The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis

Abstract

In the present study, we performed a meta-analysis to assess the ability of leucine supplementation to increase the muscle protein fraction synthetic rate and to augment lean body mass or leg lean mass in elderly patients. A literature search was conducted on Medline, Cochrane, EMBASE and Google Scholar databases up to 31 December 2013 for clinical trials that investigated the administration of leucine as a nutrient that affects muscle protein metabolism and muscle mass in elderly subjects. The included studies were randomised controlled trials. The primary outcome for the meta-analysis was the protein fractional synthetic rate. Secondary outcomes included lean body mass and leg lean mass. A total of nine studies were included in the meta-analysis. The results showed that the muscle protein fractional synthetic rate after intervention significantly increased in the leucine group compared with the control group (pooled standardised difference in mean changes 1·08, 95 % CI 0·50, 1·67; P, 0·001). No difference was found between the groups in relation to lean body mass (pooled standardised difference in mean changes 0·18, 95 % CI 20·18, 0·54; P¼ 0·318) or leg lean mass (pooled standardised difference in mean changes 0·006, 95 % CI 2 0·32, 0·44; P¼ 0·756). These findings suggest that leucine supplementation is useful to address the age-related decline in muscle mass in elderly individuals, as it increases the muscle protein fractional synthetic rate. Key words: Essential amino acids: Elderly: Dietary supplements: SarcopeniaAgeing is accompanied by a progressive decline in muscle mass and strength (sarcopenia) and is associated with a lower quality of life due to the reduced ability of an individual to perform daily living activities (1) . It also predisposes people to the development of chronic metabolic disorders such as diabetes and obesity (2) . The prevalence of sarcopenia differs by sex and living settings (3) . For example, age-related muscle loss has been reported to be prevalent in about 68 % of elderly men and 21 % of elderly women living in nursing homes (4,5) , but in about 10 % of men and 33 % of women living in the community (4,6)

Fall and Fracture Risk in Sarcopenia and Dynapenia With and Without Obesity: the Role of Lifestyle Interventions

“…There is also considerable evidence that different protein sources vary in their capacity to stimulate MPS, with whey protein being more effective than either casein or soy [87]. Supplementation with 20-40 g of high-quality, rapidly digested, leucine-rich protein can improve physical performance in older adults [88], but a number of studies have failed to observe any beneficial effects of protein supplementation alone on muscle probably due to differences in the type, timing, dose and/or distribution of protein intake [89]. While further studies are needed to determine optimal protein supplementation strategies for older adults, a recent consensus statement recommends a daily protein intake of 1.0-1.2 g/kg with at least 20-25 g of high-quality protein at each meal [90].…”

Utilization of Hydroxyl-Methyl Butyrate, Leucine, Glutamine and Arginine Supplementation in Nutritional Management of Sarcopenia—Implications and Clinical Considerations for Type 2 Diabetes Mellitus Risk Modulation

“…Furthermore, in a systematic review and meta-analysis, Leu supplementation was determined to be effective on muscle protein synthesis assessed by FSR, without affecting lean body mass or leg lean mass accretion in elderly patients participating in nine randomized controlled trials. Hence, such therapeutic schemes may be beneficial for elderly with sarcopenia [43]. Recently, Murphy et al documented that, in healthy old subjects, Leu supplementation increased the integrated muscle protein synthesis response [44].…”

“…In humans, the use of Leu alone resulted in increased levels of plasma Leu, ultimately leading to a disproportionate balance for other amino acids. There is no evidence from long-term exposures to high doses of Leu as to how it may affect lean leg mass [43]. Currently, it is not recommended to use Leu alone, especially in long-term elderly supplementation.…”

“…The utilization of nutritional support mixtures leading to clinical picture improvements in nutritional parameters, especially for increasing albumin-prealbumin concentrations, are effective in malnutrition management and attract interest from clinicians. When mixtures containing essential, semi-essential and branched chain amino acids are used, blood plasma amino acid levels increase (especially Leu), while 3-methylhistidine and cortisol are decreased [43]. Decreases in cortisol and 3-methylhistidine indicate decreased protein degradation signaling in muscle.…”

Amino acids in healthy aging skeletal muscle

“…Even when isolated from other essential amino acids, leucine can independently activate mTORC1 (51) and enhance muscle protein synthesis (52). Multiple studies have shown that essential amino acid bolus feedings that include 3 grams of leucine significantly increase muscle protein fractional synthetic rate in older adults (53)(54)(55). In young adults, 10 grams of essential amino acids (~2 grams of leucine) mixed in a noncaloric, noncaffeinated carbonated beverage was sufficient to induce maximal postprandial muscle protein synthesis (56).…”