Overview
L-Leucine is a branched-chain essential amino acid that plays a central role in regulating muscle protein synthesis (MPS) by activating the mTOR signaling pathway. It functions both as a substrate for protein synthesis and as a signaling molecule that stimulates anabolic pathways, making it a key target for interventions aimed at sarcopenia, malnutrition, and muscle wasting conditions. Evidence suggests that leucine supplementation may improve muscle mass, strength, and physical performance in older adults with sarcopenia, particularly when combined with resistance training [1][7]. In older populations, leucine enhances the anabolic response to protein intake, especially in low-protein meals, and may help counteract anabolic resistance associated with aging [10][8]. While some studies show benefits in lean mass and strength, results on functional outcomes like insulin sensitivity are mixed, with no additional improvement beyond resistance training alone in prefrail and frail older women [5]. In chronic liver disease, leucine and other branched-chain amino acids may help mitigate sarcopenia and malnutrition due to impaired protein metabolism [2]. Preliminary evidence also indicates potential for leucine to support protein anabolism in patients with advanced cancer before refractory cachexia develops [4]. However, effects are most pronounced when baseline nutrition or muscle mass is suboptimal.
Dosage Guide
Therapeutic Doses
For treatment of specific conditions
Special Forms
Alternative forms for specific needs
Precise dosing for research or clinical use
Includes leucine with isoleucine and valine; common in sports nutrition
Clinical Notes
- High doses may cause gastrointestinal discomfort in some individuals
- Long-term safety of high-dose leucine supplementation is not fully established
- Leucine should be part of a balanced protein intake; isolated use without adequate total protein may limit benefits
- Monitor in patients with maple syrup urine disease (contraindicated)
- Potential interaction with Parkinson’s medications (e.g., levodopa); separate dosing by several hours
Research
Leucine supplementation improves sarcopenia-related parameters in older adults, including muscle mass and strength.
L-leucine and BCAA supplementation may improve malnutrition and sarcopenia in chronic liver disease.
5 g/day leucine with resistance training increased fat-free mass and strength in untrained midlife women.
Leucine acts as a signaling molecule to promote protein synthesis in cancer patients before refractory cachexia.
Leucine supplementation did not improve insulin sensitivity beyond resistance training in prefrail/frail older women.
Adding leucine to a low-protein beverage enhanced myofibrillar protein synthesis in young men post-exercise.
Leucine supplementation showed beneficial effects on sarcopenia criteria, including lean mass and physical performance.
Meta-analysis found leucine increases muscle protein synthesis and lean body mass in older adults.
Leucine supplementation (5 g/day) combined with resistance training improved body composition and strength in peri- and postmenopausal women.
5 g of leucine in a low-protein drink maximized myofibrillar protein synthesis after resistance exercise.
Products Containing L-Leucine(10 reports)
This supplement combines two amino acids—L-Glutamine and L-Leucine—each dosed at 2.5 g per serving. L-Glutamine supports gut barrier integrity and immune function, particularly under catabolic stress, while L-Leucine acts as a key regulator of muscle protein synthesis, making it relevant for muscle maintenance and sarcopenia prevention. Both ingredients are in free-form powder, supporting rapid absorption.
L-Leucine by Nutricost is a standalone amino acid supplement providing 2,000 mg per serving, designed to support muscle protein synthesis and combat age-related muscle loss. As a primary branched-chain amino acid (BCAA), leucine acts both as a substrate and signaling molecule to stimulate anabolic pathways via mTOR activation. While the dose is sub-therapeutic compared to most clinical trials, it may still offer benefits when combined with resistance training and adequate dietary protein.
L-Leucine, Unflavored by Nutricost is a standalone amino acid supplement delivering 5 g of L-leucine per serving, a clinically studied dose shown to stimulate muscle protein synthesis and support muscle mass, particularly in older adults and those engaging in resistance training. As a supplement, it is designed to enhance the anabolic response to protein intake or exercise, especially in populations with increased protein needs or anabolic resistance.
Free-Form L-Leucine by Source Naturals is a standalone supplement delivering 1.5 g of L-leucine per serving, an essential branched-chain amino acid critical for initiating muscle protein synthesis via mTOR activation. While leucine is a key driver of anabolic signaling—especially in aging or catabolic populations—the dose provided is below the clinically studied range required for optimal efficacy in sarcopenia or resistance training support.
L-Leucine, Unflavored by Primaforce is a standalone amino acid supplement delivering 5 g of L-leucine per serving, a clinically effective dose shown to stimulate muscle protein synthesis and support muscle mass, particularly in older adults and those engaging in resistance training. As a supplement, it is designed to enhance the anabolic response to protein intake or exercise, especially in populations with suboptimal protein intake or age-related anabolic resistance.
This supplement combines L-Glutamine and L-Leucine, two amino acids with distinct roles in gut health and muscle protein synthesis. L-Glutamine is the primary ingredient based on naming and functional focus, supporting intestinal barrier integrity and immune function. While both ingredients are included at moderate doses, neither reaches the typical clinical range for their most evidence-backed indications when taken at one serving per day.
NOW Foods Sports L-Leucine Powder provides 5 grams of pure L-leucine per serving, a clinically effective dose shown to stimulate muscle protein synthesis and support muscle mass, particularly in older adults and those engaged in resistance training. As a supplement, it is designed to enhance the anabolic response to exercise and low-protein meals by activating the mTOR pathway.
Essentials, Leucine+ is a targeted amino acid supplement delivering 5 g of L-leucine per serving, a clinically effective dose shown to stimulate muscle protein synthesis and support muscle mass, particularly in older adults and those engaging in resistance training. The formulation focuses on leucine as the primary active ingredient, aligning with evidence for combating age-related muscle loss and enhancing anabolic response to protein intake.
This BCAA powder delivers a 2:1:1 ratio of L-Leucine (2.5 g), L-Isoleucine (1.25 g), and L-Valine (1.25 g) per serving, with L-Leucine as the primary active ingredient driving muscle protein synthesis. The formulation is designed to support exercise recovery, muscle maintenance, and performance, aligning with evidence-based dosing for active individuals and older adults at risk of sarcopenia.
This supplement features a proprietary blend of Angelica gigas, Cynanchum wilfordii, and Phlomis umbrosa (EstroG-100), a clinically studied herbal complex shown to reduce menopausal symptoms such as hot flashes, vaginal dryness, and mood disturbances. The formulation is designed to provide non-hormonal support, making it a potential alternative for women seeking relief without estrogenic effects on reproductive tissues.