Beneficial Effects of Leucine Supplementation on Criteria for Sarcopenia: A Systematic Review

Abstract

Objective: Treating sarcopenia remains a challenge, and nutritional interventions present promising approaches. We summarize the effects of leucine supplementation in treating older individuals with sarcopenia associated with aging or to specific disorders, and we focus on the effect of leucine supplementation on various sarcopenia criteria, e.g., muscular strength, lean mass, and physical performance. Methods: A literature search for articles related to this topic was performed on the relevant databases, e.g., the PubMed/Medline, Embase, EBSCO, Cochrane, Lilacs, and Dialnet. The identified articles were reviewed according to Preferred Reporting Items for Systematic reviews and meta-analyses (PRISMA) guidelines. Results: Of the 163 articles we consulted, 23 met our inclusion criteria, analysing the effect of leucine or leucine-enriched protein in the treatment of sarcopenia, and 13 of these studies were based on randomized and placebo-controlled trials (RCTs). In overall terms, the published results show that administration of leucine or leucine-enriched proteins (range 1.2–6 g leucine/day) is well-tolerated and significantly improves sarcopenia in elderly individuals, mainly by improving lean muscle-mass content and in this case most protocols also include vitamin D co-administration. The effect of muscular strength showed mix results, and the effect on physical performance has seldom been studied. For sarcopenia-associated with specific disorders, the most promising effects of leucine supplementation are reported for the rehabilitation of post-stroke patients and in those with liver cirrhosis. Further placebo-controlled trials will be necessary to determine the effects of leucine and to evaluate sarcopenia with the criteria recommended by official Working Groups, thereby limiting the variability of methodological issues for sarcopenia measurement across studies.

Effects of Leucine Administration in Sarcopenia: A Randomized and Placebo-controlled Clinical Trial

“…In these cases, nutritional interventions remain the most promising measure for delaying the progression of sarcopenia and preventing its adverse consequences, such as falls, mobility loss, and a bed-to-sofa lifestyle. The supplementation of whey protein which contains high amounts of the amino acid leucine or a mixtures of branched-chained amino acids with or without other nutritional supplements have been the most common interventions tested for treating sarcopenia in community-dwelling older individuals [13][14][15]29]. However, the effect of leucine alone, the amino acid shown to stimulate muscle synthesis and reduce its turnover in the most powerful way [30][31][32][33][34][35][36], has seldom been evaluated and no studies have been performed in institutionalized older individuals showing high rates of sarcopenia, functional impairment and of comorbidities all promoting muscle loss.…”

“…However, the effect of leucine alone, the amino acid shown to stimulate muscle synthesis and reduce its turnover in the most powerful way [30][31][32][33][34][35][36], has seldom been evaluated and no studies have been performed in institutionalized older individuals showing high rates of sarcopenia, functional impairment and of comorbidities all promoting muscle loss. In addition, most of the studies of leucine-enriched protein supplementation have been conducted in community-dwelling individuals [14] and the effects on institutionalized older individuals may present different results, as the rate of comorbidities and functional impairment is higher in institutionalized individuals. Supplementation with leucine has small but significant effects on muscle mass index, not because it improved these parameters in those individuals supplemented with leucine, but because in the placebo group there was a decline in this sarcopenia parameter.…”

“…Confirming this, metabolic studies showed that older individuals aged 65 years and over require approximately 2% more protein intake per meal to maximize muscle protein synthesis [13]. Furthermore, globally, only 40% of older adults meet the recommended daily protein intake and 10% of older women do not even meet the estimated minimal average requirement [14,15].…”

“…Most randomized placebo controlled trials (RCTs) have included interventions using whey protein as a supplement, because these contain large amounts of leucine (approximately 13 g leucine/100 g protein [13]). However, scientific evidence regarding the effect of leucine alone in sarcopenia is very scarce [11,[14][15][16]. We performed an RCT in order to ascertain whether the administration of leucine alone is effective in the treatment of sarcopenia and respiratory muscle function in older institutionalized individuals, a subgroup of older individuals with huge amount of comorbidity who are seldom evaluated in RCTs using leucine supplementation.…”

Sarcopenia: Again and Updated

“…Positive results have been reported on supplementation with leucine and its metabolite β-hydroxy β-methylbutyrate (HMB) due to their contribution to protein synthesis (13,31). HMB has been shown to improve muscle mass and to preserve muscle strength and function in older people with sarcopenia or frailty (17,18,32).…”