Branched-chain Amino Acids Requirement Research Articles

Serum Branched-chain Amino Acid Metabolites Increase When Aerobic Exercise Is Initiated With Low Muscle Glycogen

PURPOSE: Initiating aerobic exercise with low muscle glycogen blunts anabolic signaling and myogenesis. The underlying mechanisms causing the reduction in post-exercise anabolic signaling is unclear. This study aimed to identify metabolic factors that might contribute to the apparent muscle anabolic resistance that occurs when aerobic exercise is initiated with low muscle glycogen using global metabolomics. METHODS: Using a randomized, crossover design, 11 men (mean ± SD, age: 21 ± 4 y; VO2peak: 44 ± 4 mL/kg/min) completed 2 cycle ergometry glycogen depletion trials, followed by 24 hours of isocaloric high fat (1.5 g/kg carbohydrate, 3.0 g/kg fat) or high carbohydrate (6.0 g/kg carbohydrate, 1.0 g/kg fat) refeeding to elicit low (LOW; 217 ± 103 mmol/kg dry wt) or adequate (AD; 396 ± 70 mmol/kg dry wt) muscle glycogen content. Participants then performed 80 min of cycle ergometry (64 ± 3% VO2peak) and ingested 146 g of carbohydrate. Serum samples for metabolomics analysis were collected before glycogen depletion under resting, fasted conditions (BASELINE), before (PRE) and immediately after (POST) exercise. Changes in metabolite profiles were calculated by subtracting BASELINE from PRE and POST within LOW and AD. RESULTS: Treatment or time-by-treatment interactions were observed in 309 metabolites (P < 0.05, Q < 0.10), with 78% of identified metabolites being related amino acid or fatty acid metabolism. There were greater decreases in 80% of diacylglycerol metabolites, while 69% of acyl-carnitine metabolites had greater increases in LOW compared to AD (P < 0.05, Q < 0.10). There were greater increases in 64% of branched-chain amino acids (BCAA) metabolites, as well as urea and 3-methylhistidine in LOW compared to AD (P < 0.05, Q < 0.10). CONCLUSION: Greater increases in BCAA and acyl-carnitine metabolites, as well as urea and 3-methylhistidine, suggest that when aerobic exercise is initiated low muscle glycogen, the reliance on BCAA catabolism for substrate oxidation is greater than when exercise is initiated with adequate glycogen stores. Findings may provide a metabolic explanation for why muscle is anabolically resistant to the mechanical stimulus of exercise, and suggest exogenous BCAA requirements to optimize muscle recovery are likely increased when glycogen stores are limited.

Interactions of the branched-chain amino acids. 1. Influence of dietary isoleucine and leucine on the valine requirement of male Cobb MV × 500 broilers for a 29- to 42-day finisher period

Branched-chain amino acid requirements have traditionally been determined using dose-response titrations without accounting for the influence of branched-chain amino acid antagonism. As recent data has indicated that inherent levels of the non-tested amino acid may influence response curves in diets mimicking industry, these methods may result in over or under estimation of requirement values. Therefore, an experiment was conducted to determine if dietary levels of isoleucine and leucine influence 29 to 42 day valine needs through the implementation of a 5 × 2 × 2 factorial design. Twenty diets were fed to 7 replicate pens of 12 broilers. Body weight gain, feed intake, and FCR were determined for the 29 to 42 day period, and carcass traits were assessed on day 44. Valine × isoleucine and valine × leucine interactions were observed for BW gain and total breast yield ( P < 0.10). Body weight gain requirements ranged from 73 to 81 Val/Lys, whereas responses for total breast yield were generally negative. A 3 way interaction was observed for FCR in which requirements varied from 75 to 82 Val/Lys. These interactions indicate that formulation strategies based on previous data concerning valine or isoleucine may not produce the desired response in Cobb MV × 500 broilers and that the branched-chain amino acids should be considered as a whole and not individually.

Optimisation of branched-chain amino acid requirements for 15–21-day-old broiler chickens by using the Taguchi method

Context There are complex inter-relationships among the branched-chain amino acids (BCAAs), making the use of full factorial design experiments more complicated, costly and time-consuming when attempting to estimate the optimal levels of the BCAAs. Aims Two experiments were conducted to determine optimal concentrations of BCAAs by using the Taguchi method and mathematical models for broiler chickens during 15–21 days of age. Methods In the first experiment, the optimal concentrations of BCAAs were determined for broiler chickens, and the accuracy of the results was evaluated in the second experiment. The orthogonal array layout of L16 (43) was applied to test four concentrations of leucine (Leu), isoleucine (Ile) and valine (Val). To test the validity of the results from 16 diets selected by the Taguchi method and four additional diets from the full factorial design method, a total of 960 broiler chickens was assigned to these 20 experimental diets, with six replicates of eight birds each. The Taguchi method, the multi-objective genetic algorithm (MOGA) and the random search algorithm (RSA) were used to determine the best concentration of BCAAs on the basis of optimal bird performance, which was measured by bodyweight gain, feed intake, and feed conversion ratio (FCR). In the second experiment, six dietary treatments were formulated to establish the reliability of the predictions obtained from the first experiment (Experiment 1). Key results No exceptional concentrations of BCAAs were achieved for a maximum average daily gain and a minimum FCR; however, the diet containing 1.177–1.353% standardised ileal digestible (SID) Leu, 0.742–0.810% SID Ile, and 0.832–0.915% SID Val showed the best performance. The results of the second experiment indicated that the Taguchi method could be used instead of a full factorial design to optimise the amino acid requirements of broiler chickens. Conclusions The requirements of BCAAs were overestimated using the MOGA and RSA methods compared with the Taguchi method. Implications In commercial diets containing high levels of SID Leu, supplementation of an extra 5% SID Ile and Val may improve broiler performance during 15–21 days of age.

Serum Branched-Chain Amino Acid Metabolites Increase in Males When Aerobic Exercise Is Initiated with Low Muscle Glycogen

This study used global metabolomics to identify metabolic factors that might contribute to muscle anabolic resistance, which develops when aerobic exercise is initiated with low muscle glycogen using global metabolomics. Eleven men completed this randomized, crossover study, completing two cycle ergometry glycogen depletion trials, followed by 24 h of isocaloric refeeding to elicit low (LOW; 1.5 g/kg carbohydrate, 3.0 g/kg fat) or adequate (AD; 6.0 g/kg carbohydrate 1.0 g/kg fat) glycogen. Participants then performed 80 min of cycling (64 ± 3% VO2 peak) while ingesting 146 g carbohydrate. Serum was collected before glycogen depletion under resting and fasted conditions (BASELINE), and before (PRE) and after (POST) exercise. Changes in metabolite profiles were calculated by subtracting BASELINE from PRE and POST within LOW and AD. There were greater increases (p < 0.05, Q < 0.10) in 64% of branched-chain amino acids (BCAA) metabolites and 69% of acyl-carnitine metabolites in LOW compared to AD. Urea and 3-methylhistidine had greater increases (p < 0.05, Q < 0.10) in LOW compared to AD. Changes in metabolomics profiles indicate a greater reliance on BCAA catabolism for substrate oxidation when exercise is initiated with low glycogen stores. These findings provide a mechanistic explanation for anabolic resistance associated with low muscle glycogen, and suggest that exogenous BCAA requirements to optimize muscle recovery are likely greater than current recommendations.

Role of branched‐chain amino acids on growth, physiology and metabolism of different fish species: A review

Branched-chain amino acids (BCAAs), leucine, isoleucine and valine have an enormous functional significance because of their involvement in fish physiology. Branched-chain amino acids are not limited to act as substrates of protein synthesis but are also part of the protein synthesis regulation. BCAAs regulate various key signalling pathways. Leucine has a pivotal role in mTOR activation, while isoleucine and valine have a predominant energy and glucose metabolism action. Research over the years has highlighted the importance of dietary BCAAs levels on the growth and development of fish. The available data suggest that fish require slightly higher amounts of BCAAs at the initial stage than at the latter stages of life. BCAAs requirements of different fish species have indicated wide variations: 11.5 to 91.0 g leucine/kg dietary protein, 15.4 to 42.3 g isoleucine/kg dietary protein and 17.7 to 46.91 g valine/kg dietary protein. This review paper covers the dietary BCAA requirements of various fish species and the modulation action of BCAAs on vital functions, as protein synthesis, metabolic pathway, glucose transportation and immune response.

Branched-chain amino acid requirements for enterally fed term neonates in the first month of life

Knowledge of essential amino acid requirements in infants is important because excessive intake of protein can lead to increased long-term morbidity such as obesity. A deficient intake may lead to suboptimal growth and impaired neurodevelopment. The current recommended branched-chain amino acid requirements in infants aged 0-1 mo are based on the amino acid content of human milk. We quantified the requirements for isoleucine, leucine, and valine for term neonates by using the indicator amino acid oxidation method with [1-(13)C]phenylalanine as the indicator. Fully enterally fed term infants received randomly graded amounts of isoleucine (5-216 mg · kg(-1) · d(-1)), leucine (5-370 mg · kg(-1) · d(-1)), or valine (5-236 mg · kg(-1) · d(-1)) as part of an elemental formula. Data are expressed as means ± SDs. Eighty-three Asian, term neonates (mean ± SD birth weight: 3.3 ± 0.4 kg; gestational age: 39.4 ± 1.3 wk) were studied at a postnatal age of 13 ± 5 d. Mean requirements for isoleucine, leucine, and valine (measured in boys only) were 105 mg · kg(-1) · d(-1) (r(2) = 0.61, P < 0.001), 140 mg · kg(-1) · d(-1) (r(2) = 0.26, P < 0.01), and 110 mg · kg(-1) · d(-1) (r(2) = 0.35, P = 0.001), respectively. Current human milk-based recommendations for isoleucine and valine in term infants aged 0-1 mo are correct. However, the current recommendation for leucine (166 mg · kg(-1) · d(-1)) is higher than the mean requirement of 140 mg · kg(-1) · d(-1) that we determined in this study. This trial was registered at www.trialregister.nl as NTR1610.

148 Branched Chain Amino Acid Requirements for Term Neonates

Background: Dietary intake should meet the requirement to obtain an optimal growth and neurodevelopment in the neonate. The essential branched chain amino acids (BCAAs), leucine, isoleucine and valine, are mainly used for incorporation into body protein. Current recommended BCAA requirements for infants 0-6 months (respectively 156, 88 and 87 mg•kg−1•d−1, ratio 1.8:1:1) are based on the amino acid content of human milk. However, human milk fluctuates in composition during lactation and even during a feeding, while milk consumption rate varies widely as well. Questions remain on the validity to use mean amino acid composition of human milk to determine requirements. Objectives: To quantify the requirement of leucine, isoleucine and valine in term neonates using the Indicator Amino Acid Oxidation method. Design: Enterally fed term infants received randomly graded intakes of leucine (15-500 mg•kg−1•d−1), isoleucine (5-216 mg•kg−1•d−1) and valine (5-236 mg•kg−1•d−1). Breath samples containing 13CO2 were collected during L-[1-13C]phenylalanine (indicator amino acid) administration, measured by isotope ratio mass spectrometry and analysed using a biphasic regression crossover analysis. Results: 83 term Asian neonates (birth weight: 3.29 ± 0.4 kg, gestational age: 39.4 ± 1.3 wks, postnatal age: 12.6 ± 5.1 d) were included. The mean requirement (at breakpoint) for leucine, isoleucine and valine was respectively 140, 105 and 110 mg•kg−1•d−1 and the upper 95% confidence interval was 240, 152 and 165 mg•kg−1•d−1. Conclusion: The requirements of the individual BCAAs are almost twice the current recommendations. A Leu:lle:Val ratio of 1.3:1:1 is more appropriate in term formula.

14 Methionine Requirement in Presence of Cysteine in the Enterally Fed Term Neonate

Background: Experimental evidence of essential amino acid requirement in neonates is scanty. Recently, the branched chain amino acid requirements in term neonates were successfully determined using the indicator amino acid oxidation method. Methionine, an essential amino acid, can be used for protein synthesis, but serves as a precursor for homocysteine and cysteine as well. Current recommended total sulphur amino acid requirement for infants 0-1 months is 57 mg/kg/d (methionine 28, cysteine 29 mg/kg/d), which is based upon the content of human milk. Commercially available formulas provide a methionine intake of 45-80 mg/kg/d. Aim: To quantify the requirement of methionine in presence of cysteine (91 mg/kg/d) in term neonates using the Indicator Amino Acid Oxidation method. Methods: Fully enteral fed term infants received randomly graded intakes of methionine (3-59 mg/kg/d). Breath samples were collected for 13CO2 during L-[1-13C]phenylalanine (indicator amino acid) infusion, measured by isotope ratio mass spectrometry and analysed by applying a biphase regression crossover analysis. Results: Twenty-five neonates (birth weight 3.23 ± 0.31 kg, gestational age 38.9 ± 1.1 wks) were studied at a mean postnatal age of 13 ± 7 d. With increasing methionine intake, L-[1-13C] phenylalanine oxidation decreased (r = -0.83, p < 0.01). The mean requirement is determined at 38 mg/kg/d and the upper 95% confidence interval at 50 mg/kg/d (figure). Conclusion: Present recommendation for methionine requirement is too low, although most, but not all, formulas provide a population safe intake when 150 mL/kg/d is consumed.

Regulation of taste-active components of meat by dietary branched-chain amino acids; effects of branched-chain amino acid antagonism

1. The effects of dietary branched-chain amino acids (BCAAs) including leucine (Leu), isoleucine (Ile) and valine (Val) on taste-active components, especially free glutamate (Glu), in meat were investigated. 2. Broiler chickens (28 d old) were given varied dietary BCAA levels for 10 d before marketing. Dietary BCAA content ratios were either 100:100:100 (Low Leu group), 150:100:100 (Control group) or 150:150:150 (High Ile + Val group) for Leu:Ile:Val (% of each BCAA requirement according to NRC, 1994). Taste-related components of meat (free amino acids and ATP metabolites) and sensory scores of meat soup were estimated. 3. Free Glu content, the main taste-active component of meat, was significantly increased by dietary BCAA. Compared to the Control group, free Glu content increased by 30% in the High Ile + Val group. However, the inosine monophosphate (IMP) content in meat did not change among groups. 4. Sensory evaluation of meat soups showed that Control and High Ile + Val groups had different meat flavours. The sensory score of overall taste intensity was significantly higher in the High Ile + Val group. 5. These results suggest that dietary BCAA concentrations regulate free Glu in meat. Increasing dietary Ile + Val induces an increase in free Glu content of meat, improves meat taste and is more effective for increasing free Glu content in meat than decreasing dietary Leu level.

Effect of Orthotopic Liver Transplantation (OLT) on Branched-Chain Amino Acid Requirement

Little is known regarding the impact of liver transplantation on amino acid requirements in children. Since plasma levels of the branched-chain amino acids (BCAA) are decreased in the presence of normal levels of the aromatic amino acids after liver transplantation, normalization of hepatic function may not fully correct changes in BCAA metabolism that occur in the pretransplant period. The goal of the present study was to determine total BCAA requirements of children following liver transplantation. The requirement of total BCAA was determined using indicator amino acid oxidation (IAAO) in five clinically stable children (5.7 +/- 3.5 y, mean +/- SD) 1-8 y post liver transplantation. Children received in random order 6 graded intakes of total BCAA. Individual BCAA in the test diet were provided in the same proportions as present in egg protein to minimize the potential interactive effects of individual BCAA on assessment of requirement. Total BCAA requirement was determined by measuring the oxidation of L-[1-13C] phenylalanine to 13CO2 [F13CO2 in micromol/kg/h], after a primed, continuous infusion of the tracer and using a two-phase linear regression crossover regression analysis. The estimated average requirement and the upper limit of the 95% CI for total BCAA in children who have undergone liver transplantation were 172 and 206 mg/kg/d), respectively. Total BCAA requirement in children who have undergone orthotopic liver transplantation (OLT) remain increased in the post-liver transplant period when compared with healthy school aged children, but is decreased when compared with children with mild-moderate chronic cholestatic (MCC) liver disease.

Branched-Chain Amino Acid Needs in Children with Mild-to-Moderate Chronic Cholestatic Liver Disease ,

Protein-energy malnutrition is prevalent in children with chronic cholestatic liver disease. Supplementation of branched-chain amino acids (BCAA) in infants and children with chronic liver disease has been associated with significant improvement in growth and nitrogen balance, suggesting that BCAA requirements are increased in chronic liver disease. The goal of the present study was to determine the total BCAA requirement in children with mild-to-moderate chronic cholestatic (MCC) liver disease using indicator amino acid oxidation (IAAO). Total BCAA requirements were determined in 6 children (6.3 +/- 3.7 y, mean +/- SD) with MCC liver disease. Children were randomly assigned to receive 7 graded intakes of total BCAA. Individual BCAA in the test diet were provided in the same proportions as those present in egg protein to minimize the potential interactive effects of individual BCAA on assessment of requirement. The total BCAA requirement was determined by measuring the oxidation of l-[1-13C] Phe to 13CO2 [F13CO2 in micromol/(kg x h)], after a primed, continuous oral administration of the tracer and using a 2-phase linear regression crossover regression analysis. The estimated mean requirement and the upper limit of the 95% CI for total BCAA establishing using the IAAO in children with MCC liver disease were 209 and 272 mg/(kg x d), respectively. Total BCAA estimated average requirements using the IAAO were significantly higher than mean requirements established previously for healthy children (P < 0.05).

Branched-Chain Amino Acid Requirements in Healthy Adult Human Subjects1–4

There is now an expanding body of evidence to recommend, in the case of adult humans, the use of revised indispensable amino acid requirement values; these are approximately 2 to 3 times higher than the current international recommendations. The earlier methodologies for determining amino acid requirements, based on nitrogen balance, were criticized because of their design and the associated high energy intakes. The 1985 World Health Organization/Food & Agriculture Organization/United Nations University requirement for leucine has been demonstrated to be too low by short- and long-term (24-h) tracer-derived estimates of leucine oxidation and balance. The best values for leucine requirements come from 24-h direct amino acid oxidation (DAAO) and direct amino acid balance (DAAB) studies. Finally, we also collated all available data from studies on fed-state leucine oxidation with an adequate dietary adaptation period to assess the inflection on the leucine oxidation-leucine intake curve. The mean requirements for leucine, valine, and isoleucine are likely to be 40, 17-25, and 19 mg . kg(-1) . d(-1), respectively. This adds up to a total of approximately 84 mg . kg(-1) . d(-1), which is much lower than the lowest estimate of the total BCAA requirement of approximately 110 mg . kg(-1) . d(-1) made by the short-term indicator amino acid oxidation (IAAO) method, which determined the BCAA requirement from the pattern of oxidation of an indicator amino acid (phenylyalanine) at different levels of BCAA intake. An additional estimate of the leucine requirement was also made by a meta-analysis of all available 24-h DAAO/DAAB data from different studies. This resulted in a higher value for the leucine requirement than that obtained by the specific studies that utilized the 24-h DAAO/DAAB approach; however, even adding this value to the total BCAA requirement does not account for the difference in the total BCAA requirement estimates and the summed individual BCAA estimates.

Exercise Promotes BCAA Catabolism: Effects of BCAA Supplementation on Skeletal Muscle during Exercise

Branched-chain amino acids (BCAAs) are essential amino acids that can be oxidized in skeletal muscle. It is known that BCAA oxidation is promoted by exercise. The mechanism responsible for this phenomenon is attributed to activation of the branched-chain alpha-keto acid dehydrogenase (BCKDH) complex, which catalyzes the second-step reaction of the BCAA catabolic pathway and is the rate-limiting enzyme in the pathway. This enzyme complex is regulated by a phosphorylation-dephosphorylation cycle. The BCKDH kinase is responsible for inactivation of the complex by phosphorylation, and the activity of the kinase is inversely correlated with the activity state of the BCKDH complex, which suggests that the kinase is the primary regulator of the complex. We found recently that administration of ligands for peroxisome proliferator-activated receptor-alpha (PPARalpha) in rats caused activation of the hepatic BCKDH complex in association with a decrease in the kinase activity, which suggests that promotion of fatty acid oxidation upregulates the BCAA catabolism. Long-chain fatty acids are ligands for PPARalpha, and the fatty acid oxidation is promoted by several physiological conditions including exercise. These findings suggest that fatty acids may be one of the regulators of BCAA catabolism and that the BCAA requirement is increased by exercise. Furthermore, BCAA supplementation before and after exercise has beneficial effects for decreasing exercise-induced muscle damage and promoting muscle-protein synthesis; this suggests the possibility that BCAAs are a useful supplement in relation to exercise and sports.

Parenteral and Enteral Routes of Feeding in Neonatal Piglets Require Different Ratios of Branched-Chain Amino Acids

The requirements for total branched-chain amino acids (BCAA), isoleucine, leucine and valine, in neonatal piglets receiving parenteral and enteral nutrition was determined recently. The optimum ratio among BCAA during different routes of feeding is not yet known. In this study, the ratio of BCAA during parenteral and enteral feeding was tested using the indicator amino acid oxidation (IAAO) technique. Male Yorkshire piglets (n=24) received amino acid-based diets containing adequate nutrients for 5 d. Phenylalanine oxidation and kinetics were determined from a 4-h primed, constant infusion of L-[1-14C]-phenylalanine on d 6 and 8. On d 6, all piglets received a BCAA diet which met 75% of the total BCAA requirement, based on our previous research, with a ratio of 1:1.8:1.2 of isoleucine/leucine/valine. On d 8, the piglets were randomly assigned to receive one of the 3 test diets supplemented with isoleucine (+isoleucine), leucine (+leucine) or valine (+valine) to meet 100% of requirement, with the remaining two BCAA at 75% of requirement. The difference in phenylalanine oxidation (% of dose) between d 6 and 8 was used as an indicator of BCAA adequacy. In enterally fed piglets, the change in the percentage of the dose oxidized was minimal for all 3 test diets (mean=1.15%). In parenterally fed piglets, the difference in phenylalanine oxidation (% of dose) between d 6 and 8 was +isoleucine (12.6%), +leucine (2%) and +valine (6.6%). The ratio of 1:1.8:1.2 of isoleucine/leucine/valine is appropriate for enteral feeding, but during parenteral feeding, isoleucine was first limiting and valine was second limiting.

Effects of liver failure on the enzymes in the branched-chain amino acid catabolic pathway

Branched-chain α-keto acid dehydrogenase (BCKDH) complex catalyzes the committed step of the catabolism of branched-chain amino acids (BCAA). The liver cirrhosis chemically induced in rats raised the activity of hepatic BCKDH complex and decreased plasma BCAA and branched-chain α-keto acid concentrations, suggesting that the BCAA requirement is increased in liver cirrhosis. Since the effects of liver cirrhosis on the BCKDH complex in human liver are different from those in rat liver, further studies are needed to clarify the differences between rats and humans. In the valine catabolic pathway, crotonase and β-hydroxyisobutyryl-CoA hydrolase are very important to regulate the toxic concentration of mitochondrial methacrylyl-CoA, which occurs in the middle part of valine pathway and highly reacts with free thiol compounds. Both enzyme activities in human and rat livers are very high compared to that of BCKDH complex. It has been found that both enzyme activities in human livers were significantly reduced by liver cirrhosis and hepatocellular carcinoma, suggesting a decrease in the capability to dispose methacrylyl-CoA. The findings described here suggest that alterations in hepatic enzyme activities in the BCAA catabolism are associated with liver failure.

Branched-Chain Amino Acid Requirements in School-Aged Children Determined by Indicator Amino Acid Oxidation (IAAO)

The current WHO/FAO/UNU recommendations for BCAA requirements in school-aged children are based on nitrogen balance studies that have tended to produce lower estimates of amino acid requirements that those determined using stable isotope methodologies. The new dietary reference intake (DRI) recommendations for total BCAA requirements in children were determined using a factorial approach that included adult BCAA requirements plus the additional needs for growth. The purpose of this study was to determine directly total BCAA requirements in school children aged 6-10 y using indicator amino acid oxidation (IAAO). Five children (8.5 +/- 1.2 y) were assigned randomly to receive 7 graded intakes of total BCAA. Individual BCAA in the test diet were provided in the same proportions as those present in egg protein to minimize the potential interactive effects of individual BCAA on assessment of requirement. Total BCAA requirement was determined by measuring the oxidation of L-[1-13C] phenylalanine to 13CO2 [F13CO2 in micromol/(kg x h)], after a primed, continuous infusion of the labeled tracer and using a two-phase linear crossover regression analysis. The mean requirement and the population-safe intake level (upper limit of the 95% CI) of the total BCAA in healthy school aged children were 147 and 192 mg/(kg x d), respectively. The estimated mean requirements of the total BCAA as determined by IAAO is approximately 48% higher than the current DRI recommendations, suggesting that these recommendations may be too low to meet the needs of school-aged children.

Valine May Be the First Limiting Branched-Chain Amino Acid in Egg Protein in Men

Recently, we defined an estimate for total branched-chain amino acids (BCAA) using the indicator amino acid oxidation technique in men fed the three BCAA (leucine, isoleucine and valine) in the proportion present in egg protein. Although egg protein is regarded as a high quality dietary protein source, it is not known whether the proportions of the three BCAA are optimal. Five men with known total BCAA requirements were restudied. Each men was studied with isoleucine, leucine or valine held constant at that individual's requirement level while the intake of the other two BCAA was reduced; one BCAA was held constant and the intake of the other two was reduced by 10 and 20% in random order. The label appearance from the oxidation of L-[13C]-phenylalanine to 13CO2 (F13CO2) in breath was monitored in response to the change in amino acid intake. When either isoleucine or leucine was held constant, and the other two BCAA reduced by 20% (valine and leucine, or valine and isoleucine, respectively) F13CO2 increased (P = 0.007, P = 0.038, respectively). We conclude that valine may be the first limiting BCAA in egg protein.

The Total Branched-Chain Amino Acid Requirement in Young Healthy Adult Men Determined by Indicator Amino Acid Oxidation by Use of l-[1-13C]Phenylalanine

Previous recommendations for branched-chain amino acids (BCAA), based on nitrogen balance studies, were found to be low in a series of stable isotope-labeled amino acid studies. The BCAA requirement was increased in the new dietary reference intake (DRI) report on the basis of a series of stable isotope studies examining the requirement of leucine and valine individually, but not isoleucine. To reduce the possibility of interactions among these amino acids and imbalances in the mixture affecting the estimate of requirements, we decided to determine the requirement for the total BCAA of young healthy adult men, receiving a mixture of BCAA based on the proportion of these amino acids in egg protein, by use of indicator amino acid oxidation. Seven men were assigned to receive nine graded intakes of a BCAA mixture in random order: 34, 50, 66, 80, 100, 120, 140, 160 and 180 mg/(kg. d). The rate of release of (13)CO(2) from the oxidation of L-[1-(13)C]phenylalanine (F (13)CO(2)) was measured and a two-phase linear regression crossover model was applied to determine total BCAA requirement. The mean requirement and population-safe level (upper limit of 95% confidence interval) of the total BCAA were 144 and 210 mg/(kg. d), respectively. Based on the balance of BCAA in egg protein, our estimate for the mean leucine requirement is 55 mg/(kg. d), which is substantially higher than the 34 mg/(kg. d) recommended by the DRI.

The Branched-Chain Amino Acid Requirement of Parenterally Fed Neonatal Piglets Is Less than the Enteral Requirement

The requirements for branched-chain amino acids (BCAA), isoleucine, leucine and valine, in neonates have not been determined previously. Furthermore, the BCAA are considered to be catabolized primarily in the muscle and their metabolism in the small intestine has received little attention. In this study, the parenteral and enteral BCAA requirements were determined by the indicator amino acid oxidation (IAAO) technique. Male Yorkshire piglets (n = 32) received amino acid-based diets containing adequate nutrients for 5 d. On d 6 and 8, the piglets were randomly assigned to one of the test diets containing a fixed ratio of BCAA (1:1.8:1.2; isoleucine/leucine/valine). Diets were infused continuously via intravenous catheters for parenterally fed piglets or via gastric catheters for enterally fed piglets. Phenylalanine kinetics and oxidation were determined from a 4-h primed, constant infusion of L-[1-(14)C]phenylalanine. Phenylalanine oxidation (% of dose) decreased linearly (P < 0.05) as the BCAA intake increased from 0.2 to 1.53 g/(kg. d) and from 0.2 to 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively, after which the phenylalanine oxidation was low and the slope was not different from zero. Using breakpoint analysis, the mean total BCAA requirements were determined to be 1.53 and 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively. Thus, the parenteral requirement for total BCAA is 56% of the enteral requirement, suggesting that 44% of total BCAA is extracted by first-pass splanchnic metabolism.

Leucine, Isoleucine and Valine Requirements of Immature Beagle Dogs

Three experiments were conducted with growing beagle dogs fed crystalline L-amino acid diets, to determine the requirement for each of the branched-chain amino acids: leucine, isoleucine and valine. Requirements were taken as the minimum dietary concentrations required for optimal growth, feed efficiency and nitrogen retention. For each amino acid, the requirements estimated from each of these criteria were similar. Ten- to 12-week-old male beagle dogs were found to require 0.65% leucine, 0.40% isoleucine and 0.43% valine. These values correspond to 159 mg leucine, 98 mg isoleucine and 105 mg valine per 100 kcal dietary metabolizable energy. These branched-chain amino acid requirements of the growing dog are lower than those of weanling rats or pigs.