Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial.
What this study found
Overall, enriching a low-protein beverage with a high leucine dose improved myofibrillar protein synthesis, whereas adding BCAAs was less effective. Myofibrillar fractional synthetic rate showed a treatment by time interaction over 0 to 1.5 and 1.5 to 4.5 h after feeding and exercise (P = 0.002) and over 0 to 4.5 h (P = 0.005). In the late postprandial period and over the full 0 to 4.5 h window, W25 and W6+High-Leu produced higher FSR than W6+Low-Leu, W6+BCAAs, and W6. No significant differences were observed between fed and postexercise conditions (P = 0.483 and P = 0.419).
- Study & population
- Double-blind, randomized parallel-group trial in 40 healthy young men aged 18 to 35 years.
- Intervention
- Five oral beverage conditions were tested immediately after resistance exercise: 6.25 g whey protein with 0.75 g leucine; 6.25 g whey protein with total leucine 3.0 g; 25 g whey protein with total leucine 3.0 g; 6.25 g whey protein with added branched-chain amino acids to 5.0 g total leucine; and 6.25 g whey protein…
- Key limitation
- Small acute study with only 8 participants per arm, so precision is limited.
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Open PDFOriginal abstract
BACKGROUND Leucine is a key amino acid involved in the regulation of skeletal muscle protein synthesis. OBJECTIVE We assessed the effect of the supplementation of a lower-protein mixed macronutrient beverage with varying doses of leucine or a mixture of branched chain amino acids (BCAAs) on myofibrillar protein synthesis (MPS) at rest and after exercise. DESIGN In a parallel group design, 40 men (21 ± 1 y) completed unilateral knee-extensor resistance exercise before the ingestion of 25 g whey protein (W25) (3.0 g leucine), 6.25 g whey protein (W6) (0.75g leucine), 6.25 g whey protein supplemented with leucine to 3.0 g total leucine (W6+Low-Leu), 6.25 g whey protein supplemented with leucine to 5.0 g total leucine (W6+High-Leu), or 6.25 g whey protein supplemented with leucine, isoleucine, and valine to 5.0 g total leucine. A primed continuous infusion of l-[ring-(13)C6] phenylalanine with serial muscle biopsies was used to measure MPS under baseline fasted and postprandial conditions in both a rested (response to feeding) and exercised (response to combined feeding and resistance exercise) leg. RESULTS The area under the blood leucine curve was greatest for the W6+High-Leu group compared with the W6 and W6+Low-Leu groups (P < 0.001). In the postprandial period, rates of MPS were increased above baseline over 0-1.5 h in all treatments. Over 1.5-4.5 h, MPS remained increased above baseline after all treatments but was greatest after W25 (∼267%) and W6+High-Leu (∼220%) treatments (P = 0.002). CONCLUSIONS A low-protein (6.25 g) mixed macronutrient beverage can be as effective as a high-protein dose (25 g) at stimulating increased MPS rates when supplemented with a high (5.0 g total leucine) amount of leucine. These results have important implications for formulations of protein beverages designed to enhance muscle anabolism. This trial was registered at clinicaltrials.gov as NCT 1530646.