Nitrogen balance method

Npkagawa, L, Takahashi, T, and Suzuki, T. (1961). Amino add requiremenis of children Minimal needs of lysine and methionine based on the nitrogen balance method.). N)dr. 

These shortcomings of the nitrogen balance method led us to attempt a supplementation of these data by measurements of the urinary amino acids and other metabolites. It is interesting to note that the urinary bound amino-N-output has been found to characterize the infant metabolism of various milk protein preparations more significantly than the N-retention values (36). This approach as will be discussed later has also afforded us a supplementary means of ascertaining the human requirements of tryptophan, lysine, and methionine and a measure of the dietary lack of amino acids, histidine and cystine, which fail to induce negative N-balance. 

The impact of physical activity on protein needs has been determined principally by using the nitrogen balance method. This approach requires measurements of nitrogen intake and losses (urine and feces) to determine individual protein requirements in response to stressors such as physical activity. A positive balance suggests protein accretion, whereas a negative balance suggests a net loss of body protein. 

De Datta SK, Trevitt ACF, Freney JR, Obcemea WN, Real JG, Simpson JR. 1989. Measuring nitrogen losses from lowland rice using bulk aerodynamic and nitrogen-15 balance methods. Soil Science Society of America Journal 53 1275-1281. 

Unsteady-State Mass Balance Method One widely used technique for determining Kj a in bubbling gas-liquid contactors is the physical absorption of oxygen or COj into water or aqueous solutions, or the desorption of such a gas from a solution into a sparging inert gas such as air or nitrogen. The time-dependent concentration of dissolved gas is followed by using a sensor (e.g., for O2 or CO2) with a sufficiently fast response to changes in concentration. 

Nielsen, K., Nielsen, L.P., and Rasmussen, P. (1995) Estuarine nitrogen retention independently estimated by the denitrification rate and mass balance methods a study of Norsminde Fjord, Denmark. Mar. Ecol. Prog. Ser. 119, 275-283. 

Nutritional sciences employ various experimental techniques. The methods used to assess a deficiency can also be used to determine the requirement for a given nutrient. Dietary deficiency, a technique applied to animals and microoigan isms, was used in the discovery of vitamins and in proving the essential nature of certain amino acids and lipids. This book features a strong emphasis on the techniques used to assess both requirements and deficiencies- Two of the most important techniques, those involving nitrogen balance and the respiratory quotient, are covered in some detail. 

The hydrogen and nitrogen balances support the higher air flow derived from the carbon balance, closing at 102 and 100% respectively by the indirect method. Sulfur and chlorine, present in the fuel in concentrations of 0.03 wt.%, were recovered at less than 60%. Both elements were present in fuel at concentrations close to the detection limits and closures were sensitive to small errors in analysis and material flows. A substantial fraction of chlorine remained in the gas phase past the cyclone at a stack exit temperature of 3S0°C. 

In this chapter we examine maintenance of nitrogen balance. This includes pathways and controls of nitrogen excretion as urea or ammonia. The method the body has for transferring nitrogen from one carbon skeleton to another is described. The metabolism of several amino acids, their physiological role, and their metabolic products are considered. Specific tissue metabolism and tissue-tissue interactions related to several amino acids are discussed. 

Since the true digestibility (the proportion of food nitrogen that is absorbed) is of crude protein is a reasonable approximation of the true digestibility of most amino acids (as determined by the rat balance method), it is recommended that amino acid scores be corrected only for the true digestibility of protein. 

Another method of determining protein requirements is the indicator amino acid oxidation technique. This method utilizes a carbon-labeled isotope (L-[1- C]) tracer that is ingested orally, and oxidation of this labeled carbon is measured in expired breath as COa. This method is based on the assumption that if one indispensable amino acid is dehcient, all other amino acids will be oxidized until that particular indispensable amino acid is available in adequate amounts, at which point oxidation of the amino acid pool, including the tracer, will be the lowest [32]. Using the indicator amino acid technique, researchers reported that protein recommendations are as much as 30 % higher than the WHO recommendations that are based on nitrogen balance studies [33]. The indicator amino acid oxidation method may help researchers reevaluate current protein requirements [34, 35]. 

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