Protein nutrition nitrogen balance

Toxicity and Tacfcaging of Waste Nitrrigen Illustrated bv Experintental Nutrition Regulation of Protein Catabolism Nutritional Aspeets of Protein CaiabolUiti Nitrogen Balance C.rowth... 

Toxicity and Packaging of Waste Nitrogen Illustrated by Experimental Nutrition Regulation of Protein Catabolism Nutritional Aspects of Protein Catabolism Nitrogen Balance Growth... 

Not all proteins are nutritionally equivalent. Mote of some than of others is needed to maintain nittogen balance because different proteins contain different amounts of the various amino acids. The body s requirement is for specific amino acids in the correct proportions to replace the body proteins. The amino acids can be divided into two groups essential and nonessential. There are nine essential or indispensable amino acids, which cannot be synthesized in the body histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. If one of these is lacking or inadequate, then—regardless of the total intake of protein—it will not be possible to maintain nitrogen balance since there will not be enough of that amino acid for protein synthesis. 

O Parenteral nutrition (PN), also called total parenteral nutrition (TPN), is the intravenous administration of fluids, macronutrients, electrolytes, vitamins, and trace elements for the purpose of weight maintenance or gain, to preserve or replete lean body mass and visceral proteins, and to support anabolism and nitrogen balance when the oral/enteral route is not feasible or adequate. 

A number of procedures used to determine protein quality involve bioassays. Bioassays require feeding live animals protein ingredients for a specified period of time, and then estimating the nutritive value of the protein. Two such assays are the rat-based protein efficiency ratio (PER) bioassay and the human nitrogen balance assay (Dimes et al., 1994). Animal feeding experiments require chemical analyses of both the dietary inputs and then the metabolic output of the animal (e.g., body composition analysis, fecal sample analysis, collection, and assay for urine) from which the efficiency of protein metabolism can be predicted as well as how the protein supports animal growth and cell maintenance. 

The indication for administering BCAA in patients with hepatic encephalopathy to compensate amino-acid imbalance was proposed by J.E. Fischer et al. in 1974, and implemented parenterally. However, oral application of BCAA for an adequate treatment period also has beneficial effects on cirrhosis and HE (7.) improvement in protein tolerance and the nutritional condition, (2.) improvement in cerebral functions (II8, 122), probably due to an amelioration of liver function, (2.) stimulation of ammonia detoxification with a positive nitrogen balance (118), (4.) reduction in or normalization of AAA levels, and (5.) promotion of glutamine synthesis with a favourable effect on the cells of the immune system and on renal function. By means of BCAA, it was possible to prolong the survival time and delay the occurrence of liver failure in rats with CC -induced cirrhosis. (123, 126) However, there are diverging results, which need further clarification. In principle, the use of BCAA is considered to be a necessary form of supplementary treatment for catabolic metabolism in cirrhosis (124,125, 127, 128, 130-132), in (also latent) HE and after curative resection of hepatocellular carcinoma. (I2l) (s. p. 280)... 

The second half of this chapter concerns material of a less biochemical and a more nutritional nature. Three t5q es of protein nutrition are illustrated by studies with humans (1) the total fast, (2) the carbohydrate-only fast, and (3) a diet intended to maintain nitrogen balance. 

Nutritional Aspects of Protein Catabolism 449 TABLE 8.7 Nitrogen Balance Experiment... 

Major differences exist between the metabolic, fluid, and electrolyte management of patients with acute versus chronic kidney disease (CKD). For example, positive nitrogen balance is more difficult to achieve in patients with acute renal failure (ARF) due to the increased rate of protein catabolism. Additionally, patients with acute renal failure are more likely to develop hyperglycemia during nutritional support and frequently are dialyzed by modalities that are not used commonly for the patient with end-stage kidney disease (ESKD). Because of these differences, the nutritional management of patients with ARF is discussed separately. 

AMINO ACIDS On the market there are preparations containing 18 essential and non-essential amino-acids which are required for synthesis of the proteins of the body. The balance between the amino-acids is such that a positive nitrogen balance is obtained both in nutrition over long time periods and in the postoperative phase. In order that the amino-acids should be used optimally for protein synthesis, the need for energy should be supplied... 

Mohammed H. Rahman, Iqbal Hossain, and Moslehuddin, Nutritional evaluation of sweet lupin (Lupinus angustifolius) Net protein utilization (NPU) nitrogen balance and fractionation studies. Br. J. Nutr. 77(03) 443-157, March 1997. 

As can be expected, plasma proteins have a rapid turnover. Isotopic studies have shown that the half-life of a plasma protein molecule is about 15 days, and that plasma proteins are an important source of proteins in tissues. Animals put on a protein-free diet maintain a perfect nitrogen balance for 3 months when plasma is administered to them. During starvation, plasma proteins remain intact for a long time, in spite of rapid use of tissue proteins. These facts explain the salutary effects of plasma proteins administered for chronic malnutrition, or to surgical patients who cannot be fed. Since there is no correlation between the rate of plasma and tissue protein use in malnutrition, serum protein determination is of little value in estimating a patient s nutritional status. 

These studies show very clearly that it is not possible to draw any conclusions concerning the metabolic effects of a nutritive amino acid solution used in infants merely from nitrogen balance studies. The rate of protein synthesis rate during the period of artificial feeding might conceal possible disturbances of the synthesis of important structures or functions of certain organs, which for example are well known to us as secondary damage of an inborn error of the amino acid metabolism. 

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