Leucine (and It’s Colleagues): Driving Force of Muscle Protein Synthesis

Leucine (and It’s Colleagues): Driving Force of Muscle Protein Synthesis

Leucine (and It’s Colleagues): Driving Force of Muscle Protein Synthesis

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Written by Jonathan Kelly

You log onto your supplement supplier of choice and you are greeted with hundreds of brands supplying you with hundreds supplements. ALL claim to give you the greatest gains. Most won’t do much for you. Some will give you the impression they do (temporary pumps for example). However, a few will actually provide you with the opportunity to improve yourself more than if you didn’t use them. Leucine is one of the good guys.

P.S. If you’re looking for 10kg of lean muscle in 5 weeks or other such bro-science then you’re looking on the wrong supplement websites.

Leucine (and It’s Colleagues): Driving Force of Muscle Protein Synthesis

Why Leucine?

Chemical structure of the anabolic bcaa l-leucine.

Chemcial structure of the branched-chain amino acid l-leucine: Is this the key to muscle protein synthesis? (Source: Wikimedia.org : Public Domain Licence)

Leucine is an amino acid, a ‘building block’ of the human body – and the bodies of rats if you read all of the literature on the topic. It is commonly paired with Isoleucine and Valine. When paired with those other two amino acids it goes by the name ‘Branched Chain Amino Acids’. This cocktail can be enhanced further with Histidine, Lysine, Methionine, Phenylalanine and Threonine to make ‘Essential Amino Acids’. The common denominator in the two aforementioned supplements is Leucine and that will be the focus of this article.

Again, why Leucine?

The mammalian target of rapamaycin (mTOR) pathway integrates both intracellular and extracellular signals and serves as a central regulator of cell metabolism, proliferation, survival and if you lift… Growth [3]. This growth comes in the form of muscle protein synthesis (the process where the ‘building blocks’ you hear so much about actually become building blocks). However, for the mTOR pathway to do its thing and elicit muscle protein synthesis it needs stimulating. Leucine is that stimulation, this is the reason we need Leucine.

Prove it…

Gladly. Before I begin, for the rest of this article the phrases muscle protein synthesis and an increase in Lean Body Mass (LBM) will be used interchangeably as this is the outcome of successfully synthesised muscle protein.

Study: Muscle fractional synthesis rate (FSR) and net protein balance across legs: Subjects who received a leucine-enriched nutrient solution (EAA+CHO) by the end of the first hour post-exercise experienced a stronger protein synthesis rate. (Source: Dreyer et al. (2008))

Muscle fractional synthesis rate (FSR) and net protein balance across legs: Subjects who received a leucine-enriched nutrient solution (EAA+CHO) by the end of the first hour post-exercise experienced a stronger protein synthesis rate (A). Note the big difference in 2 hr post exercise net protein balance in subjects who received the leucine enriched solution in comparison to control subjects (B). (Source: Dreyer et al. (2008))

Walker et al. (2010) put 15 ‘moderately fit’ males through an 8-week resistance programme ad instructed the subjects to ingest 19.7g of Whey Protein and 6.2g of Leucine both one hour before and one hour after a training session [6]. After 8-weeks the group had increased their lean body mass and increased their overall strength. ‘But, they weren’t athletes, they were going to get stronger without supplements’. Good point, this study also had 15 ‘moderately fit’ males perform the same training with 112 kcal of Carbohydrates instead of Whey Protein and Leucine. They didn’t improve anyway near as much.

Dreyer et al. (2008) took 16 ‘untrained’ males and gave them 0.35g/kg LBM of Essential Amino Acids with 0.5g/kg LBM Carbohydrate mixture [1]. The other group received nothing. Muscle protein synthesis was found to be greater in the EAA group.

Koopman et al. (2000) also got his hands on 8 ‘untrained’ males and gave them a protein/carbohydrate mixture containing 16.6g Leucine [2]. This study is often paired with Dreyer’s work in Leucine-related literature as the structure and results of each study are so similar [1]. This suggests that it wasn’t just a one-off, Leucine seems to get results in general when it comes to the untrained. This study was also concluded with a statement saying that Leucine supplementation may even elicit greater gains in those who undergo a more vigorous training regime.

Moving on from the untrained. Schena et al. (1992) took 16 subjects on a 21-day trek to investigate the effects of BCAAs on a body undergoing hypoxic effects [4]. However, the results are interesting for those of us who reside a little closer to sea level. The mixture was 5.76g Leucine, 2.88g Isoleucine and 2.88g Valine (a 2:1:1 ratio quite common in BCAA mixes) and was administered to the BCAA group daily. An unfortunate placebo group also came on this trek. The BCAA group lost more body fat than the placebo group and even increased LBM. This was tested further by measuring arm and leg cross-sectional area after the trek in both groups. The BCAA group maintained (and in some cases increased) CSA however the placebo group lost up 6.8% of their CSA. The conclusion was that the BCAA group were somehow synthesising muscle on the trek whilst the placebo group were in catabolic state. The reason? You guessed it – the Leucine.

Eggs, a rich leucine source

While eggs may not be a good post-workout solution due to their high fat content, they’re quite high in leucine, too (Norton, LE., et al. (2012)) – and thus make a high quality protein source for everyday use (Photo credit: Pixabay.com / gsconsultit ; CC Licence)

A review has also been published by Stark et al. (2012) which evaluates the source and timings of protein consumption [5]. The first topic of discussion for them? Leucine. They summarised, to prevent over-complicating and over-calculating, that 3-4g Leucine should be consumed along a whey protein shake for maximum muscle protein synthesis. They also brought up a valid point which you may have picked up from my earlier evidence.

Leucine should be consumed with a fast-acting carbohydrate (e.g. dextrose, maltodextrin or waxy maize starch).

Simply put, Leucine cannot modulate protein synthesis as effectively without insulin. How do we increase the presence of insulin? Eat something sweet. Sucrose in water has been used in some Leucine articles so don’t feel guilty if you do consume something with a high GI.

How to apply this article to your daily training routine

  1. Put away your calculator. The 0.35g/kg LBM was what the researchers used to standardise the study and to ensure each subject definitely had enough Leucine. 3-4g is more than adequate, if you’re a slightly larger than average human or your scoop is 5g then that extra 1-2g will not do you any harm.
  2. Make sure it’s consumed with some Whey. Leucine may have stimulated the mTOR pathway but you still need some protein to synthesise. As Stark said, and Walker demonstrated, Leucine is best to be consumed to be consumed with Whey.
  3. High GI carbohydrates are you friend post training. This is another topic altogether so I won’t list all your possible ‘friends’ however fat-free milk, gummy bears and dextrose high foods are popular options.
  4. Immediate consumption isn’t necessary, you have time to drive home from the gym, shower and put your feet up. A lot of these studies had the subject consume their Leucine 45-60 minutes post-training and recorded the highest muscle protein synthesis 120 minutes after training.

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Picture sources: Ironphoto.de – Photography for Athletes

About the Author – Jonathan Kelly

Jonathan is a strength and conditioning coach working in professional rugby league in the UK. With a history of evidence based writing and an increasing library of published journal articles he enjoys translating written theoretical science into a practical environment, applying a ‘science versus reality’ approach to training, nutrition and supplementation.

The versatile nature of his job allows him work prescribe training across the whole exercise spectrum including strength training, bodybuilding, injury prevention and conditioning. To give his athlete’s the competitive edge he is also well versed in the prescription of effective and scientifically proven supplements.

References (Click to expand)

[1] Dreyer HC, Drummond MJ, Pennings B, Fujita S, Glynn EL, Chinkes DL, Dhanani S, Volpi E, and Rasmussen BB. Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle. Am J Physiol Endocrinol Metab 294: 392-400, 2008. URL: http://www.ncbi.nlm.nih.gov/pubmed/18056791.

[2] Koopman R, Wagenmakers AJ, Manders RJ, Zorenc AH, Senden JM, Gorselink M, Keizer HA, and van Loon LJ. Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects. Am J Physiol Endocrinol Metab 288: 645-653, 20051. URL: http://www.ncbi.nlm.nih.gov/pubmed/15562251.

[3] Laplante M and Sabatini DM. mTOR signaling at a glance. Journal of Cell Science 122: 3589-3594, 2009. URL: http://jcs.biologists.org/content/122/20/3589.full.

[4] Schena F, Guerrini F, Tregnaghi P, and Kayser B. Branched-chain amino acid supplementation during trekking at high altitude. The effects on loss of body mass, body composition, and muscle power. Eur J Appl Physiol Occup Physiol 65: 394-398, 1992. URL: http://www.ncbi.nlm.nih.gov/pubmed/1425642.

[5] Stark M, Lukaszuk J, Prawitz A, and Salacinski A. Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training. J Int Soc Sports Nutr 2012 9: ePub, 2012. URL: http://www.jissn.com/content/9/1/54.

[6] Walker TB, Smith J, Herrera M, Lebegue B, Pinchak A, and Fischer J. The influence of 8 weeks of whey-protein and leucine supplementation on physical and cognitive performance. Int J Sport Nutr Exerc Metab 20: 409-417, 2010. URL: http://www.ncbi.nlm.nih.gov/pubmed/20975109.


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