Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men
Previous studies show that supplementation with essential amino acids (EAAs) increases muscle protein synthesis and that this effect is boosted with resistance exercise. The EAA leucine has received special attention due to its potential to activate mTor (mammalian target of rapamycin), which is an initiation factor that jumpstarts muscle protein synthesis. There is, however, a dose-dependent relationship between leucine and muscle protein synthesis in that once the maximal point of saturation is reached, no further benefit is shown. Researchers set out to explore this dose-dependent effect to determine the amount of leucine that could stimulate muscle protein synthesis in young healthy males at rest and after resistance exercise.
Acute metabolic study
Number of Subjects
21 - 22
To test if leucine combined with a suboptimal dose of whey protein (6.25 grams of whey + 3 grams of leucine) could increase myofibrillar protein synthesis to the same extent as an optimal dose of whey protein (25 grams of whey). Researchers also tested the effects of a whey protein supplement combined with the other essential amino acids and no added leucine, and hypothesized that protein synthesis would increase, but to a lesser degree.
Participants were separated into 3 groups.
WHEY: Group 1 was given high-dose whey protein (25 grams)
LEU: Group 2 was given low-dose whey protein (6.25 grams) with added leucine (3 grams)
EAA-LEU: Group 3 was given low-dose whey protein (6.25 grams) with added essential amino acids except for leucine (0.75 grams leucine and 8.5 grams other EAAs)
There was no group given all the EAAs. Total and essential amino acid content of the nutritional treatments are shown in Table 1 below.
Both the LEU and EAA-LEU groups experienced increased myofibrillar protein synthesis in young healthy males at rest and 1-3 hours after exercise to the same degree as seen with 25 grams of whey.
Results indicate that both low-dose whey protein plus leucine and low-dose whey protein plus the essential amino acids without added leucine increased rates of muscle protein synthesis in healthy young men both at rest and 1-3 hours after a bout of resistance exercise. The effects matched the rates of muscle protein synthesis stimulated by a high-dose of whey protein, but only the high-dose whey protein maintained elevated rates of muscle protein synthesis 3-5 hours after exercise.
Results suggest that in young healthy men only 0.75 grams of leucine are needed to stimulate muscle protein synthesis when the other essential amino acids are given in larger amounts. The results further suggest that extra leucine is acting as a metabolic signal and is not the most limiting essential amino acid.
A lower dose of whey and higher dose of essential amino acids means a lower calorie and less satiating supplement, which can be of benefit to people who cannot eat a full protein meal due to illness, injury, physiological stressors, or dietary restrictions.
Churchward-Venne TA, Burd NA, Mitchell CJ, et al. Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men. J Physiol. 2012;590(11):2751-2765. doi:10.1113/jphysiol.2012.228833