Leucine is one of three branched chain amino acids, along isoleucine and valine. Studies suggest that of all three, leucine is the primary and most potent activator of muscle protein synthesis. Cells are able to sense leucine and respond by stimulating protein synthesis via the enzyme protein mammalian target of rapamycin (mTOR), a master-regulator of protein synthesis. Although leucine is the most anabolic studies suggest that all branched chain amino acids are needed to sufficiently activate muscle protein synthesis. We’re going to talk more about leucine benefits, how it works, and what the studies say.
L-leucine is an essential amino acid and recognized as one of three branched chain amino acids. Essential amino acids are considered “essential” as they are not synthesized on their own, therefore it is essential to obtain them from food or supplements.
Leucine along with valine and isoleucine conduct what is called intramuscular signaling.
While the majority of essential amino acids are oxidized within the liver, BCAAs and leucine are predominantly oxidized within the skeletal muscle and other peripheral tissues. The anabolic or muscle building effects of high-intensity training and resistance training are controlled through the changes in signal transduction, which control and facilitate muscle protein synthesis (the process of building muscle mass).
The signaling networks that controls muscle protein synthesis through translation involve the phosphorylation of the mammalian target of rapamycin (mTOR). Leucine has a definite consequence on this particular process and signaling pathway, therefore creating an anabolic effect on protein metabolism, increasing the rate of protein synthesis and decreasing the rate of protein degradation.
This creates an effect called a positive amino acid balance, which is essential for increasing muscle size and strength.
Leucine in particular, is vital in this process of building muscle mass and indirectly activates the p70 s6 Kinase and the eIF4F Complex, which is essential for the anabolic effects of muscle tissue and recovery.
The human body utilizes essential amino acids for fuel while your workout. When your body is low on essential amino acids, it reduces the rate of protein synthesis and catabolizes muscle tissue, and your body cannot adequately repair itself. When you’re training at a high-intensity and you’ve burned through those BCAA stores, your body starts to be catabolic or starts to break down muscle mass for fuel instead. By supplementing with essential amino acids you ensure your body is in a positive balance, to help promote muscle growth, repair, and reduce muscle soreness after your workout.
First and foremost, leucine helps stimulate muscle protein synthesis. This is substantially proven and well established in studies utilizing elderly patients.
As we age, we experience a phenomenon called anabolic resistance. This is when cells become more resistant to flipping on the switch for muscle protein synthesis. Anabolic resistance can be partly ameliorated with supplemental leucine, as research indicates that older adults need twice as much leucine compared to younger adults for similar activation of MPS [R].
This phenomenon can be partially explained, by the increased retention of orally ingested leucine in the gut, which is twice the amount retained to young adults [R].
Studies suggest that supplementing leucine alone, however, does not induce greater anabolic changes to supplementing all branched chain amino acids, essential amino acids, or protein.
Supplements marketing a higher ratio of leucine above a 2:1:1 will have no greater effect on muscle protein synthesis.
In a randomized, double-blind, placebo-controlled study conducted at Baylor University, 30 were administered BCAA, Leucine, or placebo. The supplements were consumed in three equal doses pre, immediately before resistance training, and post workout. The results indicated that both leucine and BCAA supplementation led to greater levels of phosphorylated 4E-BP1 and cell signaling of the mTOR pathway, a serine/threonine kinase which stimulates protein synthesis through amino acid activation. These findings suggest that the other two BCAAs [isoleucine and valine] may contribute to greater activation rates than leucine alone [R]. Furthermore, the study concluded that supplementing BCAAs had greater effects on mTOR than taking greater amounts of leucine alone.
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A positive net amino acid balance and increase in muscle protein synthesis is also achieved by the inhibition of protein breakdown. Inhibiting muscle breakdown will result in faster recovery times and less exercise induced muscle soreness.
Resistance training and lifting weights causes micro tears in your muscle fibers, which leads to muscle soreness. Soreness can interrupt your regularly scheduled programming and have a dramatic impact on peak power, strength, and rep volume.
A study published in the Journal Nutrients, examined the effects of BCAA supplementation on recovery from resistance training. Using a randomized, double-blind, placebo-controlled research design, participants were enrolled into either a BCAA or placebo group. At 72 hours post workout, the BCAA group reported significant less muscle soreness than the placebo group.
Again, leucine supplementation is more effective when all essential amino acids, or branched chain amino acids are supplemented together.
A study conducted at the University of Illinois, found that leucine is essential to enhance or amplify the signal for protein synthesis at the level of peptide initiation. However, ingestion of all amino acids, as opposed to leucine alone initiates muscle recovery at a faster rate [R].
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Numerous studies have found that dietary leucine supplementation can aid in weight loss. Counting macronutrients as a major weight loss protocol is starting to become more and more prevalent. Higher protein intakes with lower carbohydrate and fat intake are associated with greater reduction of weight loss.
The mechanism is likely due to increased energy expenditure caused by improved energy efficiency. Although most research come from animal studies, more evidence is needed through human clinical trials to replicate these results [R].
Animal studies have suggested that leucine may improve human growth hormone resistance. Human growth hormone reduces as we age due to anabolic resistance and your pituitary gland reduces the amount of human growth hormone it produces.
Preliminary results show that prolonged leucine supplementation improves growth hormone levels, by promoting IGF-1, reducing IGF-1 degradation, and facilitating growth hormone resistance synthesis in the liver, as well muscle protein synthesis by regulating mTOR anabolic signaling transduction [R].
More research is needed to confirm these results and use of leucine as a potential therapeutic to increase HGH.
Leucine is a powerful essential amino acid, and a pivotal signaling molecule in the synthesis of protein. Studies suggest that the most effective way to utilize luecine is by supplementing protein, essential amino acids (EAA), or branched chain amino acids (BCAA). Leucine plays a role in intramuscular signaling, yet is co-dependent on other amino acids, to facilitate muscle growth and recovery.
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