Leucine, the turbo for muscle building?
Leucine, the turbo for muscle building?
Leucine is an amino acid and belongs to the BCAAs. BCAAs are branched-chain amino acids (leucine, isoleucine and valine). These amino acids are therefore important for our muscles and are a component of many animal and plant foods.
Leucine for muscle building
It is assumed that leucine is the amino acid that contributes significantly to increasing the muscle protein synthesis rate. The plasma leucine concentration correlates with the muscle protein synthesis rate after protein intake (Pennings, 2011) . This supports the assumption that the leucine content of a protein portion is decisive for the anabolic effect of a protein source. Besides the amino acid leucine, however, other amino acids also play an important role.
The effect of leucine supplementation
The following study (Churchward-Venne, 2014) shows muscle protein synthesis rates with five different protein drinks:
6,25 g whey protein
6,25 g whey protein with 2,25 g leucine (3 g leucine in total)
6,25 g whey protein with 4,25 g leucine (5 g leucine in total)
6,25 g whey protein with 6 g BCAAs (4,25 g leucine, 1,38 g isoleucine and 1,35 g valine)
25 g whey protein (3 g leucine in total)
All five drinks increased the muscle protein synthesis rate. As expected, the 25 g dose of whey protein increased the muscle protein synthesis rate more than 6,25 g of whey protein. Adding 2,25 g of leucine did not increase the muscle protein synthesis rate any further. The 6,25 g of whey protein and the 2,25 g of leucine have the same total leucine content as 25 g of whey protein. The amount of leucine therefore does not determine the muscle protein synthesis rate on its own. Adding 4,25 g of leucine to the 6,25 g of whey protein increased muscle protein synthesis further. This produced a rate similar to that of 25 g of whey protein.
BCAAs reduce the effect on the muscle protein synthesis rate
Interestingly, adding 6 g of BCAAs (branched-chain amino acids) prevents the positive effect of leucine on muscle protein synthesis. Isoleucine, leucine and valine use the same transporter to be absorbed in the intestine. It is therefore speculated that leucine, isoleucine and valine compete for absorption. This in turn leads to a slower rise in leucine. However, the speed of the leucine rise appears to be an important criterion for a high muscle protein synthesis rate.
The leucine content is therefore an important criterion when dosing protein. Plant proteins generally contain smaller amounts, so higher amounts of these protein sources should be consumed or supplemented with leucine powder to achieve a better effect on the muscle protein synthesis rate.
Sources:
Pennings, Bart; Boirie, Yves; Senden, Joan M. G.; Gijsen, Annemie P.; Kuipers, Harm; van Loon, Luc J. C. (2011): Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. In: The American journal of clinical nutrition 93 (5), pp. 997–1005. DOI: 10.3945/ajcn.110.008102.
Churchward-Venne, Tyler A.; Breen, Leigh; Di Donato, Danielle M.; Hector, Amy J.; Mitchell, Cameron J.; Moore, Daniel R. et al. (2014): Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men. A double-blind, randomized trial. In: The American journal of clinical nutrition 99 (2), pp. 276–286. DOI: 10.3945/ajcn.113.068775.
