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Daily L-Leucine Supplementation in Novice Trainees During a 12-Week Weight Training Program
Abstract
To investigate the effects of daily oral L-leucine ingestion on strength, bone mineral-free lean tissue mass (LTM) and fat mass (FM) of free living humans during a 12-wk resistance-training program.
Twenty-six initially untrained men (n = 13 per group) ingested either 4 g/d of L-leucine (leucine group: age 28.5 ± 8.2 y, body mass index 24.9 ± 4.2 kg/m2) or a corresponding amount of lactose (placebo group: age 28.2 ± 7.3 y, body mass index 24.9 ± 4.2 kg/m2). All participants trained under supervision twice per week following a prescribed resistance training program using eight standard exercise machines. Testing took place at baseline and at the end of the supplementation period. Strength on each exercise was assessed by five repetition maximum (5-RM), and body composition was assessed by dual energy X-ray absorptiometry (DXA).
The leucine group demonstrated significantly higher gains in total 5-RM strength (sum of 5-RM in eight exercises) and 5-RM strength in five out of the eight exercises (P < .05). The percentage total 5-RM strength gains were 40.8% (± 7.8) and 31.0% (± 4.6) for the leucine and placebo groups respectively. Significant differences did not exist between groups in either total percentage LTM gains or total percentage FM losses (LTM: 2.9% ± 2.5 vs 2.0% ± 2.1, FM: 1.6% ± 15.6 vs 1.1% ± 7.6).
These results suggest that 4 g/d of L-leucine supplementation may be used as a nutritional supplement to enhance strength performance during a 12-week resistance training program of initially untrained male participants.
... It has been suggested that daily supplementation with as little as 5 g of BCAAs can aid in the reduction of exercise-induced muscle damage (42). Although not including all BCAAs, it has further been reported that 12 weeks of resistance training in combination with as little as 4 g of leucine alone promotes significant strength increases in untrained men compared with consuming nothing (19). Lastly, caffeine and creatine are known to increase power output and volume of training in athletes and strength-trained populations (7,17,45,49). ...
... Individually, the aforementioned ingredients have been reported to mediate one or more of the following: (a) increases in serum testosterone levels (9,11), (b) enhancements of muscle size (43), and/or (c) enhancements of muscular strength (19). However, the combined effects of these ingredients have not been investigated despite the increasing popularity of MIPS. ...
... Because strength was significantly increased, this may confirm that the doses of BA in SUP suffice for young resistance-trained men, at least in combination with other ingredients in the current formulation. Leucine, one of the BCAAs, taken in 4 g$d 21 doses provided over 12 weeks in combination with a resistance training program was shown to increase strength compared with a lactose PL in untrained men (19). The range of daily BCAA consumption in the SUP was 2.5-5.0 g$d 21 (average, 3.75 g) of BCAAs, falling just short of the recommendations. ...
... Co-ingestion of LEU with a meal has been shown to improve MPS in older individuals (18,19). When provided as a daily supplement to healthy male participants in a resistance training intervention, there was a significant increase in strength and a nonsignificant increase in muscle mass versus placebo (20). Bukhari et al. (21) found that a daily-administered LEUenriched amino acid supplement at 3 grams/day stimulated MPS among older women, while another study utilizing LEU-enriched amino acid mixtures of approximately 3 and 6 grams/day in older men and women only found a significant increase in lean mass accretion at the higher dose (22). ...
... The 10-g daily dose of leucine utilized in our study was slightly higher than that used in studies that evaluated either lean mass accretion or stimulation of muscle protein anabolism without weight loss, ranging from 3-to 4-g per day provided in one dose (20,21). A weight loss study conducted by Verreijen et al. (24), utilizing a whey protein supplement containing 3 g of leucine, found that participants in the intervention group gained lean mass during weight loss (0.4 ± 1.2 kg) while those in the placebo group lost lean mass (0.5 ± 2.1 kg). ...
Objective:
This study evaluated the effect of leucine supplementation coupled with a calorie-restricted diet over a 12-week period in mid-life overweight and obese women on body composition and resting metabolic rate (RMR).
Method:
This study was a randomized, single-blind, placebo-controlled trial in which 34 women were randomly assigned to either 10 g leucine (LEU) or placebo daily, while following a calorie-restricted diet A dual energy x-ray absorptiometry (DXA) analysis, metabolic rate assessment via a BodyGem® and anthropometrics were performed at baseline and after the 12-week study to determine changes in fat mass, lean mass and RMR. Main variables were analyzed using 2 (condition) by 2 (time) mixed design ANOVAs with repeated measures. Odds ratio was calculated by counting the number of individuals gaining or maintaining lean mass (p ≤ .05).
Results:
Both groups lost a significant amount of weight due to both fat and lean mass loss, but there was no significant difference between groups, with RMR remaining unchanged over the course of the study and not significantly different between groups. The loss in lean mass was noticeably less, though not statistically significant (p = 0.644) for the women in the LEU group, with 38% vs. 6%, gaining or retaining lean mass during the intervention relative to the placebo.
Conclusions:
Our findings demonstrate that a greater proportion of mid-life overweight or obese women taking LEU supplements gained or maintained lean mass during intentional weight loss, though it did not reach a level of statistical significance.
... Katsanos et al. (23) evaluated the acute effects of leucine supplementation without exercise and reported that a higher level of leucine ingestion was needed among older versus younger adults to promote postprandial muscle protein synthesis (1.7 vs 2.8 g). In a 12-week RT plus leucine intervention, young male participants who consumed 4 g leucine daily and trained twice per week had significantly greater gains in strength compared to participants in the placebo group, as well as non-significant gains and losses in FFM and fat mass (FM), respectively (25). In an acute resistance exercise study in young males, investigators compared the anabolic response following resistance exercise with the administration of three different beverages (26). ...
... The 5-g daily dose of leucine utilized in our study is supported by other studies demonstrating the effectiveness of a similar dosage (16,18,20,24). The fact that we observed no significant increase in FFM with the 5-g daily dose of leucine supplementation is in contrast to studies of both young men and older men and women that utilized similar doses of leucine supplementation (25,27). Thus, the routine dietary intake and dosing protocol of the participants in the present study may have played a role. ...
Objective: This study investigated the effects of leucine supplementation with resistance training (RT) in untrained peri- and postmenopausal women on fat free mass, strength, and select anabolic-related hormones.
Method: This was a randomized, double-blind, placebo-controlled trial, in which 36 untrained women were randomly assigned to either a leucine or placebo supplement group coupled with 10 weeks of RT, performed thrice weekly, while ingesting either 5 g of placebo or leucine. Before and after RT, body composition and muscle strength were assessed and venous blood samples obtained to determine the levels of estradiol, testosterone, insulin-like growth factor-1, growth hormone, and cortisol. Data were analyzed by utilizing separate 2 × 2 [group × time (pretest and posttest)] factorial analyses of variance with repeated measures (p ≤ .05).
Results: There were no significant changes or differences between groups in fat free mass or with any of the serum hormones assessed in response to supplementation. However, there were significant increases in strength in both groups in response to RT, but not supplementation.
Conclusions: Peri- and postmenopausal women had significant increases in strength following 10 weeks of RT, with no additional effects from supplementing with leucine. There were no significant changes in either group regarding fat free mass or serum hormones.
... Leucine-rich EAAs exert stimulatory effects on skeletal muscle protein synthesis particularly via activation of the mammalian target of rapamycin (mTOR) signaling pathway and an inhibitory effect on proteolysis mediated by branched-chain keto acids [7][8][9]. Clinical studies showed that L-leucine supplementation enhanced strength performance during a resistance training program of initially untrained healthy subjects [10] and leucine supplementation improved muscle protein synthesis among elderly men [11]. In addition, enriching an EAA mixture with leucine demonstrated prophylaxis against age-related sarcopenia among the elderly [12]. ...
Background
Leucine, branched-chain amino acids (BCAA), represents an effective nutritional strategy to augment skeletal muscle mass in aging population. The study aimed to determine the effect of oral leucine-enriched BCAA supplementation on muscle mass, biomarkers of muscle synthesis and physical performance among elderly patients with chronic kidney disease (CKD).
Methods
A randomized controlled trial study was performed among patients with CKD stage III and IV aged over 65 year. Eligible participants were randomly assigned to either oral 4.5 g/day of leucine in mixed BCAA supplement (N = 29) or placebo (N = 26) in the same manner for 12 weeks. Blood chemistry, serum insulin growth factor-1 (IGF-1), serum myostatin, muscle mass using dual energy X-ray absorptiometry were measured at start and end of the intervention. Three-day food record was documented and reviewed by a dietitian. All participants were monitored for functional capacity using the handgrip and 6-minute walk tests during the study.
Results
Fifty-five patients (33 males) with mean age of 75.4 ± 5.2 years were enrolled. Daily protein and calorie intake during the study were similar in both groups. After the end of the study, lean muscle mass was significantly increased in the leucine group compared with that of the placebo group (0.4 kg (95% CI 0.1 to 0.7) vs. -0.2 kg; 95% CI -0.6 to 0.2) kg, P = 0.010, respectively). Also, statistically significant differences were noted in percentage of changed in muscle mass at 12 weeks between the leucine and placebo groups (1.0 ± 1.8 vs. -0.5 ± 2.6%, P = 0.014). However, muscle strength determined by handgrip and 6-minute walk tests, serum myostatin and IGF-1 did not significantly differ between the two groups. No serious adverse event was observed during the study.
Conclusions
In our study, 12 weeks of oral supplement with leucine-enriched BCAA resulted in increasing muscle mass, However, the treatment dose showed no benefit on biomarkers of muscle activity, functional capacity and adverse reaction among elderly patients with CKD.
... Further, greater increases in muscle strength were evident following WP plus LEU supplementation (compared to a maltodextrin placebo) in younger adults who underwent 8 weeks RET, suggesting supplementing with LEUenriched WP may have additional ergogenicity beyond that seen with RET alone [126]. Again, greater strength gains were evident after 12 weeks RET in conjunction with 4 g/day free-LEU supplementation in young untrained males [129]. Clinically significant gains in isometric leg strength were evident alongside moderate functional improvement during a timed-up-and-go test in healthy older adults when supplementing with a larger dose of free-LEU (10 g/day) alongside 12 weeks RET [130]. ...
Muscle protein synthesis (MPS) and muscle protein breakdown (MPB) are influenced through dietary protein intake and physical (in)activity, which it follows, regulate skeletal muscle (SKM) mass across the lifespan. Following consumption of dietary protein, the bio-availability of essential amino acids (EAA), and primarily leucine (LEU), drive a transient increase in MPS with an ensuing refractory period before the next MPS stimulation is possible (due to the "muscle full" state). At the same time, MPB is periodically constrained via reflex insulin actions. Layering exercise on top of protein intake increases the sensitivity of SKM to EAA, therefore extending the muscle full set-point (∼48 h), to permit long-term remodelling (e.g., hypertrophy). In contrast, ageing and physical inactivity are associated with a premature muscle full set-point in response to dietary protein/EAA and contractile activity. Of all the EAA, LEU is the most potent stimulator of the mechanistic target of rapamycin complex 1 (mTORC1)-signalling pathway, with the phosphorylation of mTORC1 substrates increasing ∼3-fold more than with all other EAA. Furthermore, maximal MPS stimulation is also achieved following low doses of LEU-enriched protein/EAA, negating the need for larger protein doses. As a result, LEU supplementation has been of long term interest to maximise muscle anabolism and subsequent net protein accretion, especially when in tandem with resistance exercise. This review highlights current knowledge vis-à-vis the anabolic effects of LEU supplementation in isolation, and in enriched protein/EAA sources (i.e., EAA and/or protein sources with added LEU), in the context of ageing, exercise and unloading states.
... L-Leucine can be used as a nutritional supplement to increase the strength performance during resistance training program (Ispoglou et al. 2011). The response of total muscle protein balance by ingestion of additional leucine with protein in association with resistance exercise was reported to be very beneficial. ...
... Na literatura pouco se fala sobre efeitos ergogênicos da Leucina nesse tipo de treinamento. Com o objetivo de analisar efeitos ergogênicos da Leucina sobre a massa magra e massa gorda, além do ganho de força em treinos de resistência, Ispoglou et al. [20] realizaram uma pesquisa com 26 homens saudáveis e destreinados. Os treinos de resistência eram de 5-RM e foram realizados durante 12 semanas, utilizando 8 máquinas de exercício padrão. ...
O interesse pela leucina vem crescendo cada vez mais por seu efeito ergogênico na promoção do anabolismo, envolvendo a síntese proteica e a degradação muscular. Por ser um aminoácido essencial, é de suma importância sua ingestão na dieta. A leucina desempenha três papéis importantes no nosso metabolismo: como substrato para a síntese proteica, como substrato energético e como sinalizador metabólico. O objetivo deste estudo foi avaliar o efeito da suplementação com leucina sobre a massa gorda. Participaram do estudo 24 jogadores de futebol profissionais da categoria sub 17 de um clube paulista pertencente a segunda divisão. Foram divididos em 2 grupos: 13 atletas foram suplementados com leucina e 11 com talco farmacêutico (placebo). Foram administradas 2 cápsulas antes do treinamento e 2 cápsulas após o treinamento contendo 0,5g de leucina cada cápsula, durante 25 dias. No momento inicial, foram aferidas e avaliadas as medidas antropométricas: peso, estatura, perímetro braquial, dobra subescapular e dobra tricipital que foram reavaliadas após 12 dias do início da suplementação e após o término dos 25 dias. Ao fim da pesquisa, observou-se que não houve alteração no percentual de gordura dos grupos em questão, com valores de, respectivamente, para os grupos placebo e suplemento de 15,92% ± 3,04; 17,74% ± 3,19. Não foram observados efeitos ergogênicos em relação ao desempenho físico, pois não foram realizados parâmetros de treinamento. Palavras chave: aminoácido, leucina, anabolismo, massa gorda, efeitos ergogênicos.Â
... Lean body mass and muscle power are also related to genetic control and growth factors such as hormone and hormone like compound that enhances the cells to produce gains in muscle fibre size. This may have caused variations in progress [12] . ...
The present study was conducted with an aim to investigate the effect of leucine supplementation in muscle growth of gym goers. 15 healthy male gym-goers ingested with 3 g/d of leucine and 15 healthy male gym goers were considered as test and placebo group, respectively. Their daily dietary intake was assessed and was told to stay on same diet and exercise routine till the completion of study period. Anthropometric measurements, body measurements and body composition were assessed on the initial day and at the end of the study period. A significant difference (p≤0.01) was observed between pre and post value of supplemented group for WHR. Medium effect size (0.7) for WHR between two groups was observed significantly which indicates that the change was moderate between the groups after supplementation. Independent t-test showed small value of effect size for visceral fat (0.3) and medium for bone mass (0.4) between two groups. These results states that 3 g/d of leucine supplementation for 45 days can enhance muscle growth and increases the strength performance of the gym persons.
Bu çalışmada amaç, voleybolda en çok kullanıldığı bildirilen besinsel destekler (C ve D vitamini, demir, magnezyum, kafein, sporcu ve enerji içecekleri, dallı zincirli aminoasitler, HMB, glutamin, whey, kreatin, bikarbonat, karnitin) hakkında bilgi vermektedir. Derlemenin içeriği, daha önce çok sayıda araştırmanın toplanıp yorumlandığı besinsel desteklerle ilgili derleme ve ilgili yayınların referans listeleri ile voleybolcular üzerinde yapılmış araştırma makaleleri özetlenerek oluşturulmuştur. İçeriğin hazırlanmasında derlemelerden yararlanılmasının nedeni, çok sayıda ve farklı sonuçlara ulaşan araştırma makalelerinin seçiminde ortaya çıkabilecek bireysel yanlılığı ortadan kaldırmaktır. Voleybolcular üzerindeki çalışma sayısının azlığı nedeniyle voleybolda besinsel destek (takviye/suplement) kullanımına özgü bilgi yetersiz olsa da, suplementler ile ilgili verilen bilgilerin okuyana fikir verecek yeterlilikte olduğu düşünülmektedir. Sonuç olarak, suplementlerin yararlarını araştıran çalışmalar yapılmaya devam etmektedir ve kullanım yanıtları yöntemsel ve bireysel farklılık gösterebilmektedir. Diğer takviyelerin vücutta eksikliği olmadığı sürece sporcuda sağlık veya performansı iyileştirmesi olası değildir. Hatta antrenmana daptasyonunu köreltmesi nedeniyle performansa, yaralanma riskini artırması nedeniyle de sağlığa zararlı etkileri olabilir.
Several dietary supplements have been proposed as a means of improving muscle strength and hypertrophy when combined with resistance training. However, few have received sufficient attention from sports scientists to produce robust evidence for being well recommended. A growing body of literature has emerged for several dietary ingredients with the potential to promote muscular adaptations. Therefore, the aim of this review is to provide an evidence-based review of the efficacy of emerging nutritional supplements to allow athletes, coaches, and practitioners to make an informed decision when considering their use as a means of improving muscle strength and hypertrophy.
Cancer cachexia induces host protein wastage but the mechanisms are poorly understood. Branched-chain amino acids play a regulatory role in the modulation of both protein synthesis and degradation in host tissues. Leucine, an important amino acid in skeletal muscle, is higher oxidized in tumor-bearing animals. A leucine-supplemented diet was used to analyze the effects of Walker 256 tumor growth on body composition in young weanling Wistar rats divided into two main dietary groups: normal diet (N, 18% protein) and leucine-rich diet (L, 15% protein plus 3% leucine), which were further subdivided into control (N or L) or tumor-bearing (W or LW) subgroups. After 12 days, the animals were sacrificed and their carcass analyzed. The tumor-bearing groups showed a decrease in body weight and fat content. Lean carcass mass was lower in the W and LW groups (W = 19.9 0.6, LW = 23.1 1.0 g vs N = 29.4 1.3, L = 28.1 1.9 g, P < 0.05). Tumor weight was similar in both tumor-bearing groups fed either diet. Western blot analysis showed that myosin protein content in gastrocnemius muscle was reduced in tumor-bearing animals (W = 0.234 0.033 vs LW = 0.598 0.036, N = 0.623 0.062, L = 0.697 0.065 arbitrary intensity, P < 0.05). Despite accelerated tumor growth, LW animals exhibited a smaller reduction in lean carcass mass and muscle myosin maintenance, suggesting that excess leucine in the diet could counteract, at least in part, the high host protein wasting in weanling tumor-bearing rats.
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 16.6g of whey protein+ 3.4g 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 120min 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 90120min following W+L ingestion. Leucine (138 37 and23 23mg), phenylalanine (58 28 and38 14mg), and threonine (138 37 and23 23mg) uptake was greater for W+L than for PL over the 5.5h 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.
Amino acids stimulate protein synthesis in skeletal muscle by accelerating translation initiation. In the two studies described herein, we examined mechanisms by which amino acids regulate translation initiation in perfused skeletal muscle hindlimb preparation of rats. In the first study, the effects of supraphysiological amino acid concentrations on eukaryotic initiation factors (eIF) 2B and 4E were compared with physiological concentrations of amino acids. Amino acid supplementation stimulated protein synthesis twofold. No changes were observed in eIF2B activity, in the amount of eIF4E associated with the eIF4E-binding protein (4E-BP1), or in the phosphorylation of 4E-BP1. The abundance of eIF4E bound to eIF4G and the extent of phosphorylation of eIF4E were increased by 800 and 20%, respectively. In the second study, we examined the effect of removing leucine on translation initiation when all other amino acids were maintained at supraphysiological concentrations. Removal of leucine from the perfusate decreased the rate of protein synthesis by 40%. The inhibition of protein synthesis was associated with a 40% decrease in eIF2B activity and an 80% fall in the abundance of eIF4E.eIF4G complex. The fall in eIF4G binding to eIF4E was associated with increased 4E-BP1 bound to eIF4E and a reduced phosphorylation of 4E-BP1. In contrast, the extent of phosphorylation of eIF4E was unaffected. We conclude that formation of the active eIF4E.eIF4G complex controls protein synthesis in skeletal muscle when the amino acid concentration is above the physiological range, whereas removal of leucine reduces protein synthesis through changes in both eIF2B and eIF4E.
HURLEY, B. F., J. M. HAGBERG, A. P. GOLDBERG, D. R. SEALS, A. A. EHSANI, R. E. BRENNAN, and J. O. HOLLOSZY. Resistive training can reduce coronary risk factors without altering [latin capital V with dot above]O2max or percent body fat. Med. Sci. Sports Exerc., Vol. 20, No. 2, pp. 150-154, 1988. Eleven healthy, untrained males (age = 44 +/- 1 yr, range = 40 to 55 yr) were studied to determine the effects of 16 wk of high-intensity resistive training on risk factors for coronary artery disease. Lipoprotein-lipid profiles, plasma glucose and insulin responses during an oral glucose tolerance test, and blood pressure at rest were determined before and after training. The training program resulted in a 13% increase in high-density lipoprotein-cholesterol (39 +/- 2 vs 44 +/- 3 mg [middle dot] dl-1, P < 0.05), a 43% increase in high-density lipoprotein-cholesterol2 (7 +/- 2 vs 10 +/- 2 mg [middle dot] dl-1, P < 0.05), a 5% reduction in low-density lipoprotein cholesterol (129 +/- 5 vs 122 +/- 5 mg [middle dot] dl-1, P < 0.05), and an 8% decrease in the total cholesterol/highdensity lipoprotein-cholesterol ratio (5.1 +/- 0.3 vs 4.7 +/- 0.3, P < 0.01), despite no changes in [latin capital V with dot above]O2max, body weight, or percent body fat. Glucose-stimulated plasma insulin concentrations during oral glucose tolerance testing were significantly lower, and supine diastolic blood pressure was reduced (P < 0.05) as a result of the training program. No changes in any of these variables occurred in a sedentary control group. These findings indicate that resistive training can lower risk factors for coronary artery disease independent of changes in [latin capital V with dot above]O2max, body weight, or body composition. (C)1988The American College of Sports Medicine
Leucine has been shown to stimulate adipose tissue protein synthesis in vivo as well as leptin secretion, protein synthesis, hyper-plastic growth, and tissue morphogenesis in in vitro experiments using freshly isolated adipocytes. Recently, others have proposed that leucine oxidation in the mitochondria may be required to activate the mammalian target of rapamycin (mTOR), the cytosolic Ser/Thr protein kinase that appears to mediate some of these effects. The first irreversible and rate-limiting step in leucine oxidation is catalyzed by the branched-chain alpha-keto acid dehydrogenase (BCKD) complex. The activity of this complex is regulated acutely by phosphorylation of the E1alpha-subunit at Ser293 (S293), which inactivates the complex. Because the alpha-keto acid of leucine regulates the activity of BCKD kinase, it has been suggested as a potential target for leucine regulation of mTOR. To study the regulation of BCKD phosphorylation and its potential link to mTOR activation, a phosphopeptide-specific antibody recognizing this site was developed and characterized. Phospho-S293 (pS293) immunoreactivity in liver corresponded closely to diet-induced changes in BCKD activity state. Immunoreactivity was also increased in TREMK-4 cells after the induction of BCKD kinase by a drug-inducible promoter. BCKD S293 phosphorylations in adipose tissue and gastrocnemius (which is mostly inactive in vivo) were similar. This suggests that BCKD complex in epididymal adipose tissue from food-deprived rats is mostly inactive (unable to oxidize leucine), as is the case in muscle. To begin to test the leucine oxidation hypothesis of mTOR activation, the dose-dependent effects of orally administered leucine on acute activation of S6K1 (an mTOR substrate) and BCKD were compared using the pS293 antibodies. Increasing doses of leucine directly correlated with increases in plasma leucine concentration. Phosphorylation of S6K1 (Thr389, the phosphorylation site leading to activation) in adipose tissue was maximal at a dose of leucine that increased plasma leucine approximately threefold. Changes in BCKD phosphorylation state required higher plasma leucine concentrations. The results seem more consistent with a role for BCKD and BCKD kinase in the activation of leucine metabolism/oxidation than in the activation of the leucine signal to mTOR.
The objective of this study was to assess the effects of weight history status and ethnicity on the ability of the Harris Benedict (HB) formula to: 1) predict measured resting energy expenditure (REE), and, 2) accurately estimate energy needs over a 2-week test period. Subjects were never-overweight (BMI </= 25 kg/m(2), n=47), overweight (BMI 27-30 kg/m(2), n=170), and weight-reduced (BMI </= 25 kg/m(2), n=51) healthy, adult African-American (AA) and Caucasian (C) women. Food was provided for 2 weeks at an energy level calculated using the HB formula multiplied by a 1.35 activity factor. After 2 weeks, weight, REE (by indirect calorimetry), and body composition (by dual-energy X-ray absorptiometry) were assessed. Data were analyzed using 2-way ANOVA at p<0.05 significance. The HB formula overestimated REE 1) in each weight history group (by 160 +/-125 kcals among never-overweight, 295 +/-189 kcal among overweight, and 105 +/-135 among weight-reduced) such that there was a group effect on overestimation (P<0.001) and 2) between ethnicities, with a greater overestimation in AA vs. C (P<0.001). There was a significant effect of weight history group on weight change (P<0.001) over 2-weeks, such that weight-reduced women gained more weight than the other two groups (P<0.05). In conclusion, the ability of the HB formula to estimate REE differed with weight history status and ethnicity. The accuracy of the HB formula to predict dietary energy needs was affected by weight history status. These results suggest that formulas used to calculate energy needs should take into account weight history and ethnicity.
The internal validity of a 24-hr. dietary recall and a seven-day dietary record was investigated among a group of non-institutionalized elderly subjects who were participating in a congregate meals program. Internal validity was assessed by comparing reported intake with unobtrusively obtained data on actual intake. Validity results suggest that the recall is prone to over-reporting low intakes and under-reporting high intakes. This pattern has been referred to as the "flat-slope syndrome." Records collected during the first few dyas were less prone to this syndrome; however, validity declined by the fifth, sixth, and seventh record days. Also, as the record progressed to the seventh day, the demographic nature of the sample became biased due to drop-outs and decreased usability of the records.
Leucine has been proposed as an in vivo regulator of protein metabolism, although the evidence for this in humans remains inconclusive. To test this hypothesis, we infused either L-leucine (154 +/- 1 mumol.kg-1 x h-1) or saline intravenously in six healthy men in two separate studies. L-Leucine infusion increased plasma concentrations of leucine and alpha-ketoisocaproate from 112 +/- 6 and 38 +/- 3 mumol/l to 480 +/- 27 (P < 0.001) and 94 +/- 13 mumol/l (P < 0.001), respectively, without any significant change in circulating insulin or C peptide levels. Leucine infusion decreased plasma concentrations of several amino acids and decreased whole body valine flux and valine oxidation (using L-[1-13C]valine as a tracer) and phenylalanine flux (using [2H5]-phenylalanine as a tracer). According to arteriovenous differences across the leg, the net balance of phenylalanine, valine, and lysine shifted toward greater retention during leucine infusion, whereas alanine balance did not change. Valine release and phenylalanine release from the leg (estimated from the dilution of respective tracers) decreased, indicating inhibition of protein degradation by leucine infusion. We conclude that leucine decreases protein degradation in humans and that this decreased protein degradation during leucine infusion contributes to the decrease in plasma essential amino acids. This study suggests a potential role for leucine as a regulator of protein metabolism in humans.