Thread: Leucine – enough's enough

Leucine – enough's enough
by Anthony Roberts ~ source

First of all, let me preface this by saying that I don’t care if leucine is anabolic or not. I have never formulated nor sold a protein powder with or without leucine, and have no plans to. Leucine has been the darling of the amino acid world for the past few years, thanks in part to its ability to activate mTOR (mamalian Target of Rapamysin), which signals the anabolic process. Leucine acts as a system of checks and balances in the body – if your body senses lower levels of this amino, it puts a stop to the anabolic process. This makes it important for muscle growth, because if you don’t have enough leucine, your body isn’t going to receive the (mTOR) signal to build new muscle tissue.

But that minimal level of leucine is likely to be achieved without supplemental leucine (i.e. adding leucine to your protein shake), and may be met with the amount of leucine found in a typical whey protein shake or serving of Essential Amino Acids. None of this means that it’s “bad” or “useless” of course, it simply means that adding a buttload of leucine to a diet that already contains high-quality proteins (whey, red meat, and surprisingly, even pink lentils contain quite a bit of leucine). So while it’s something that you want to consume, there’s a lot of research indicating that consuming it in amounts over and above what’s found in quality protein sources, is unlikely to impart additional benefits in terms of muscle growth. Here are two studies to this effect:

Nutr Rev. 2011 Sep;69(9):550-7. doi: 10.1111/j.1753-4887.2011.00420.x.
Supplemental dietary leucine and the skeletal muscle anabolic response to essential amino acids.
Pasiakos SM, McClung JP.
Source

SM Pasiakos and JP McClung are with the Military Nutrition Division, US Army Research Institute of Environmental Medicine (USARIEM), Natick, Massachusetts, USA.

Abstract

Skeletal muscle protein synthesis (MPS) is regulated by a number of dietary factors, to include essential amino acids (EAAs). Leucine, a branched-chain amino acid, has been identified as a stimulator of MPS in many cell culture and animal studies. However, whether supplemental leucine exerts a unique stimulatory effect, as compared to other EAAs, on muscle anabolism in humans has not been clearly demonstrated. A recent study found no improvement in resting MPS in adults who consumed a 10 g EAA supplement providing added leucine (3.5 g leucine) when compared to a control 10 g EAA supplement (1.8 g leucine). These findings suggest that added leucine is unnecessary for the stimulation of MPS when sufficient EAAs are provided; however, the study of supplemental leucine during conditions such as endurance exercise, caloric deprivation, and ageing may be warranted.

J Nutr. 2010 Nov;140(11):1970-6. Epub 2010 Sep 15.
Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women.
Glynn EL, Fry CS, Drummond MJ, Timmerman KL, Dhanani S, Volpi E, Rasmussen BB.
Source

Departments of Physical Therapy, University of Texas Medical Branch, Galveston, TX 77555, USA.

Abstract

Essential amino acids (EAA) stimulate skeletal muscle protein synthesis (MPS) in humans. Leucine may have a greater stimulatory effect on MPS than other EAA and/or decrease muscle protein breakdown (MPB). To determine the effect of 2 different leucine concentrations on muscle protein turnover and associated signaling, young men (n = 6) and women (n = 8) ingested 10 g EAA in 1 of 2 groups: composition typical of high quality proteins (CTRL; 1.8 g leucine) or increased leucine concentration (LEU; 3.5 g leucine). Participants were studied for 180 min postingestion. Fractional synthetic rate and leg phenylalanine and leucine kinetics were assessed on muscle biopsies using stable isotopic techniques. Signaling was determined by immunoblotting. Arterial leucine concentration and delivery to the leg increased in both groups and was significantly higher in LEU than in CTRL; however, transport into the muscle and intracellular availability did not differ between groups. MPS increased similarly in both groups 60 min postingestion. MPB decreased at 60 min only in LEU, but net muscle protein balance improved similarly. Components of mammalian target of rapamycin (mTOR) signaling were improved in LEU, but no changes were observed in ubiquitin-proteasome system signaling. Changes in light chain 3 and mTOR association with Unc-51-like kinase 1 indicate autophagy decreased more in LEU. We conclude that in 10 g of EAA, the leucine content typical of high quality proteins (~1.8 g) is sufficient to induce a maximal skeletal muscle protein anabolic response in young adults, but leucine may play a role in autophagy regulation.

Good read.