Nutritive Value of Protein PDF

Protein Nitrogen balance  Nitrogen Balance i. A normal healthy adult is said to be in nitrogen balance, because dietary intake (I) equals daily loss through urine (U) feces (F) and skin (S). I=U+F+S  ii. Whenexcretion exceeds intake, it is negative nitrogen balance. iii. When intake ex...

Protein Nitrogen balance  Nitrogen Balance i. A normal healthy adult is said to be in nitrogen balance, because dietary intake (I) equals daily loss through urine (U) feces (F) and skin (S). I=U+F+S  ii. Whenexcretion exceeds intake, it is negative nitrogen balance. iii. When intake exceeds excretion, it is a state of positive nitrogen balance. iv. Nitrogen balance can be actually measured by calculating dietary intake of protein nitrogen (16% of weight of protein) and measuring daily excretion.  Factors Afectng Nitrogen Balance Growth: During period of active growth, a state of positive nitrogen balance exists. On an average when a person gains 5 kg, about 1 kg proteins are added to body. For this, about 160 g of nitrogen has to be retained, so he/she has to be in positive nitrogen balance. Hormones: Growth hormone, insulin and androgens promote positive nitrogen balance, while corticosteroids cause negative nitrogen balance. Convalescence: A person convalescing after an illness or surgery will be in positive nitrogen balance, due to active regeneration of tissues. Acute illness:  Negative nitrogen balance is seen in subjects immediately after surgery, trauma and burns. Chronic illness: Malignancy, uncontrolled diabetes mellitus and other debilitating diseases show negative nitrogen balance. Protein defciency: The defciency of even a single essential amino acid can cause negative nitrogen balance. Prolonged starvation is another important cause. Maintenance of Nitrogen Balance To maintain nitrogen balance, one has to satisfy need for nitrogen intake, which are: i. Obligatory nitrogen loss is 3.5 g of N/day for 65 kg person (urinary, fecal and cutaneous loss).  This could be equivalent to 22 g of protein. ii. Requirement for protein turnover. The minimum daily requirements to compensate for above two categories are 0.75-0.8 g/kg wt of good quality protein. iii. Protein requirements for growth. This is applicable in case of infants, children, adolescents, pregnancy, lactation and convalescence. As growth stops, protein requirement also decreases. Nutritve value of protein PER, BV digestibility coeficient, NPU values, PEPSIN digestibility  Assessment of Nutritonal Values Whipple introduced plasma pheresis as a means to assess nutritional value of proteins. Plasma from animal was taken, albumin was removed, rest of plasma was introduced back into the animal. The time for regeneration of original level of albumin in plasma was taken as a parameter of quality of the food given to animal. To assess nutritional value of a protein, is to give that protein as only source of nitrogen to an animal and assess weight gain. Biological Value (BV) of Protein  It is the ratio between amount of nitrogen retained and nitrogen absorbed during a specific interval. BV = Retained nitrogen × 100 Absorbed nitrogen Suppose 127 mg of a particular protein was consumed by a rat in a day and 4 mg is recovered in feces and 24 mg is seen in urine. Then Amount ingested = 127 mg Amount absorbed = 127 – 4 = 123 mg Amount retained = 123 – 24 = 99 mg Therefore BV = 99/123 × 100 = 81% Net Protein Utlizaton (NPU) NPU = retained nitrogen/intake of nitrogen × 100 In the above example, NPU of protein "A" = 99/127 × 100 = 78% and for protein "B", it is 4.5/100 × 100 = 4.5%. Thus NPU is a better index than BV to denote nutritional quality and availability of a protein. Net Dietary Protein Value (NDPV)  This will assess both quantity and quality of the proteins in the diet. NDPV = Intake of N × 6.25 × NPU Protein Efciency Rato or PER It is the weight gain per gram of protein taken. The essential amino acid content can also be expressed in terms of chemical score (mg of amino acid per gram of protein). By comparing chemical score of different proteins with egg protein which is taken as a reference protein, essential amino acid content can be assessed. Nutritive value of proteins (BV = biological value; NPU = net protein utilization; PER = protein efciency ratio) Fiber in foods and its role  Dietary fber consist of non-starch polysaccharides such as cellulose, arabinoxylons, insulin, pectin, mucilage, cellulose, chitins, hemicellulose, beta glucans and lignin. Non-starch polysaccharide is main components of dietary fber. Dietary fber comes from portion of plants that is not digested by enzymes in the intestinal tract. Part of it, however may be metabolized bacteria in lower gut. Diferent types of plants- have varying amounts and kinds of fber. There are two main types of fberr I. Water-soluble fibers: Pectin and gum are water-soluble fibers found inside plant cells. Beans, oat, bran, friuts and vegetable contain soluble fiber. They slow passage of food through intestines but do nothing to increase fecal bulk. II. Water insoluble fbers: These include cellulose, hemicellulose and lignin. They are metabolically inert and absorbs water as they move through digestive system. Such fbers increase fecal bulk and speed up passage of food through the digestive tract. Wheat bran and whole grains contain most insoluble fber, but skins of vegetables and beans also are good sources. They are present mostly in cell walls. Benefts of fberr I) Prevent constipation: Insoluble fber binds water, making stools softer and bulkier. Therefore, fber especially that found in whole grain products is helpful in treatment and prevention of constipation, hemorrhoids and diverticulosis.  Diverticula are pouches of the intestinal wall that can become infamed and painful. In past, a low-fber diet was prescribed for this condition. A high fber diet gives better results once infammation has subsided.  II. Lower carbohydrate digestion and absorption: Attract water and form viscous gel during digestion, slowing and emptying of stomach and intestinal tract and thus protect carbohydrates from digestive enzymes and delaying absorption of gucose. III. Lower cholesterol levels: Low blood cholesterol levels have been associated with a reduced risk of coronary heart disease. The body eliminates cholesterol through excretion of bile acids. Water-soluble fber binds bile acids, and hence a high-fber diet may result in an increased excretion of cholesterol.  Water soluble fber binds bile acids and hence a high fber diet may result in an increased excretion of cholesterol. Some types of fber appear to have a greater efect than others. The fber found in rolled oats is more efective in lowering blood cholesterol levels than the fber found in wheat. Pectin has a similar efect in that it, too, can lower amount of cholesterol in blood. IV) Reduce the risk of some cancers: Dietary fber may help reduce risk of some cancers, especially colon cancer. This idea is based on information that insoluble fber increases rate at which wastes are removed from body. This means body may have less exposure to toxic substances produced during digestion. A diet high in animal fat and protein also may play a role in development of colon cancer. V) Reducing weight: High-fber diets may be useful for people who wish to lose weight. Fiber itself has no calories, yet provides a "full" feeling because of its water-absorbing ability. For example, an apple is more flling than a half cup of apple juice that contains about the same calories. Foods high in fber often require more chewing, so a person is unable to eat a large number of calories in a short amount of time. Sources of Fiberr Dietary fber is found only in plant foods: fruits, vegetables, nuts and grains. Meat, milk and eggs do not contain fber. The form of food may or may not afect its fber content. Canned and frozen fruits and vegetables contain just as much fber as raw ones. Other types of processing, though, may reduce fber content.  Drying and crushing, for example, destroy water-holding qualities of fber. The removal of seeds, peels or hulls also reduces fber content. Whole tomatoes have more fber than peeled tomatoes, which have more than tomato juice. Likewise, whole wheat bread contains more fber than white bread. Adverse efectr  Although fber is important, it is just one part of a properly balanced diet.  Too much fber may reduce the amount of calcium, iron, zinc, copper and magnesium that is absorbed from foods. Defciencies of these nutrients could result if amount of fber in the diet is excessive, especially in young children.  Fiber supplements are sold in a variety of forms from bran tablets to purifed cellulose. Many laxatives sold as stool softeners actually are fber supplements. Fiber's role in diet is still being investigated. Various types of fber have diferent roles in the body. For these reasons fber supplements should be avoided. Eating a variety of fber-rich foods is best way to receive maximum benefts from each type of fber present in foods and obtain necessary nutrients. Thank you