Determination of intravenous non-protein energy and nitrogen requirements in growing rats.
(65/2033)
Two experiments were conducted to estimate total non-protein energy and nitrogen requirements in growing healthy male Wistar rats nourished by parenteral nutrition. In experiment 1, non-protein energy varying from 30 to 70 kcal/day/rat were administered to animals receiving a constant dose of 80 mg nitrogen, plus vitamins and minerals. In experiment 2, nitrogen dosages varying from 0 to 280 mg N/day/rat with a constant dose of 60 kcal non-protein energy were studied. The formulation of the amino acid solution used in both experiments was based upon recommended oral amino acid requirements for growing rats. Dextrose served as the source of non-protein energy. Weight gain and nitrogen balance during a 6-day experimental period were used to determine requirements. Plasma free amino acids were also analyzed to evaluate the amino acid solution. Results indicate that under total parenteral nutrition conditions 578 to 621 mg/kg body weight3/4 nitrogen and 171 to 182 kcal/kg body weight3/4 non-protein energy are required to achieve growth of approximately 3 g/day. Inconsistent responses of plasma amino acid concentrations to the amounts infused were observed. It is suggested that the determined requirements can be applied as guidelines to research using the rat as an animal model in total parenteral nutrition. (+info)
Minimal enteral nutrient requirements for intestinal growth in neonatal piglets: how much is enough?
(66/2033)
BACKGROUND: Parenterally nourished preterm infants commonly receive minimal enteral feedings, the aim being to enhance intestinal function. Whether this regimen increases intestinal growth has not been established. OBJECTIVE: Our objective was to determine the minimal enteral nutrient intakes necessary to stimulate and to normalize neonatal intestinal growth. METHODS: Intestinal growth and cell proliferation were quantified in neonatal pigs given equal amounts of an elemental nutrient solution for 7 d. Different groups (n = 5-7 per group) received 0%, 10%, 20%, 40%, 60%, 80%, or 100% of total nutrient intake enterally, with the remainder given parenterally. RESULTS: In the jejunum, wet weight, protein mass, and villus height were significantly greater at enteral intakes >40%. Stimulation of ileal protein mass required a higher enteral intake (60%). In both segments, abrupt increases in DNA mass, crypt depth, ornithine decarboxylase activity, and crypt cells in S-phase occurred between enteral intakes of 40% and 60%. Circulating concentrations of glucagon-like peptide-2 and peptide YY, but not gastrin, increased significantly between enteral intakes of 40% and 60% and closely paralleled indexes of cell proliferation. CONCLUSIONS: The minimal enteral nutrient intake necessary to increase mucosal mass was 40% of total nutrient intake, whereas 60% enteral nutrition was necessary to sustain normal mucosal proliferation and growth. Our results imply that providing <40% of the total nutrient intake enterally does not have significant intestinal trophic effects. (+info)
Dietary arginine requirement of juvenile red drum (Sciaenops ocellatus) based on weight gain and feed efficiency.
(67/2033)
Increasing aquacultural production of red drum (Sciaenops ocellatus) has prompted the determination of many of this species' nutritional requirements. However, limited information is available concerning its amino acid requirements, especially for arginine. Therefore, a feeding trial was conducted with juvenile red drum to determine their quantitative dietary requirement for arginine. Experimental diets contained 35 g crude protein/100 g from red drum muscle and crystalline amino acids. Incremental levels of arginine were added to the diets in place of a mixture of glycine and aspartic acid to maintain all diets isonitrogenous. All diets were fed in triplicate to juvenile red drum for 7 wk. Graded levels of arginine significantly (P < 0.05) affected weight gain, feed efficiency, protein efficiency ratio (PER) and plasma arginine levels of the fish. Based on least-squares regression of feed efficiency and PER data, the minimum requirement (+/- SEM) of red drum for arginine was estimated at 1.44 (+/- 0.15) and 1.48 (+/- 0.12) g/100 g diet (4.11 and 4.23 g/100 g dietary protein), respectively. The arginine requirements estimated from weight gain data were 1.75 (+/- 0.18) g/100 g diet or 5.0 g/100 g dietary protein. These values are similar to those reported for other carnivorous fish species. (+info)
Dispensable and indispensable amino acids for humans.
(68/2033)
Here, we compared the traditional nutritional definition of the dispensable and indispensable amino acids for humans with categorizations based on amino acid metabolism and function. The three views lead to somewhat different interpretations. From a nutritional perspective, it is quite clear that some amino acids are absolute dietary necessities if normal growth is to be maintained. Even so, growth responses to deficiencies of dispensable amino acids can be found in the literature. From a strictly metabolic perspective, there are only three indispensable amino acids (lysine, threonine and tryptophan) and two dispensable amino acids (glutamate and serine). In addition, a consideration of in vivo amino acid metabolism leads to the definition of a third class of amino acids, termed conditionally essential, whose synthesis can be carried out by mammals but can be limited by a variety of factors. These factors include the dietary supply of the appropriate precursors and the maturity and health of the individual. From a functional perspective, all amino acids are essential, and an argument in favor of the idea of the critical importance of nonessential and conditionally essential amino acids to physiological function is developed. (+info)
Nitrogen and amino acid requirements: : the Massachusetts Institute of Technology amino acid requirement pattern.
(69/2033)
We review the current international recommendations concerning the protein (nitrogen) and amino acid requirements of healthy individuals, from infancy to the later years of adult life and describe the changes in the recommendations for protein that have been made, since those issued in 1985 by Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU), by the International Dietary Energy Consultative Group. The current international requirements for the specific indispensable amino acids are critiqued briefly, and the rationale and basis for the proposed Massachusetts Institute of Technology (MIT) amino acid requirement pattern are presented. The evidence is then summarized that supports its use in practical considerations of protein nutrition. It is suggested that this MIT amino acid requirement pattern provides the best current estimates of the minimum physiological requirements for the indispensable amino acids in children and adults. It is further concluded that it would be difficult to argue for the continued use of the amino acid requirement values proposed by FAO/WHO/UNU in 1985 in the planning and assessment of dietary protein intakes for population groups worldwide. The MIT amino acid requirement pattern supports and strengthens the relevance of dietary protein quality as an important factor in human protein and amino acid nutrition. (+info)
Contribution of microbial amino acids to amino acid homeostasis of the host.
(70/2033)
Among the reasons suggested for the discrepancy between N balance and tracer-derived indispensable amino acid (IAA) requirement estimates is the possibility that the metabolic requirement is met not only by the diet but also by IAA synthesized de novo by the gastrointestinal microflora, which are then absorbed. It is therefore crucial to better understand and quantify the microbial biosynthesis of amino acids in the human gastrointestinal tract and its potential role in providing IAA to meet human amino acid requirement. Here, the available evidence on the contribution of microbial amino acids to the host's amino acid homeostasis, applying the (15)N labeling paradigm, is summarized. Between 1 and 20% of circulating plasma lysine, urinary lysine and body protein lysine of the host, respectively, is derived from intestinal microbial sources and corresponds to a gross microbial lysine contribution of 11-68 mg. kg(-1). d(-1) in adult humans with an adequate protein intake when fecal or ileal microbial lysine enrichment is used as precursor. Factors affecting estimates of net microbial IAA contribution are discussed. It appears that the small intestine is responsible for a large part of microbial lysine uptake, although some absorption from the large intestine cannot be excluded. Nonoxidative lysine losses from the human gastrointestinal tract, which were found to be between 3.9 to 8.5 mg. kg(-1). d(-1), are necessary to estimate the net contribution of microbial IAA. It is reasonable to assume that microbial amino acid synthesis in the human gastrointestinal tract utilizes a mixture of various nitrogen sources, i.e., endogenous amino acids, urea and ammonia. Microbes in the small intestine may rely more on endogenous amino acids. Deprivation of nutrients, the intake of certain dietary nonstarch oligosaccharides, lipids, as well as protein intake level and source and level of consumption of certain amino acids can affect the composition and metabolic activity of the intestinal microflora and thus its fermentation products potentially available to the host. In conclusion, with the use of the (15)N labeling paradigm, a significant contribution of microbial lysine to the host lysine homeostasis is found. However, to assess the net contribution of microbial IAA and its importance in defining the adult IAA requirement, this is not the ultimately successful experimental strategy because the interpretation of results is complicated by the nitrogen recycling in the gut, the uncertainty of the precursor pool of absorption and the limited data on nonoxidative IAA losses from the human gastrointestinal tract. (+info)
The protein digestibility-corrected amino acid score.
(71/2033)
The protein digestibility-corrected amino acid score (PDCAAS) has been adopted by FAO/WHO as the preferred method for the measurement of the protein value in human nutrition. The method is based on comparison of the concentration of the first limiting essential amino acid in the test protein with the concentration of that amino acid in a reference (scoring) pattern. This scoring pattern is derived from the essential amino acid requirements of the preschool-age child. The chemical score obtained in this way is corrected for true fecal digestibility of the test protein. PDCAAS values higher than 100% are not accepted as such but are truncated to 100%. Although the principle of the PDCAAS method has been widely accepted, critical questions have been raised in the scientific community about a number of issues. These questions relate to 1) the validity of the preschool-age child amino acid requirement values, 2) the validity of correction for fecal instead of ileal digestibility and 3) the truncation of PDCAAS values to 100%. At the time of the adoption of the PDCAAS method, only a few studies had been performed on the amino acid requirements of the preschool-age child, and there is still a need for validation of the scoring pattern. Also, the scoring pattern does not include conditionally indispensable amino acids. These amino acids also contribute to the nutrition value of a protein. There is strong evidence that ileal, and not fecal, digestibility is the right parameter for correction of the amino acid score. The use of fecal digestibility overestimates the nutritional value of a protein, because amino acid nitrogen entering the colon is lost for protein synthesis in the body and is, at least in part, excreted in urine as ammonia. The truncation of PDCAAS values to 100% can be defended only for the limited number of situations in which the protein is to be used as the sole source of protein in the diet. For evaluation of the nutritional significance of proteins as part of mixed diets, the truncated value should not be used. In those cases, a more detailed evaluation of the contribution of the protein to the amino acid composition of the mixed diet is required. From such an evaluation, it appears that milk proteins are superior to plant proteins in cereal-based diets. (+info)
Dietary protein and nitrogen utilization.
(72/2033)
The first approach used to study the utilization of nitrogen in the body was based on the measurement of nitrogen balance. Limitations to this method reside in the difficulty of precisely determining nitrogen losses and, more specifically, miscellaneous N losses. These shortcomings are particularly restrictive when investigating adaptation of the organism to different levels of protein intake. The principal issue is to gain a better understanding of the adaptive processes that occur with high protein intakes and the possibility of producing a net protein accretion by nutritional means in different situations. The investigation of protein metabolism in relation to dietary proteins, with a focus on the postprandial phase of nitrogen diurnal cycling, enables a clearer determination of the metabolic pathways for dietary nitrogen as a function of different factors, which include the habitual protein level and intrinsic protein characteristics. We propose that this in vivo approach in humans should be used to validate simpler indices of the nutritional value of proteins. (+info)