***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: This study was design ed to evaluate the effects of enriching an essential amino acid ( EAA ) mixture with leucine on muscle protein metabolism in elderly and young individuals . Four ( 2 elderly and 2 young ) groups were studied before and after ingestion of 6.7 g of EAAs . EAAs were based on the composition of whey protein [ 26 % leucine ( 26 % Leu ) ] or were enriched in leucine [ 41 % leucine ( 41 % Leu ) ] . A primed , continuous infusion of L-[ring-2H5]phenylalanine was used together with vastus lateralis muscle biopsies and leg arteriovenous blood sample s for the determinations of fractional synthetic rate ( FSR ) and balance of muscle protein . FSR increased following amino acid ingestion in both the 26 % ( basal : 0.048 + /- 0.005%/h ; post-EAA : 0.063 + /- 0.007%/h ) and the 41 % ( basal : 0.036 + /- 0.004%/h ; post-EAA : 0.051 + /- 0.007%/h ) Leu young groups ( P < 0.05 ) . In contrast , in the elderly , FSR did not increase following ingestion of 26 % Leu EAA ( basal : 0.044 + /- 0.003%/h ; post-EAA : 0.049 + /- 0.006%/h ; P > 0.05 ) but did increase following ingestion of 41 % Leu EAA ( basal : 0.038 + /- 0.007%/h ; post-EAA : 0.056 + /- 0.008%/h ; P < 0.05 ) . Similar to the FSR responses , the mean response of muscle phenylalanine net balance , a reflection of muscle protein balance , was improved ( P < 0.05 ) in all groups , with the exception of the 26 % Leu elderly group . We conclude that increasing the proportion of leucine in a mixture of EAA can reverse an attenuated response of muscle protein synthesis in elderly but does not result in further stimulation of muscle protein synthesis in young subjects We recently demonstrated that muscle protein synthesis was stimulated to a similar extent in young and elderly subjects during a 3-h amino acid infusion . We sought to determine if a more practical bolus oral ingestion would also produce a similar response in young ( 34 + /- 4 yr ) and elderly ( 67 + /- 2 yr ) individuals . Arteriovenous blood sample s and muscle biopsies were obtained during a primed ( 2.0 micromol/kg ) constant infusion ( 0.05 micromol.kg(-1).min(-1 ) ) of L-[ring-2H5]phenylalanine .  Muscle protein kinetics and mixed muscle fractional synthetic rate ( FSR ) were calculated before and after the bolus ingestion of 15 g of essential amino acids ( EAA ) in young ( n = 6 ) and elderly ( n = 7 ) subjects . After EAA ingestion , the rate of increase in femoral artery phenylalanine concentration was slower in elderly subjects but remained elevated for a longer period . EAA ingestion increased FSR in both age groups by approximately 0.04%/h ( P < 0.05 ) . However , muscle intracellular ( IC ) phenylalanine concentration remained significantly higher in elderly subjects at the completion of the study ( young : 115.6 + /- 5.4 nmol/ml ; elderly : 150.2 + /- 19.4 nmol/ml ) . Correction for the free phenylalanine retained in the muscle IC pool result ed in similar net phenylalanine uptake values in the young and elderly . EAA ingestion increased plasma insulin levels in young ( 6.1 + /- 1.2 to 21.3 + /- 3.1 microIU/ml ) but not in elderly subjects ( 3.0 + /- 0.6 to 4.3 + /- 0.4 microIU/ml ) . Despite differences in the time course of plasma phenylalanine kinetics and a greater residual IC phenylalanine concentration , amino acid supplementation acutely stimulated muscle protein synthesis in both young and elderly individuals CONTEXT Inadequate dietary protein intake has been implicated in sarcopenia . OBJECTIVE AND DESIGN The objectives of this study were to determine whether : 1 ) chronic essential amino acid ( EAA ) supplementation improves postabsorptive muscle protein fractional synthesis rate ( FSR ) , lean body mass ( LBM ) , and one-repetition maximum muscle strength , and and rogen receptor and IGF-I muscle protein expression ; and 2 ) the acute anabolic response to EAA ingestion is preserved after a 3-month supplementation period . Using a r and omized , double-blinded , placebo-controlled design , older women ( 68 + /- 2 yr ) were assigned to receive either placebo ( n = 7 ) , or 15 g EAA/d [ supplemented treatment group ( SUP ) ] ( n = 7 ) for 3 months . Metabolic outcomes were assessed in association with stable isotope studies conducted at 0 and 3 months . SETTING The study was performed at The University of Texas Medical Branch General Clinical Research Center . RESULTS Ingestion of 7.5 g EAA acutely stimulated FSR in both groups at 0 months ( P < 0.05 ) . Basal FSR at 3 months was increased in SUP only . The magnitude of the acute response to EAA was unaltered after 3 months in SUP . LBM increased in SUP only ( P < 0.05 ) . One-repetition maximum strength remained unchanged in both groups . Basal IGF-I protein expression increased in SUP after 3 months ( P = 0.05 ) , with no changes in and rogen receptor or total and phosphorylated Akt , mammalian target of rapamycin , S6 kinase , and 4E-binding protein . CONCLUSIONS EAA improved LBM and basal muscle protein synthesis in older individuals . The acute anabolic response to EAA supplementation is maintained over time and can improve LBM , possibly off setting the debilitating effects of sarcopenia BACKGROUND It has been reported that the blunted muscle protein synthetic response to food intake in the elderly can be normalized by increasing the leucine content of a meal . OBJECTIVE The objective was to assess the effect of 3 mo of leucine supplementation on muscle mass and strength in healthy elderly men . DESIGN Thirty healthy elderly men with a mean ( + /-SEM ) age of 71 + /- 4 y and body mass index ( BMI ; in kg/m(2 ) ) of 26.1 + /- 0.5 were r and omly assigned to either a placebo-supplemented ( n = 15 ) or leucine-supplemented ( n = 15 ) group . Leucine or placebo ( 2.5 g ) was administered with each main meal during a 3-mo intervention period . Whole-body insulin sensitivity , muscle strength ( one-repetition maximum ) , muscle mass ( measured by computed tomography and dual-energy X-ray absorptiometry ) , myosin heavy chain isoform distribution , and plasma amino acid and lipid profiles were assessed before , during , and /or after the intervention period . RESULTS No changes in skeletal muscle mass or strength were observed over time in either the leucine- or placebo-supplemented group . No improvements in indexes of whole-body insulin sensitivity ( oral glucose insulin sensitivity index and the homeostasis model assessment of insulin resistance ) , blood glycated hemoglobin content , or the plasma lipid profile were observed . CONCLUSION Long-term leucine supplementation ( 7.5 g/d ) does not augment skeletal muscle mass or strength and does not improve glycemic control or the blood lipid profile in healthy elderly men . This trial was registered at clinical trials.gov as NCT00807508 BACKGROUND The progressive loss of skeletal muscle mass with aging is attributed to a disruption in the regulation of skeletal muscle protein turnover . OBJECTIVE We investigated the effects on whole-body protein balance and mixed-muscle protein synthesis rates of the ingestion of carbohydrate with or without protein and free leucine after simulated activities of daily living . DESIGN Eight elderly ( 75 + /- 1 y ) and 8 young ( 20 + /- 1 y ) lean men were r and omly assigned to 2 crossover experiments in which they consumed either carbohydrate ( CHO ) or carbohydrate plus protein and free leucine ( CHO+Pro+Leu ) after performing 30 min of st and ardized activities of daily living . Primed , continuous infusions with L-[ring-13C6]phenylalanine and L-[ring-2H2]tyrosine were applied , and blood and muscle sample s were collected to assess whole-body protein turnover and the protein fractional synthetic rate in the vastus lateralis muscle over a 6-h period . RESULTS Whole-body phenylalanine and tyrosine flux were significantly higher in the young than in the elderly men ( P < 0.01 ) . Protein balance was negative in the CHO experiment but positive in the CHO+Pro+Leu experiment in both groups . Mixed-muscle protein synthesis rates were significantly greater in the CHO+Pro+Leu than in the CHO experiment in both the young ( 0.082 + /- 0.005%/h and 0.060 + /- 0.005%/h , respectively ; P < 0.01 ) and the elderly ( 0.072 + /- 0.006%/h and 0.043 + /- 0.003%/h , respectively ; P < 0.01 ) subjects , with no significant differences between groups . CONCLUSIONS Co-ingestion of protein and leucine with carbohydrate after activities of daily living improves whole-body protein balance , and the increase in muscle protein synthesis rates is not significantly different between lean young and elderly men BACKGROUND Nutritional supplementation may be used to treat muscle loss with aging ( sarcopenia ) . However , if physical activity does not increase , the elderly tend to compensate for the increased energy delivered by the supplements with reduced food intake , which results in a calorie substitution rather than supplementation . Thus , an effective supplement should stimulate muscle anabolism more efficiently than food or common protein supplements . We have shown that balanced amino acids stimulate muscle protein anabolism in the elderly , but it is unknown whether all amino acids are necessary to achieve this effect . OBJECTIVE We assessed whether nonessential amino acids are required in a nutritional supplement to stimulate muscle protein anabolism in the elderly . DESIGN We compared the response of muscle protein metabolism to either  18 g essential amino acids ( EAA group : n = 6 , age 69 + /- 2 y ; + /- SD ) or 40 g balanced amino acids  ( 18 g essential amino acids  + 22 g  nonessential amino acids , BAA group ; n = 8 , age 71 + /- 2 y ) given orally in small boluses every 10 min for 3 h to healthy elderly volunteers .  Muscle protein metabolism was measured in the basal state and during amino acid administration via L-[ring-(2)H(5)]phenylalanine infusion , femoral arterial and venous catheterization , and muscle biopsies . RESULTS Phenylalanine net balance ( in nmol x min(-1 ) . 100 mL leg volume(-1 ) ) increased from the basal state ( P < 0.01 ) , with no differences between groups ( BAA : from -16 + /- 5 to 16 + /- 4 ; EAA : from -18 + /- 5 to 14 + /- 13 ) because of an increase ( P < 0.01 ) in muscle protein synthesis and no change in breakdown . CONCLUSION Essential amino acids are primarily responsible for the amino acid-induced stimulation of muscle protein anabolism in the elderly BACKGROUND & AIMS This study assessed the efficacy of supplemented essential amino acids on depressive symptoms , nutrition , muscle function , daily physical activity , and health-related quality of life ( HRQoL ) of institutionalized elderly patients . METHODS Forty-one patients ( 58.5 % women ; mean age 79.8 yrs ) with sequelae of coronary artery disease ( 73 % ) , femoral fracture ( 34 % ) , were r and omly assigned to receive oral essential amino acids 4 gr 2 times a day for 8 weeks or isocaloric placebo . Before r and omization and 8 weeks after the protocol started , the following variables were measured : depressive symptoms ( Geriatric Depression Scale , GDS ) , nutritional panel ( Mini Nutritional Assessment , MNA ; serum albumin and prealbumin levels ) , muscle strength ( H and Grip , HG ) , Activity Daily Life ( ADL ) , Quality of Life ( SF-36 , HRQoL ) and amino acid profile . RESULTS Compared with the placebo group , EAA patients improved nutrition ( MNA score 22.6 ± 1.5 post vs 21.8 ± 1.6 pre ; p < 0 . 04 , albumin g/dl 4.04 ± 0.35 post vs 3.88 ± 0 
    Output:
    
With respect to body weight and lean body mass ,  leucine supplementation turned out to be more effective in the subgroup of study participants with manifested sarcopenia .
All other parameters under investigation were not affected by leucine supplementation in a fashion significantly different from controls .
Conclusions It is concluded that leucine supplementation was found to exert beneficial effects on body weight , body mass index , and lean body mass  in older persons in those subjects already prone to sarcopenia , but not muscle strength .