Leucine Balance Research Articles

Effects of 2-hydroxy-4-methylthiobutyrate on portal plasma flow and net portal appearance of amino acids in piglets

To determine whether portal plasma flow (PPF) and net portal appearance of amino acids (AA) could be affected by 2-hydroxy-4-methylthiobutyrate (HMB), six barrows (35-day-old, 8.6+/-1.4 kg), implanted with arterial, portal and mesenteric catheters, were fed a DL-methionine (as the control) or HMB-supplemented diet once hourly and infused intramesenterically with 1% p-amino hippurate. PPF was numerically 9% higher (P=0.09) in HMB-fed pigs than in controls over a 4-6 h period. Compared with controls, pigs fed the HMB diet had increased (P<0.05) net portal balance and/or appearance of leucine, isoleucine, histidine, arginine and alanine, but had decreased (P<0.05) portal appearance of glutamate over a 6-h period. The concentration of acetate in the lumen of the distal small intestine was higher (P=0.01) in HMB-fed pigs than in controls (25.14 vs. 7.64 mmol/kg). mRNA levels for proglucagon and endothelial nitric-oxide synthase (eNOS) in stomach and proximal small intestine, and mRNA levels for GLP-2 receptor (GLP-2R) in stomach were higher (P<0.05) in HMB-fed pigs compared with those in controls. Collectively, HMB supplementation increased concentrations of short-chain fatty acids in intestinal lumen, expression of proglucagon, GLP-2R, and eNOS genes, and net portal absorption of AA. These novel findings from the study with pigs may also have important implications for intestinal nutrition and health in humans.

Chemotherapy Does Not Influence Intestinal Amino Acid Uptake in Children

Chemotherapy will frequently induce intestinal damage (mucositis). Enteral nutrition is then often withheld for fear of impaired intestinal absorption as shown in animal models. There is no clinical evidence, however, that absorption is indeed compromised during chemotherapy-induced mucositis. The aim of this study was to evaluate systemic availability of dietary amino acids (leucine) during chemotherapy-induced mucositis. We studied eight childhood cancer patients (age 1.5-16 y) on 2 d, i.e. the day before chemotherapy and 3-5 d after. Chemotherapy-induced oral mucositis and diarrhea were scored on a World Health Organization toxicity scale. Stable isotope tracers were used to measure first-pass splanchnic leucine uptake and whole-body leucine kinetics. Patients showed increased mucositis and/or diarrhea toxicity scores (p < 0.0001) after chemotherapy. Systemic availability of enterally administered leucine was not significantly affected by chemotherapy (before 60%, after 90%, p = 0.46). Interestingly, five patients already showed a negative leucine balance before chemotherapy. In conclusion, most children receiving chemotherapy are already catabolic before start of a new cycle of chemotherapy. Amino acid transport as measured by leucine uptake in the intestine is not affected by chemotherapy-induced mucositis.

Postprandial whole-body protein metabolism after a meat meal is influenced by chewing efficiency in elderly subjects

Background: The rate of protein digestion affects protein utilization in elderly subjects. Although meat is a widely consumed protein source, little is known of its digestion rate and how it can be affected by the chewing capacity of elderly subjects.Objectives: We used a [1-13C]leucine balance with a single-meal protocol to assess the absorption rate of meat protein and to estimate the utilization of meat protein in elderly subjects with different chewing efficiency.Design: Twenty elderly volunteers aged 60–75 y were involved in the study. Ten of them had healthy natural dentition, and the other 10 were edentulous and wore complete dentures. Whole-body fluxes of leucine, before and after the meal (120 g beef meat), were measured with the use of a [1-13C]leucine intravenous infusion.Results: A rapid increase in plasma aminoacidemia and plasma leucine entry rate was observed after meat intake in dentate subjects. In complete denture wearers the increase in leucine entry rate was delayed (P < 0.05), and the amount of leucine appearing in peripheral blood during the whole postprandial period was lower than in dentate subjects (P < 0.01). Postprandial whole-body protein synthesis was lower in denture wearers than in dentate subjects (30% compared with 48% of leucine intake, respectively; P < 0.05).Conclusion: Meat proteins could be classified as fast digested proteins. However, this property depends on the chewing capacity of elderly subjects. This study showed that meat protein utilization for protein synthesis can be impaired by a decrease in the chewing efficiency of elderly subjects.

Parenteral sulfur amino acid requirements in septic infants

To investigate parenteral methionine requirements of critically ill, septic infants, we conducted an investigation involving 12 infants (age 2±1 years; weight 13±2kg) using the intravenous indicator amino acid oxidation and balance technique. They received a balanced parenteral amino acid formula supplying a cysteine intake at 36 mg.kg−1.d−1. They were randomized to one of 6 different methionine intakes. Total amino acid and energy intakes were 2±0.3g.kg−1.d−1 and 59±13 kcal/kg−1.d−1. After adaptation to the assigned methionine intake for at least 24 h, an L-[1-13C] leucine tracer was given as a primed, 6h continuous, intravenous infusion. As shown in the figure, leucine balance was negative at methionine intakes of 20 and 24 mg.kg−1.d−1 (p<0.05) and total sulfur amino acid (TSAA) intakes of 56 and 60 mg.kg−1.d−1. Leucine balance was positive at methionine intakes of 28, 35, 41 and 45 mg.kg−1.d−1, and TSAA intakes of 64, 71, 77 and 81 mg.kg−1.d−1. Methionine requirement of critically ill infants appears to be at least 27 mg.kg−1.d−1, at cysteine intakes of 36 mg.kg−1.d−1. Ajinomoto 3ARP Program. NIH DK 62363.

Similar 24h anabolic response to intact and hydrolysed whey protein ingested postexercise in elderly subjects

Since peptides are absorbed faster than intact proteins it was hypothesized that ingestion of protein hydrolysate after resistance exercise would cause a greater anabolic response than intact protein as timing is of significance in elderly. Muscle protein turnover was measured during a 27 h infusion of L-[1-13C]-leucine in 7 healthy (5M and 2F) aged 71(4) yr (mean(SEM)) who received on separate days carbohydrate with intact, IP or hydrolyzed whey protein, HP (0.25g/kg ~ 18g) over a 2h period after resistance exercise. Arteriovenous samples and muscle biopsies were obtained. Evaluated 1–1.5 h postexercise net balance of leucine was positive, although highest (p<0.05) in IP (0.38 ± 0.07 v 0.09 ± 0.08 mg*h−1*leg−1). Accordingly, was AUC of art-[leucine] higher in IP than HP (6.2 ± 0.5 v 5.4 ± 0.4 mmol/L). Subsequently, no difference was observed. Further, no differences were observed at any time point between IP and HP for protein synthesis, breakdown or oxidation. Muscle fractional synthetic rate was not different between IP an HP over 4 (0.07 ± 0.01 v 0.09 ± 0.01 %/h) or 24 hours post-exercise (0.08 ± 0.01 v 0.09 ± 0.01 %/h). These results suggest that protein ingested after resistance exercise in elderly results in a transient positive net protein synthesis, with no overall difference in the anabolic response between intact and hydrolysed whey.

The influence of sex on the protein anabolic response to insulin

We hypothesize that sex influences whole-body protein anabolism in the postabsorptive state and in response to hyperinsulinemia. Kinetics of 3- 3H-glucose and 13C-leucine were studied in 16 men and 15 women after energy- and protein-controlled diets, before and during a hyperinsulinemic, euglycemic, isoaminoacidemic clamp. In the postabsorptive state, women had 20% higher rates of leucine Ra (protein breakdown) and nonoxidative Rd (synthesis) adjusted for fat-free mass than men but net leucine balance was as negative. In response to hyperinsulinemia, leucine oxidation rates increased only in women and the change in net leucine balance was less than in men. Net leucine balance during the clamp correlated with rates of glucose disposal. Thus, women showed greater protein turnover rates when adjusted for fat free mass in the postabsorptive state, and lesser insulin sensitivity of protein anabolism and net protein accretion. A relationship exists between the protein anabolic response to insulin and the insulin sensitivity of glucose metabolism.

Whole body leucine flux in HIV-infected patients treated with or without protease inhibitors

The present study was carried out to assess the effects of protease inhibitor (PI) therapy on basal whole body protein metabolism and its response to acute amino acid-glucose infusion in 14 human immunodeficiency virus (HIV)-infected patients. Patients treated with PIs (PI+, 7 patients) or without PIs (PI-, 7 patients) were studied after an overnight fast during a 180-min basal period followed by a 140-min period of amino acid-glucose infusion. Protein metabolism was investigated by a primed constant infusion of l-[1-(13)C]leucine. Dual-energy X-ray absorptiometry for determination of fat-free mass (FFM) and body fat mass measured body composition. In the postabsorptive state, whole body leucine balance was 2.5 times (P < 0.05) less negative in the PI+ than in the PI- group. In HIV-infected patients treated with PIs, the oxidative leucine disposal during an acute amino acid-glucose infusion was lower (0.58 +/- 0.09 vs. 0.81 +/- 0.07 micromol x kg FFM(-1) x min(-1) using plasma [(13)C]leucine enrichment, P = 0.06; or 0.70 +/- 0.10 vs. 0.99 +/- 0.08 micromol x kg FFM(-1) x min(-1) using plasma [(13)C]ketoisocaproic acid enrichment, P = 0.04 in PI+ and PI- groups, respectively) than in patients treated without PIs. Consequently, whole body nonoxidative leucine disposal (an index of protein synthesis) and leucine balance (0.50 +/- 0.10 vs. 0.18 +/- 0.06 micromol x kg FFM x (-1) x min(-1) in PI+ and PI- groups respectively, P < 0.05) were significantly improved during amino acid-glucose infusion in patients treated with PIs. However, whereas the response of whole body protein anabolism to an amino acid-glucose infusion was increased in HIV-infected patients treated with PIs, any improvement in lean body mass was detected.

Whole-body protein anabolic response is resistant to the action of insulin in obese women

Background: Obesity is associated with insulin resistance of glucose and lipid metabolism. Objective: We sought to determine the effects of obesity on the insulin sensitivity of protein metabolism. Design: Whole-body [13C]leucine and [3H]glucose kinetics were measured in 9 lean and 10 obese women in the postabsorptive state and during a hyperinsulinemic, euglycemic, isoaminoacidemic clamp. Results: In the postabsorptive state, the leucine endogenous rate of appearance (catabolism), normalized for fat-free mass, was 11% greater and the nonoxidative rate of disappearance (synthesis) was 8% greater in the obese than in the lean women, but net balance was 29% more negative (P < 0.05). Clamp amino acid and glucose infusion rates were significantly lower in the obese women than in the lean women (0.65 ± 0.02 compared with 0.85 ± 0.04 and 5.7 ± 0.3 compared with 9.1 ± 0.5 mg · kg fat-free mass−1 · min−1, respectively; P < 0.0001 for both), and their rates correlated positively (r = 0.635, P = 0.005). During hyperinsulinemia, synthesis was stimulated less and net leucine balance was much lower in the obese women than in the lean women (−0.08 ± 0.06 and 0.30 ± 0.03 μmol · kg fat-free mass−1 · min−1, respectively; P < 0.0001). The percentage change in net leucine balance correlated negatively with all adiposity indexes. Plasma free fatty acids were less suppressed and the respiratory quotient was lower in the obese women than in the lean women. Conclusion: Obese women show a blunted protein anabolic response to hyperinsulinemia that is consistent with resistance to the action of insulin on protein concurrent with that on glucose and lipid metabolism.

Whole-body protein anabolic response is resistant to the action of insulin in obese women

Obesity is associated with insulin resistance of glucose and lipid metabolism. We sought to determine the effects of obesity on the insulin sensitivity of protein metabolism. Whole-body [(13)C]leucine and [(3)H]glucose kinetics were measured in 9 lean and 10 obese women in the postabsorptive state and during a hyperinsulinemic, euglycemic, isoaminoacidemic clamp. In the postabsorptive state, the leucine endogenous rate of appearance (catabolism), normalized for fat-free mass, was 11% greater and the nonoxidative rate of disappearance (synthesis) was 8% greater in the obese than in the lean women, but net balance was 29% more negative (P < 0.05). Clamp amino acid and glucose infusion rates were significantly lower in the obese women than in the lean women (0.65 +/- 0.02 compared with 0.85 +/- 0.04 and 5.7 +/- 0.3 compared with 9.1 +/- 0.5 mg x kg fat-free mass(-1) x min(-1), respectively; P < 0.0001 for both), and their rates correlated positively (r = 0.635, P = 0.005). During hyperinsulinemia, synthesis was stimulated less and net leucine balance was much lower in the obese women than in the lean women (-0.08 +/- 0.06 and 0.30 +/- 0.03 mumol x kg fat-free mass(-1) x min(-1), respectively; P < 0.0001). The percentage change in net leucine balance correlated negatively with all adiposity indexes. Plasma free fatty acids were less suppressed and the respiratory quotient was lower in the obese women than in the lean women. Obese women show a blunted protein anabolic response to hyperinsulinemia that is consistent with resistance to the action of insulin on protein concurrent with that on glucose and lipid metabolism.

Randomized clinical trial of the anabolic effect of hypocaloric parenteral nutrition after abdominal surgery

The observed failure of hypocaloric nutrition to establish an anabolic state after surgery may reflect inadequate control for the type and quality of analgesia in the studies performed. This study was designed to test the hypothesis that hypocaloric nutrition induces anabolism in patients who receive effective segmental pain relief using perioperative epidural analgesia. Sixteen patients who underwent colorectal surgery and received epidural analgesia were randomly assigned to receive intravenous glucose either without (glucose only) or with amino acids (nutrition). Feeding was administered over 48 h from surgical skin incision until the second day after operation. Glucose provided 50 per cent of the patient's resting energy expenditure (REE). Amino acids were infused at rates that provided 20 per cent of REE. Leucine rate of appearance (Ra), leucine oxidation and non-oxidative leucine disposal (NOLD) were assessed by measuring L-[1-13C]leucine kinetics. A positive leucine balance, that is the difference between NOLD and leucine Ra, indicated anabolism. After surgery, leucine Ra in the nutrition group was lower than that in the glucose only group (mean(s.d.) 88(25) versus 131(22) micromol per kg per h). The leucine balance remained negative in the glucose only group, whereas it became positive in the nutrition group (mean(s.d.) -24(3) versus 38(12) micromol per kg per h; P < 0.001). Patients who receive hypocaloric parenteral nutrition can be rendered anabolic after colorectal surgery in the presence of epidural analgesia.

Effect of Insulin with Concurrent Amino Acid Infusion on Protein Metabolism in Rapidly Growing Pubertal Children with Type 1 Diabetes

Insulin treatment of prepubertal children with insulin-dependent diabetes improves body protein balance by decreasing the rate of protein degradation without stimulating protein synthesis. However, insulin also causes hypoaminoacidemia, so the inability of insulin to stimulate protein synthesis may have been limited by substrate availability. We investigated the ability of insulin to stimulate protein synthesis in growing pubertal children who were given sufficient amino acids to counter insulin-induced hypoaminoacidemia. Protein metabolism in six pubertal children with type 1 diabetes was assessed from leucine kinetics during a primed, 6-h infusion of L-[1-(13)C]leucine. The children were studied in the postabsorptive state during a basal (insulin withdrawn) period and during the infusion of 0.83 mU * kg(-1) * min(-1) human regular insulin. Amino acids and glucose were given with insulin to prevent hypoaminoacidemia and hypoglycemia. Net leucine balance was significantly higher with insulin than in the basal state, the result of decreased protein degradation but also decreased protein synthesis. The data suggest that insulin alone does not increase protein synthesis in pubertal children with type 1 diabetes.

Response to lysine in a wheat gluten diet in adult minipigs after short-and long-term dietary adaptation as assessed with an indicator amino acid oxidation and balance technique1,2

An experiment was conducted to examine the response to wheat gluten (WG)-based diets at two lysine levels in adult minipigs (23 kg BW) using the indicator AA oxidation (IAAO) approach and N balance. Twenty minipigs (n = five per group), fitted with reentrant ileoileal cannulas allowing collection of ileal effluents, were fed restrictively two WG-based diets (WG and WG + Lys; 2.7 and 6.6 g of lysine/kg, respectively) for adaptation periods of 10 and 100 d. On d 7 and 9, for pigs fed the diets for 10 d, and on d 97 and 99, for pigs fed the diets for 100 d, primed i.v. fasted/fed tracer protocols with [(13)C]bicarbonate, and [(13)C]leucine were performed. With the WG diet, [(13)C]bicarbonate recoveries (%) were lower irrespective of the adaptation period, and higher during the fed period (fasted: WG + Lys = 82.5, and WG = 69.1; fed: WG + Lys = 90.6, and WG = 85.9; P < 0.05). Leucine oxidation rate was higher with the lower lysine intake (WG = 194.6 vs. 109.5 mg/[kg BW x d]; P < 0.05). Wheat gluten feeding resulted in a negative leucine balance independent of the adaptation period (WG = -29.1, and WG + Lys = 48.2 mg/[kg BW x d]; P < 0.05). In contrast with the IAAO method, N balance did not differ between the two lysine intakes, possibly because of an underestimation of N losses. The finding of a lower (13)C bicarbonate recovery with the lower dietary lysine intake suggests that caution should be taken in using a single recovery factor for all AA oxidation studies.

Daily requirement for total sulfur amino acids of chronically undernourished Indian men

Earlier studies of the requirement for total sulfur amino acids (SAAs; methionine in the absence of cystine) in healthy, well-nourished Indians indicated a value of 15 mg.kg(-1).d(-1), but it is unknown whether this estimate is applicable to chronically undernourished subjects. We assessed the total SAA requirement in otherwise clinically healthy, young, chronically undernourished adult Indians by using 7 test methionine intakes (3, 6, 9, 13, 18, 21, and 24 mg.kg(-1).d(-1)), without cystine, and by using both the 24-h indicator amino acid oxidation (24-h IAAO) and the 24-h indicator amino acid balance (24-h IAAB) methods. Twenty-one men were studied during each of 3 randomly assigned 7-d diet periods supplying methionine intakes (diet devoid of cystine) above and below the putative total 1985 FAO/WHO/UNU SAA requirement of 13 mg.kg(-1).d(-1). Twenty-four-hour IAAO and IAAB were measured on day 7 by use of a 24-h [(13)C]leucine tracer infusion. The breakpoint in the relation between these values and methionine intake was determined. Two-phase linear regression of daily leucine oxidation or the daily leucine balance against methionine intake estimated a breakpoint in the response curve at a methionine intake of 16 mg.kg(-1).d(-1) (95% Fiellers CI: 13, 22 mg.kg(-1).d(-1)). On the basis of the 24-h IAAO-IAAB approach, a mean total SAA requirement of 16 mg.kg(-1).d(-1) is proposed for undernourished Indian adults. This is not significantly different from that determined in Western and Indian well-nourished adults.

Kidney Protein Dynamics and Ammoniagenesis in Humans with Chronic Metabolic Acidosis

To evaluate the effects of chronic metabolic acidosis on protein dynamics and amino acid oxidation in the human kidney, a combination of organ isotopic ((14)C-leucine) and mass-balance techniques in 11 subjects with normal renal function undergoing venous catheterizations was used. Five of 11 studies were performed in the presence of metabolic acidosis. In subjects with normal acid-base balance, kidney protein degradation was 35% to 130% higher than protein synthesis, so net protein leucine balance was markedly negative. In acidemic subjects, kidney protein degradation was no different from protein synthesis and was significantly lower (P < 0.05) than in controls. Kidney leucine oxidation was similar in both groups. Urinary ammonia excretion and total ammonia production were 186% and 110% higher, respectively, and more of the ammonia that was produced was shifted into urine (82% versus 65% in acidemic subjects versus controls). In all studies, protein degradation and net protein balance across the kidney were inversely related to urinary ammonia excretion and to the partition of ammonia into urine, but not to total ammonia production, arterial pH, [HCO(-)(3)], urinary flow, the uptake of glutamine by the kidney, or the ammonia released into the renal veins. The data show that response of the human kidney to metabolic acidosis includes both changes in amino acid uptake and suppression of protein degradation. The latter effect, which is likely induced by the increase in ammonia excretion and partition into the urine, is potentially responsible for kidney hypertrophy.

Intestinal parasites increase the dietary lysine requirement in chronically undernourished Indian men

We previously used the 24-h indicator amino acid balance method to show that the lysine requirement in undernourished Indian men from low socioeconomic and unsanitary environments is approximately 50% higher than the mean requirement of 30 mg lysine. kg(-1). d(-1) in well-nourished men. It is possible that this higher lysine requirement in persons with chronic undernutrition is due to environmental influences, including the presence of intestinal parasites. We assessed this possibility by using 24-h indicator amino acid balance (with leucine) at both the "normal" requirement for lysine intake and the higher requirement, before and after successful treatment to eradicate intestinal parasites in affected, undernourished men. Fourteen chronically undernourished men were studied before and after treatment for intestinal parasites, during each of two 7-d (6-d dietary adaptation plus 1-d tracer experiment) diet periods supplying either 30 (n = 7) or 45 (n = 7) mg lysine. kg(-1). d(-1) from an L-amino acid diet. Twenty-four-hour indicator amino acid balance was estimated on day 6 by [(13)C]leucine tracer infusion. Before the parasite treatment, subjects were in neutral 24-h leucine balance at both lysine intakes. After the eradication of intestinal parasites, there was a significant (P < 0.001) improvement in 24-h leucine balances, which were positive at both lysine intakes. On the basis of the 24-h indicator amino acid balance approach, it appears that intestinal infestation with parasites increases the requirement for lysine and that this may be one factor responsible for the higher lysine requirement observed in persons with chronic undernutrition.

An adaptive metabolic demand model for protein and amino acid requirements.

The shortcomings of the metabolic implications of the current protein requirements model are reviewed, and an alternative model, validated with [1-(13)C]leucine balance results in human adults, is presented and evaluated in the context of defining protein requirements. The model identifies metabolic demands for amino acids as comprising a small fixed component and a variable adaptive component that is relatively insensitive to acute food or protein intake, but which changes slowly with a sustained change in intake, enabling N equilibrium to be achieved. The model accounts for the apparent low efficiency of utilisation of animal proteins in N balance studies and enables more realistic efficiency values to be measured within an experimental framework that takes account of the adaptive metabolic demand. However, the complex relationship between the adaptive metabolic demand and habitual level and quality of protein intake prevents prediction of protein quality by amino acid scoring, which can markedly underestimate actual values. In contrast to the current model, for fully adapted individuals risk of deficiency (i.e. negative N balance after complete adaptation) will only start to increase when intakes fall below the range of the true minimum requirements, i.e. a value that is currently unknown, but likely to be between 0.40 and 0.50 g/kg per d at the lower end of the reported distribution of requirements. At intakes greater than this with additional metabolic demands varying directly with intake, deficiency is only likely as a short-term response to a change to a lower intake within the adaptive range. Thus, for adults satisfying energy needs on most mixed human diets, intakes will be within the adaptive range, and N equilibrium ceases to be a useful indicator of nutritional adequacy of protein. In the context of prescriptive dietary guidelines it may be expedient to retain current values until the benefits (and any risks) of protein intakes within the adaptive range can be quantified. However, from a diagnostic perspective, indicators other than N balance need to be identified, since maintenance of N balance can no longer be used as a surrogate of adequate protein-related health.

The protein metabolic response to HIV infection in young children

Growth failure often precedes secondary infections in HIV-infected infants and children, suggesting that inadequate protein deposition may be an early manifestation of infection by the virus. However, the protein metabolic response elicited by the virus in young children is unknown. We compared children with HIV infection and age-matched children without HIV infection with regard to whole-body and splanchnic protein kinetics and synthesis of acute phase proteins (APPs). Whole-body and splanchnic leucine kinetics and fractional and absolute synthesis rates of 2 positive and 4 negative APPs were measured in 6 asymptomatic, HIV-infected children (4 males and 2 females) aged 6-17 mo and 4 uninfected children (3 females and 1 male) aged 7-9 mo who were in the fed state. Compared with the control children, the HIV-infected children had significantly lower dietary energy and protein intakes and leucine balance and significantly faster leucine flux and fractional splanchnic leucine extraction; there was no significant difference between the groups in leucine oxidation rates. The HIV-infected children also had significantly higher plasma concentrations and absolute synthesis rates of the positive APPs and a significantly higher fractional synthesis rate of fibrinogen. The concentrations of 2 of the 4 negative APPs, albumin and HDL apolipoprotein A-I, were significantly lower in the HIV-infected children but were not associated with slower synthesis rates. Children with HIV infection but without secondary infection have reduced protein balance because of an inability to down-regulate protein catabolism. Furthermore, the acute phase protein response elicited by HIV infection is characterized by higher concentrations and synthesis rates of positive APPs without lower concentrations of some negative APPs.

Leucine requirement and splanchnic uptake of leucine in chronically undernourished adult Indian subjects

We showed previously by the 24-h direct amino acid balance (DAAB) method that the leucine requirement of well-nourished Western and South Asian subjects is approximately 40 mg x kg(-1) x d(-1). It is not known whether this estimated leucine requirement is applicable in chronic undernutrition; therefore, we assessed the leucine requirement in Indian men with chronic, but stable, undernutrition. We studied 26 chronically undernourished men during 2 randomly assigned 7-d diet periods consisting of an L-amino acid diet (n = 20) and supplying either 14 and 30 (n = 10) or 22 and 40 (n = 10) mg leucine x kg(-1)x d(-1) or consisting of the subjects' habitual cereal-and-lentil-based diets (n = 6). The 24-h DAAB was estimated on day 6 by using a [13C]leucine tracer infusion. The splanchnic uptake of leucine was determined at an intake of 40 mg x kg(-1) x d(-1) by administering [2H3]leucine orally. By using mixed-models linear regression of leucine balance against leucine intake, we estimated a zero leucine balance at a leucine intake of 39.6 mg x kg(-1) x d(-1). The splanchnic first-pass uptake of [2H3]leucine was 22.7% and 11.5% of the intake in the fasted and fed phases, respectively. The subjects were in neutral leucine balance with their habitual cereal-and-lentil-based diets. On the basis of the 24-h DAAB approach, a mean leucine requirement of 40 mg x kg(-1) x d(-1) is proposed for healthy and for chronically undernourished Indian adults.

Lysine requirements of chronically undernourished adult Indian men, measured by a 24-h indicator amino acid oxidation and balance technique

In earlier studies with well-nourished subjects that used a 24-h indicator amino acid oxidation or balance approach, we concluded that the 1985 FAO/WHO/UNU requirement for lysine (12 mg x kg(-1) x d(-1)) was inadequate for healthy South Asian subjects and proposed a tentative requirement of 30 mg x kg(-1) x d(-1). We assessed whether chronic undernutrition, with low habitual dietary protein and lysine intakes, leads to changed lysine requirements. Twenty-seven otherwise clinically healthy, chronically undernourished Indian men were studied during 2 randomly assigned 7-d diet periods supplying 12 and 30, 18 and 36, or 24 and 42 mg lysine x kg(-1) x d(-1), based on an L-amino acid diet. The subjects' leucine intake was 40 mg x kg(-1) x d(-1). At 1800 on day 6, a 24-h intravenous [(13)C]leucine tracer-infusion protocol was conducted to assess leucine oxidation and daily leucine balance at each test lysine intake. A breakpoint was not identified in the lysine intake-leucine oxidation or balance response over the range of intakes studied. Mixed-models linear regression analysis indicated a mean requirement of 44 mg lysine x kg(-1) x d(-1) (95% CI: 36, 63) for the lysine intake-leucine balance relation. The mean lysine requirement in chronically undernourished men is estimated to be higher than the value of 30 mg x kg(-1) x d(-1) proposed for well-nourished individuals. This may be related to body-composition differences. It also suggests that these subjects have not elicited a metabolic adaptation in response to their habitually low lysine intakes by substantially improving their efficiency of dietary lysine utilization.

Efficiency of utilization of wheat and milk protein in healthy adults and apparent lysine requirements determined by a single-meal [1-13C]leucine balance protocol

We recently reported better wheat-protein utilization and a higher apparent lysine requirement than would be predicted, because of adaptive mechanisms of lysine conservation. However, such findings may be subject to the feeding protocol of frequent small meals. We used a [1-13C]leucine balance, large single-meal protocol to estimate the utilization of wheat and the consequent lysine requirements. Wheat and milk utilization were compared in 5 adults infused for 9 h with L-[1-13C]leucine, in the postabsorptive (0-3 h) and postprandial (3-9 h) states after ingestion of a single meal of either milk (30.4 kJ/kg; 32% of energy as protein) or a mixture of wheat gluten and whole wheat (29.2 kJ; 26.7% of energy as protein). Premeal nitrogen balance was predicted from [1-13C]leucine oxidation and postmeal balance predicted from cumulative increased leucine oxidation, enabling evaluation of the metabolic demand for protein, the efficiency of postprandial protein utilization (PPU), and the requirements for wheat protein and lysine. Mean (+/-SD) PPU was 0.61 +/- 0.03 and 0.93 +/- 0.02 for wheat and milk (P < or = 0.001), respectively, and the estimated average wheat-protein requirement (0.6 g.kg(-1).d(-1)/PPU) was 0.98 +/- 0.05 g.kg(-1).d(-1), indicating a lysine requirement of 18.3 +/- 1.0 mg. kg(-1).d(-1). Measured wheat utilization efficiency at 0.61 was considerably higher than the value predicted from wheat lysine intake and milk protein lysine deposition (ie, 0.222 +/- 0.004). These results confirm our previous finding that lysine conservation allows wheat protein to be utilized more efficiently than expected and is consistent with a lysine requirement in fully adapted individuals of 19 mg.kg(-1).d(-1), as indicated by recalculated nitrogen balance data.