Leucine Balance Research Articles

Postexercise Dietary Protein Ingestion Increases Whole-Body Leucine Balance in a Dose-Dependent Manner in Healthy Children

Postexercise Dietary Protein Ingestion Increases Whole-Body Leucine Balance in a Dose-Dependent Manner in Healthy Children

Endurance Exercise Attenuates Postprandial Whole-Body Leucine Balance in Trained Men.

Endurance exercise increases indices of small intestinal damage and leucine oxidation, which may attenuate dietary amino acid appearance and postprandial leucine balance during postexercise recovery. Therefore, the purpose of this study was to examine the effect of an acute bout of endurance exercise on postprandial leucine kinetics and net leucine balance. In a crossover design, seven trained young men (age = 25.6 ± 2.3 yr; V˙O2peak = 61.4 ± 2.9 mL·kg·min; mean ± SEM) received a primed constant infusion of L-[1-C]leucine before and after ingesting a mixed macronutrient meal containing 18 g whole egg protein intrinsically labeled with L-[5,5,5-H3]leucine, 17 g fat, and 60 g carbohydrate at rest and after 60 min of treadmill running at 70% V˙O2peak. Plasma intestinal fatty acid binding protein concentrations and leucine oxidation both increased (P < 0.01) to peaks that were ~2.5-fold above baseline values during exercise with a concomitant decrease (P < 0.01) in nonoxidative leucine disposal. Meal ingestion attenuated (P < 0.01) endogenous leucine rates of appearance at rest and after exercise. There were no differences (both, P > 0.05) in dietary leucine appearance rates or in the amount of dietary protein-derived leucine that appeared into circulation over the 5-h postprandial period at rest and after exercise (62% ± 2% and 63% ± 2%, respectively). Leucine balance over the 5-h postprandial period was positive (P < 0.01) in both conditions but was negative (P < 0.01) during the exercise trial after accounting for exercise-induced leucine oxidation. We demonstrate that endurance exercise does not modulate dietary leucine availability from a mixed meal but attenuates postprandial whole-body leucine balance in trained young men.

Consumption of whole eggs promotes greater stimulation of postexercise muscle protein synthesis than consumption of isonitrogenous amounts of egg whites in young men

Background: Protein in the diet is commonly ingested from whole foods that contain various macro- and micronutrients. However, the effect of consuming protein within its natural whole-food matrix on postprandial protein metabolism remains understudied in humans.Objective: We aimed to compare the whole-body and muscle protein metabolic responses after the consumption of whole eggs with egg whites during exercise recovery in young men.Design: In crossover trials, 10 resistance-trained men [aged 21 ± 1 y; 88 ± 3 kg; body fat: 16% ± 1% (means ± SEMs)] received primed continuous l-[ring-2H5]phenylalanine and l-[1-13C]leucine infusions and performed a single bout of resistance exercise. After exercise, participants consumed intrinsically l-[5,5,5-2H3]leucine-labeled whole eggs (18 g protein, 17 g fat) or egg whites (18 g protein, 0 g fat). Repeated blood and muscle biopsy samples were collected to assess whole-body leucine kinetics, intramuscular signaling, and myofibrillar protein synthesis.Results: Plasma appearance rates of protein-derived leucine were more rapid after the consumption of egg whites than after whole eggs (P = 0.01). Total plasma availability of leucine over the 300-min postprandial period was similar (P= 0.75) between the ingestion of whole eggs (68% ± 1%) and egg whites (66% ± 2%), with no difference in whole-body net leucine balance (P = 0.27). Both whole-egg and egg white conditions increased the phosphorylation of mammalian target of rapamycin complex 1, ribosomal protein S6 kinase 1, and eukaryotic translation initiation factor 4E-binding protein 1 during postexercise recovery (all P < 0.05). However, whole-egg ingestion increased the postexercise myofibrillar protein synthetic response to a greater extent than did the ingestion of egg whites (P= 0.04).Conclusions: We show that the ingestion of whole eggs immediately after resistance exercise resulted in greater stimulation of myofibrillar protein synthesis than did the ingestion of egg whites, despite being matched for protein content in young men. Our data indicate that the ingestion of nutrient- and protein-dense foods differentially stimulates muscle anabolism compared with protein-dense foods. This trial was registered at clinicaltrials.gov as NCT03117127.

Postexercise Dietary Protein Ingestion Increases Whole-Body Leucine Balance in a Dose-Dependent Manner in Healthy Children

Background: Protein ingestion is important in enhancing whole-body protein balance in children. The effect of discrete bolus protein ingestion on acute postexercise recovery has yet to be determined.Objective: This study determined the effect of increasing doses of ingested protein on postexercise whole-body leucine balance in healthy, active children.Methods: Thirty-five children (26 boys, 9 girls; age range: 9-13 y; weight mean ± SD: 44.9 ± 10.6 kg) underwent a 5-d adaptation diet (0.95 g protein ⋅ kg-1 ⋅ d-1) before performing 20 min of cycling 3 times with a concurrent, primed, constant infusion of [13C]leucine. After exercise, participants consumed an isoenergetic beverage (140 kcal) containing variable amounts of bovine skim-milk protein and carbohydrates (sucrose) (0, 5, 10, and 15 g protein made up with 35, 30, 25, and 20 g carbohydrates, respectively). Blood and breath samples were taken over the 3 h of recovery to determine non-steady state whole-body leucine oxidation (LeuOX) and net leucine balance (LeuBAL).Results: LeuOX (secondary outcome) peaked 60 min after beverage ingestion and demonstrated a relative dose-response over the 3 h of recovery (15 g = 10 > 5 > 0 g; P < 0.001). LeuBAL (primary outcome) demonstrated a dose-response over the 3 h [15 g (24.2 ± 8.2 mg/kg) > 10 g (11.6 ± 4.3 mg/kg) > 5 g (5.7 ± 1.9 mg/kg) > 0 g (-3.0 ± 1.7 mg/kg); all P < 0.01] with all conditions different from zero (all P < 0.001).Conclusions: Over the 3-h postexercise period, LeuBAL was negative with carbohydrate ingestion alone; however, the co-ingestion of carbohydrates and 5 g high-quality dietary protein was sufficient to promote a positive postexercise whole-body protein balance in healthy, active children. Moreover, LeuBAL increased in a dose-dependent manner within the protein range studied. Children should consider consuming a source of dietary protein after physical activity to enhance whole-body anabolism. This trial was registered at clinicaltrials.gov as NCT01598935.

Post‐Exercise Consumption of Whole Eggs or Egg Whites Improves Whole Body Leucine Balance but Does Not Differentially Modulate Leucine Kinetics in Resistance‐Trained Young Men

The consumption of isolated proteins and/or crystalline amino acids enhances the anabolic effect of resistance exercise during recovery. However, the effect of consuming dietary amino acids within their natural nutrient‐dense food matrix to support whole body recovery from resistance exercise has received little attention. Therefore, we determined the effects of whole egg versus egg white ingestion on whole body leucine metabolism in resistance‐trained young males. In crossover trials, six resistance‐trained men (21±1 y; 90±5 kg) received primed constant L‐[1‐13C]leucine infusions with repeated breath and blood samples collected before and 5 h after resistance exercise to determine whole body leucine endogenous rate of appearance (Endo Ra; estimate of protein breakdown), oxidation (OX), non‐oxidative leucine disposal (NOLD; estimate of protein synthesis) and net balance (NB). Immediately after resistance exercise, participants ingested intrinsically L‐[5,5,5‐2H3]leucine labeled whole eggs (18 g protein, 17 g fat; 1.6 g leucine) or egg whites (18 g protein, 0 g fat; 1.6 g leucine) in scrambled form. Endo Ra declined (P&lt;0.001) from fasting values after whole egg (15±1%) and egg white (22±3%) ingestion with no difference between conditions (P=0.14). Similarly, OX decreased over the 5 h period after whole egg and egg white ingestion (P&lt;0.001) with no differences between conditions (P=0.62). NOLD tended to increase (P=0.08) after ingestion of whole egg (10±2%) and egg white (6±3%) with no differences between conditions (P=0.17). As such, NB was negative before exercise but improved similarly (P&lt;0.001) after whole egg (97±6%) and egg white (102±9%) ingestion (P=0.36). In summary, there was a similar increase in whole body NB after the ingestion of whole eggs and egg whites, which was primarily modulated by changes in postprandial whole body protein breakdown rather than protein synthesis during post‐exercise recovery. These data demonstrate that consuming high‐quality protein within a complete food matrix is an effective nutritional strategy to improve whole body net protein balance after resistance exercise in trained young men.Support or Funding InformationVision 20/20 Grant, Division of Nutritional Sciences, University of Illinois at Urbana ‐ Champaign

Post-Exercise Protein Ingestion Increases Whole Body Leucine Balance in a Dose-Dependent Manner in Healthy Children

Post-Exercise Protein Ingestion Increases Whole Body Leucine Balance in a Dose-Dependent Manner in Healthy Children

Protein requirements and aging 1

Protein requirements and aging 1

“Fast proteins” with a unique essential amino acid content as an optimal nutrition in the elderly: Growing evidence

Adequate protein intake is crucial to maintain body protein content in elderly subjects, but quality of dietary proteins should be also considered since amino acid composition and rate of protein digestion modulate amino acid availability. This study investigates whether the efficacy of optimal protein intake levels for protein retention in the elderly is influenced by protein quality. We investigated the effect of a 10-day adequate-protein (AP) or high-protein (HP) diet together with the protein source as caseins (CAS) or soluble milk proteins (PRO) on whole-body (WB) protein synthesis (PS) and protein breakdown (PB) in 4 groups of healthy elderly men (mean ± SEM: 71.8 ± 24.4 yr). The study consisted of two periods of 4 h each: a post-absorptive period and a postprandial period. The fed state was defined by consumption every 20 min and for 4 h, of either 15 g or 30 g of PRO or CAS. Steady-state WB and splanchnic leucine kinetics were measured using a continuous infusion of L-[1-13C]leucine in the postabsorptive state and L-[1-13C]leucine infusion plus oral L-[5,5,5-2H3]leucine in the postprandial state. WB PS was stimulated by feeding only with HP diets, whereas WB PB corrected for splanchnic extraction showed a similar pattern of post-feeding decrease in all groups. Consequently, net leucine balance was greater in the postprandial state after HP meals than after AP meals, with PRO meals leading to a better postprandial leucine balance (3.63 ± 0.16 μmol kg FFM(-1) min(-1)vs. 2.77 ± 0.21 μmol kg FFM(-1) min(-1) for PRO HP and CAS HP, respectively; P = 0.005). Postprandial protein retention was better improved in elderly men by an increase in protein intake when the protein supplementation was provided as fast-digesting proteins that induce high leucine availability.

Moderate hyperglycemia and a blunted anabolic response to perioperative parenteral amino acids in type 2 diabetes mellitus patients undergoing colorectal cancer surgery

Insulin resistance of type 2 diabetes mellitus (T2DM) is accentuated by surgical stress. Hyperglycemia can also be exacerbated by nutrition support; so a balance of anabolic and euglycemic strategies is essential. Patients with T2DM (n=7) or without (ND, n=11) undergoing colorectal cancer surgery received parenteral nutrition (PN) based on 20% of resting energy expenditure as amino acids (AAs, from 20h preop). Glucose, protein kinetics and fractional synthesis rate (FSR) of hepatic secretory proteins were measured with D‐[6,6‐2H2] glucose, L‐[1‐13C]leucine and L‐[ring‐2H5]phenylalanine while fasting preop, and again while receiving PN two days postop. In fasted state preop, subjects were in negative leucine balance, with T2DM being more negative than ND (p&lt;0.027). PN improved leucine balance (p=0.008), but balance was more negative in T2DM. Surgery invoked an acute phase response with increased fibrinogen (p&lt;0.0001) and its FSR (p&lt;0.0007). Albumin FSR was maintained to a similar extent postop. Plasma glucose was similar preop, but higher postop in T2DM (p&lt;0.005), possibly resulting from a tendency for higher endogenous production (p&lt;0.10) and lower clearance (p&lt;0.13). Plasma AAs showed changes typical of surgery attenuated increases in branched chains (p=0.035) and essentials (p=0.026) in T2DM. PN with AAs supports acute phase response in T2DM but with moderate hyperglycemia and a blunted anabolic response. Higher AA doses or combined AA and low glucose are suggested achieve anabolic response in T2DM.(Canadian Institutes of Health Research)

The Anabolic Effect of Perioperative Nutrition Depends on the Patient's Catabolic State Before Surgery

We tested the hypothesis that the anabolic effect of hypocaloric, isonitrogenous nutrition in patients undergoing colorectal surgery depends on the patient's preoperative catabolic state. Although there is evidence to suggest that total parenteral nutrition more effectively spares protein in depleted than in nondepleted cancer patients, the influence of preoperative catabolism on the anabolic effects of hypocaloric nutrition in patients undergoing elective surgery is unknown. Seventeen patients undergoing colorectal surgery received intravenous infusion of glucose with amino acids. Feeding was administered over 72 hours, from 24 hours before until 48 hours after surgery. Glucose provided 50% of the patient's measured resting energy expenditure. Amino acids provided 20% of the resting energy expenditure. Whole-body leucine balance (difference between the incorporation of leucine into protein = protein synthesis and endogenous leucine release = proteolysis) was determined using L-[1-(13)C]leucine kinetics before and 2 days after surgery. We analyzed the association between the postoperative increase in leucine balance and the following factors: preoperative leucine balance, protein breakdown, weight loss, oxygen consumption, circulating concentrations of glucose, free fatty acids, insulin, glucagon, cortisol, albumin, age, duration of surgery, and blood loss. Of 6 potentially relevant variables, 4 (weight loss, protein breakdown, albumin, and cortisol) were removed because they were not significant during the stepwise linear regression procedure. Leucine balance and age were the remaining 2 factors that remained with the final regression model: Δleucine balance = 19.1 - (0.20 × age [years]) - (0.58) × leucine balance(preOP)). We demonstrate a significant association between the degree of preoperative catabolism, the patient's age, and the anabolic effect of hypocaloric nutrition (ClinicalTrials.gov registration ID: NCT01414946).

Age and sex affect protein metabolism at protein intakes that span the range of adequacy: comparison of leucine kinetics and nitrogen balance data

Research suggests that changes in leucine oxidation (leuox) with feeding may reflect adult protein requirements. We evaluated this possibility by assessing the effects of age, sex, and different protein intakes on whole-body leucine kinetics and nitrogen balance. Thirty-four young (n=18, 22–46 years) and old (n=16, 63–81 years) men and women completed three 18-day trials with protein intakes of 0.50, 0.75 and 1.00 g protein·kg body weight−1·d−1. Fasting and fed-state leucine kinetics were quantified on day 12 of each trial using a primed, constant infusion of L-[1-13C]leucine. Protein requirement was estimated using classical nitrogen balance measurements and calculations. Leucine kinetics parameters were influenced by age and sex across all protein intakes. With feeding, leuox increased more in old vs. young adults. Independent of age, fasting and fed-state leuox were lower, and net leucine balance (fasting+fed-state) was higher in women vs. men. Among all subjects and protein intakes, nitrogen balance was correlated with fed-state leuox (r=0.39), fed-state leucine balance (r=0.60), net leucine balance (r=0.49) and the change in leuox from the fasting to fed state (r=0.49) (P<.05 for all results). At the highest protein intake, the change in leuox with feeding was inversely correlated with protein requirement (r=−0.39). These findings indicate that leucine kinetics, especially leuox, reflect nitrogen balance-based estimates of the need for dietary protein and generally support the view that protein requirement is comparable between young and old adults.

Leucine balance, metabolic and satiety responses to a leucinerich meal in healthy elderly women

Many older adults experience a decline of appetite and may not meet their protein needs; a strategy to optimize protein retention is thus essential. Leucine has anabolic potential by stimulating protein synthesis via mRNA translation and insulin secretion. Postprandial responses to leucine‐rich versus isonitrogenous mixed meals were assessed in 9 healthy older women (70.1±2 y, BMI 23.7±2.7 kg/m2) by double‐blinded, randomized, crossover studies. Test meals provided 0.6 g protein and 16.0 kcal/kg LBM, once with added leucine (0.07 g/kg LBM), once without.ResultsFive‐hour whole‐body postprandial leucine oxidation response, measured by constant infusion of [1‐13C]leucine and enrichment of plasma 13C‐KIC and expired 13CO2 was further increased with meal+leucine. Yet, the resulting balance (intake‐oxidation) was greater (18.1±1.4 vs. without 11.3±1.3 mmol/5h, p&lt;0.001) suggesting more protein retention. Serum insulin and C‐peptide AUC were greater post meal+leucine, indicating more secretion. Plasma glucose excursions and free fatty acids suppression did not differ between meals. Addition of leucine had no effect on meal‐induced thermogenesis, satiety and gut peptide responses (GLP‐1, PYY 3–36, ghrelin). This study shows the anabolic potential of a leucine‐rich mixed meal in older women, a dietary strategy that may be used to promote protein anabolism without affecting appetite. (Funded by CIHR)

Does a reduced glucose intake prevent hyperglycemia in children early after cardiac surgery? a randomized controlled crossover study.

IntroductionHyperglycemia in children after cardiac surgery can be treated with intensive insulin therapy, but hypoglycemia is a potential serious side effect. The aim of this study was to investigate the effects of reducing glucose intake below standard intakes to prevent hyperglycemia, on blood glucose concentrations, glucose kinetics and protein catabolism in children after cardiac surgery with cardiopulmonary bypass (CPB).MethodsSubjects received a 4-hour low glucose (LG; 2.5 mg/kg per minute) and a 4-hour standard glucose (SG; 5.0 mg/kg per minute) infusion in a randomized blinded crossover setting. Simultaneously, an 8-hour stable isotope tracer protocol was conducted to determine glucose and leucine kinetics. Data are presented as mean ± SD or median (IQR); comparison was made by paired samples t test.ResultsEleven subjects (age 5.1 (20.2) months) were studied 9.5 ± 1.9 hours post-cardiac surgery. Blood glucose concentrations were lower during LG than SG (LG 7.3 ± 0.7 vs. SG 9.3 ± 1.8 mmol/L; P < 0.01), although the glycemic target (4.0-6.0 mmol/L) was not achieved. No hypoglycemic events occurred. Endogenous glucose production was higher during LG than SG (LG 2.9 ± 0.8 vs. SG 1.5 ± 1.1 mg/kg per minute; P = 0.02), due to increased glycogenolysis (LG 1.0 ± 0.6 vs. SG 0.0 ± 1.0 mg/kg per minute; P < 0.05). Leucine balance, indicating protein balance, was negative but not affected by glucose intake (LG -54.8 ± 14.6 vs. SG -58.8 ± 16.7 μmol/kg per hour; P = 0.57).ConclusionsCurrently recommended glucose intakes aggravated hyperglycemia in children early after cardiac surgery with CPB. Reduced glucose intake decreased blood glucose concentrations without causing hypoglycemia or affecting protein catabolism, but increased glycogenolysis.Trial registrationDutch trial register NTR2079.

A Protein–Leucine Supplement Increases Branched-Chain Amino Acid and Nitrogen Turnover But Not Performance

This study aimed to determine the effect of postexercise protein-leucine coingestion with CHO-lipid on subsequent high-intensity endurance performance and to investigate candidate mechanisms using stable isotope methods and metabolomics. In this double-blind, randomized, crossover study, 12 male cyclists ingested a leucine/protein/CHO/fat supplement (LEUPRO 7.5/20/89/22 g · h(-1), respectively) or isocaloric CHO/fat control (119/22 g · h(-1)) 1-3 h after exercise during a 6-d training block (intense intervals, recovery, repeated-sprint performance rides). Daily protein intake was clamped at 1.9 g · kg(-1) · d(-1) (LEUPRO) and 1.5 g · kg(-1) · d(-1) (control). Stable isotope infusions (1-(13)C-leucine and 6,6-(2)H2-glucose), mass spectrometry-based metabolomics, and nitrogen balance methods were used to determine the effects of LEUPRO on whole-body branched-chain amino acid (BCAA) and glucose metabolism and protein turnover. After exercise, LEUPRO increased BCAA levels in plasma (2.6-fold; 90% confidence limits = ×/÷ 1.1) and urine (2.8-fold; ×/÷ 1.2) and increased products of BCAA metabolism plasma acylcarnitine C5 (3.0-fold; ×/÷ 0.9) and urinary leucine (3.6-fold; ×/÷ 1.3) and β-aminoisobutyrate (3.4-fold; ×/÷ 1.4), indicating that ingesting ~10 g leucine per hour during recovery exceeds the capacity to metabolize BCAA. Furthermore, LEUPRO increased leucine oxidation (5.6-fold; ×/÷ 1.1) and nonoxidative disposal (4.8-fold; ×/÷ 1.1) and left leucine balance positive relative to control. With the exception of day 1 (LEUPRO = 17 ± 20 mg N · kg(-1), control = -90 ± 44 mg N · kg(-1)), subsequent (days 2-5) nitrogen balance was positive for both conditions (LEUPRO = 130 ± 110 mg N · kg(-1), control = 111 ± 86 mg N · kg(-1)). Compared with control feeding, LEUPRO lowered the serum creatine kinase concentration by 21%-25% (90% confidence limits = ± 14%), but the effect on sprint power was trivial (day 4 = 0.4% ± 1.0%, day 6 = -0.3% ± 1.0%). Postexercise protein-leucine supplementation saturates BCAA metabolism and attenuates tissue damage, but effects on subsequent intense endurance performance may be inconsequential under conditions of positive daily nitrogen balance.

Effects Of Leucine-Enriched Protein Supplementation On Subsequent Performance And Metabolism Following High-Intensity Cycling

Recently we observed that the addition of leucine with protein to high-carbohydrate recovery feeding ingested following intense cycling over 3 days led to a small enhancement in subsequent performance. It is also established that post-exercise protein feeding, both with and without added leucine, attenuates muscle damage and soreness, and can increase muscle-protein synthesis, but the metabolic consequences are largely unknown. PURPOSE: To investigate further putative mechanisms and the effects on metabolism of a post-exercise leucine-protein supplement and confirm a benefit to subsequent performance. METHODS: In a double-blind randomized crossover, 12 male cyclists ingested either a leucine/protein/carbohydrate/fat supplement (LEUPRO; respectively 7.5/20/89/22 g·h-1) or isocaloric carbohydrate/fat control (CON: 119/22 g·h-1) for 1-3 h post-exercise during a 6-day training block. Protein intake was clamped at 1.9 (LEUPRO) and 1.5 g·kg-1d∑-1 (CON). Using stable isotope methodology and LC-MS based metabolomics we determined the impact of LEUPRO on leucine turnover and amino acid metabolism. RESULTS: Following exercise, LEUPRO increased branch-chain amino acids (BCAA) in plasma (2.6-fold; 90%CL ×/÷1.1) and urine (2.8-fold; ×/÷1.2) and products of their metabolism: plasma acylcarnitine C5 (3.0-fold; ×/÷0.9) and urinary β-aminoisobutyrate (3.4-fold; ×/÷1.4). LEUPRO also increased whole-body leucine oxidation (5.6-fold; ×/÷1.1) and synthesis (4.8-fold; ×/÷1.1), and only with LEUPRO was recovery leucine balance (mean ± SD: 580 ± 215 μmol·kg-1h∑-1, control; -43 ± 24 μmol·kg-1h∑-1) and day-1 nitrogen balance (17 ± 20 mg·kg-1, control; -90 ± 44 mg·kg-1) positive. However, subsequent day 2-5 nitrogen balance was positive in CON (111 ± 86 mg·kg-1; LEUPRO: 130 ± 110 mg·kg-1). LEUPRO reduced serum creatine kinase by 21-25% (90%CL ±14%). Despite these effects, the impact of LEUPRO on sprint power was trivial (day 4: 0.4% ±1.0%; day 6: -0.3% ±1.0%). CONCLUSIONS: Despite saturation of post-exercise BCAA metabolism and apparent attenuated tissue damage, a leucine-protein supplement had a trivial effect on performance compared to control, possibly due to both treatment groups being in positive nitrogen balance. Supported by a grant from Nestec Ltd., Vevey, Switzerland.

The effect of oral leucine on protein metabolism in adolescents with type 1 diabetes mellitus.

Lack of insulin results in a catabolic state in subjects with insulin-dependent diabetes mellitus which is reversed by insulin treatment. Amino acid supply, especially branched chain amino acids such as leucine, enhances protein synthesis in both animal and human studies. This small study was undertaken to assess the acute effect of supplemental leucine on protein metabolism in adolescents with type 1 diabetes. L-[1-13C] Leucine was used to assess whole-body protein metabolism in six adolescent females (16–18 yrs) with type 1 diabetes during consumption of a basal diet (containing 58 μmoles leucine/kg/h) and the basal diet with supplemental leucine (232 μmoles leucine/kg/h). Net leucine balance was significantly higher with supplemental leucine (56.33 ± 12.13 μmoles leucine/kg body weight/hr) than with the basal diet (−11.7 ± −5.91, P < .001) due to reduced protein degradation (49.54 ± 18.80 μmoles leucine/kg body weight/hr) compared to the basal diet (109 ± 13.05, P < .001).

Effects of Chronic Metabolic Acidosis on Splanchnic Protein Turnover and Oxygen Consumption in Human Beings

Although metabolic acidosis stimulates protein catabolism, its effects on splanchnic protein turnover and energy expenditure have not been measured in human beings. We investigated the effects of chronic metabolic acidosis (CMA) on splanchnic protein dynamics and oxygen consumption in human beings by using a leucine tracer and mass-balance techniques. Five subjects were studied after 6 days of HCl-, CaCl(2)-, and NH(4)Cl-induced acidosis; 8 subjects served as controls. Blood samples were collected from the radial artery and the hepatic veins. Measurements were performed on plasma and whole-blood samples. Based on plasma measurements, subjects who had undergone CMA had lower rates of splanchnic proteolysis (-35%) and protein synthesis (-50%; P < .05) than controls, as well as a negative leucine kinetic balance (-6.81 +/- 2.48 micromol/kg/min/1.73 m(2) body surface [BS](-1)), compared with the neutral balance in control plasma samples (0.76 +/- 2.11 micromol/kg/min/1.73; P < .05 between groups). Based on measurements from whole blood, splanchnic proteolysis and protein synthesis did not differ significantly between CMA and control samples, and the net leucine kinetic balance was neutral in both groups (CMA, -0.69 +/- 1.57; controls, -0.74 +/- 3.45 micromol/kg/min/1.73). In CMA whole-blood measurements, splanchnic oxygen consumption (44.8 +/- 4.3 mL/min/1.73 m(2) BS) was slightly lower than in controls (57.5 +/- 8.4 mL/min/1.73 m(2) BS; P = NS). Splanchnic protein synthesis correlated with oxygen consumption (r = 0.82; P < .001). CMA reduces splanchnic protein turnover and results in a negative leucine balance--an effect that apparently is offset by the contribution of blood cells to organ leucine (and protein) dynamics. Protein synthesis is a major contributor (about 67%) to energy expenditure in splanchnic organs.

The effect of the source of nitrogen supplementation on nitrogen balance, rates of plasma leucine turnover, protein synthesis and degradation in sheep

Combined experiments of the isotope dilution method of [1-13C]leucine, open-circuit calorimetry and nitrogen (N) balance test were used to determine the effect of the source of N supplementation on N balance, whole body protein synthesis (WBPS) and degradation (WBPD) in sheep. The experiment was performed in a replicated 3 × 3 Latin square design. The control diet consisted of timothy hay, ground maize and soybean meal. The urea diet was the control diet supplemented with 1.5% urea. The SBM diet contained the same N and metabolisable energy as the urea diet, which was reached by changing ground maize and soybean meal weights of the control diet. Nitrogen retention was greater (p < 0.05) for the urea diet than the control and SBM diets. Plasma urea concentrations were highest for the SBM diet, followed by the urea diet, and the control diet was lowest. The WBPS and WBPD did not differ between diets, but were numerically lower for the urea and SBM diets. These results suggest that in sheep, urea supplementation influenced N retention without clear changes in WBPS and WBPD.

Stimulation of muscle anabolism by resistance exercise and ingestion of leucine plus protein

Leucine is known to stimulate muscle protein synthesis and anabolism. However, evidence for the efficacy of additional leucine to enhance the response of muscle anabolism to resistance exercise and protein ingestion is unclear. Thus, we investigated the response of net muscle protein balance to ingestion of additional leucine with protein in association with resistance exercise. Two groups of untrained subjects performed an intense bout of leg resistance exercise following ingestion of 1 of 2 drinks: flavored water (PL); or 16.6 g of whey protein + 3.4 g of leucine (W+L). Arteriovenous amino acid balance across the leg was measured to assess the anabolic response of muscle in each group. Arterial amino acid concentrations increased in response to ingestion of W+L. Amino acid concentrations peaked between 60 and 120 min after ingestion, and then declined to baseline values. Valine concentration decreased to levels significantly lower than baseline. Net balance of leucine, threonine, and phenylalanine did not change following PL ingestion, but increased and remained elevated above baseline for 90-120 min following W+L ingestion. Leucine (138 +/- 37 and -23 +/- 23 mg), phenylalanine (58 +/- 28 and -38 +/- 14 mg), and threonine (138 +/- 37 and -23 +/- 23 mg) uptake was greater for W+L than for PL over the 5.5 h following drink ingestion. Our results indicate that the whey protein plus leucine in healthy young volunteers results in an anabolic response in muscle that is not greater than the previously reported response to whey protein alone.

Effect of Insulin With Oral Nutrients on Whole-Body Protein Metabolism in Growing Pubertal Children With Type 1 Diabetes

Insulin treatment of children with insulin-dependent diabetes mellitus improves whole body protein balance. Our recent study, conducted in pubertal children with type 1 diabetes with provision of both insulin and amino acids, indicated a positive effect of insulin on protein balance, primarily through decreased protein degradation. The current study was undertaken to assess the effect of insulin on protein metabolism in adolescents with type 1 diabetes during oral provision of a complete diet. Whole-body protein metabolism in six pubertal children (13-17 y) with type 1 diabetes mellitus was assessed with L-[1-13C]leucine during a basal (insulin-withdrawn) period and during infusion of 0.15 U/kg/h regular insulin with hourly meals to meet protein and energy requirements. Net leucine balance was significantly higher with insulin and nutrients (13.1 +/- 6.3 micromol leucine/kg/h) than in the basal state (-21.4 +/- 2.8, p < 0.01) with protein degradation decreased from 138 +/- 5.6 mumol leucine/kg/h to 108 +/- 5.9 (p < 0.01) and no significant change in protein synthesis. Even with an ample supply of nutrients, insulin does not increase whole-body protein synthesis in pubertal children with type 1 diabetes mellitus and positive protein balance is solely due to a substantial reduction in the rate at which protein is degraded.