouished persons and in those overweight it will be the muscles and thefat which will change in bulk rather than the other tissues. For adult men ona satisfactory diet the circumference ranges from about 250-320 mm and forwomen from about 220-300 mm.

In children chronic energy lack causes a low height for age ratio, especially ifthe parents and siblings are of average height or more.

Energy content of food