Leucine is one of three branched-chain amino acids, along with isoleucine and valine. Studies show that leucine is the primary and most effective stimulator of muscle protein synthesis out of the three. Cells are able to sense leucine and respond by stimulating protein synthesis via the mammalian target protein enzyme rapamycin (mTOR), a master regulator of protein synthesis. Although leucine is the most anabolic of all studies, all of the branched-chain amino acids are required to adequately activate muscle protein synthesis. We’ll talk more about the benefits of leucine, how it works, and what the studies say.
What is L-Leucine?
L-leucine is an essential amino acid and is recognized as one of three branched-chain amino acids. Essential amino acids are considered “essential” in that they are not made on their own, so it is essential to obtain them from food or supplements.
How does L-Leucine work?
Leucine, along with valine and isoleucine, conduct what is called a muscle signal.
While the majority of essential amino acids are oxidized within the liver, BCAAs and leucine are mostly oxidized within skeletal muscle and other peripheral tissues. The anabolic or muscle-building effects of high-intensity training and resistance training are controlled by changes in signal transduction, which control and facilitate muscle protein synthesis (the process of building muscle mass).
Signaling networks that control muscle protein synthesis through translation include phosphorylation of the mammalian target of rapamycin (mTOR). Lysine has a specific consequence on this process and signaling pathway, thus creating an anabolic effect on protein metabolism, increasing the rate of protein synthesis and decreasing the rate of protein degradation.
This results in an effect called positive amino acid balance, which is essential for increasing muscle size and strength.
Leucine in particular is vital in the process of building muscle mass and indirectly activates p70 s6 kinase and the eIF4F complex, which is essential for muscle tissue anabolic effects and recovery.
The human body uses essential amino acids for fuel during exercise. When your body is low in essential amino acids, it reduces the rate of protein synthesis and breaks down muscle tissue, and your body cannot adequately repair itself. When you train at a high intensity and burn through your BCAA stores, your body starts catabolic or starts breaking down muscle mass for energy instead. By supplementing with essential amino acids, you ensure that your body is in positive balance, to help promote muscle growth, repair, and reduce muscle soreness after exercise.
1. Stimulation of muscle protein synthesis
First and foremost, leucine helps stimulate muscle protein synthesis. This has been largely and well proven in studies using elderly patients.
As we age, we experience a phenomenon called anabolic resistance. This happens when cells become more resistant to hitting the muscle protein synthesis switch. Anabolic resistance can be partially improved with supplemental leucine, as research indicates that older adults require twice as much leucine than younger adults for similar activation of MPS [R].
This phenomenon may be explained, in part, by the increased retention of orally ingested leucine in the gut, which is twice the amount retained in young adults. [R].
Studies show that leucine supplementation alone, however, does not result in greater anabolic changes to supplement all branched-chain amino acids, essential amino acids, or protein.
Supplements marketing a higher percentage of leucine than a 2:1:1 ratio will not have a greater effect on muscle protein synthesis.
In a randomized, double-blind, placebo-controlled study conducted at Baylor University, 30 were given BCAA, Leucine, or a placebo. The supplement was consumed in three equal doses before resistance training and immediately after exercise. Results indicated that leucine and BCAA supplementation led to higher levels of 4E-BP1 phosphorylation and cell signaling of the mTOR pathway, a serine/threonine kinase that stimulates protein synthesis through amino acid activation. These results indicate that the other two types of branched-chain amino acids [isoleucine and valine] It may contribute to greater activation rates than leucine alone [R]. Furthermore, the study concluded that BCAAs supplementation has greater effects on mTOR than higher intakes of leucine alone.
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2. It prevents the breakdown of muscle mass
A net positive amino acid balance and increase in muscle protein synthesis is also achieved by inhibiting protein breakdown. Inhibiting muscle breakdown will lead to faster recovery times and less exercise-induced muscle soreness.
Resistance training and weight lifting cause micro-tears in the muscle fibers, resulting in muscle soreness. Pain can interrupt your regularly scheduled programs and have a significant impact on peak strength, power, 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 in either the BCAA group or the placebo group. At 72 hours post-workout, the BCAA group reported significantly less muscle soreness than the placebo group.
Again, leucine supplements are most effective when all of the essential amino acids, or branched-chain amino acids, are supplemented together.
A study conducted at the University of Illinois found that leucine is essential for enhancing or amplifying the protein synthesis signal at the level of initiation peptide. However, taking all of the amino acids, as opposed to leucine alone, initiates muscle recovery at a faster rate [R].
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3. It helps in losing weight
Several studies have found that leucine supplements can help with weight loss. Counting macronutrients as a key weight loss protocol is starting to become more and more popular. Higher protein intake and lower carbohydrate and fat intake are associated with greater weight loss reduction.
The mechanism is likely due to increased energy expenditure resulting from improved energy efficiency. Although most of the research comes from animal studies, more evidence through human clinical trials is needed to replicate these findings. [R].
4. May Increase Human Growth Hormone (HGH)
Animal studies have indicated that leucine may improve human growth hormone resistance. Human growth hormone decreases as we age due to anabolic resistance and the pituitary gland reduces the amount of human growth hormone it produces.
Preliminary results show that prolonged leucine supplementation improves growth hormone levels, by enhancing IGF-1, decreasing IGF-1 degradation, facilitating growth hormone resistance synthesis in the liver, as well as muscle protein synthesis by regulating mTOR anabolic signal transduction. [R].
More research is needed to confirm these findings and the use of leucine as a potential treatment for increasing growth hormone.
Leucine is a powerful essential amino acid and a pivotal signaling molecule in protein synthesis. Studies show that the most effective way to use leucine is with a protein, essential amino acid (EAA) or branched chain amino acid (BCAA) supplement. Leucine plays a role in muscle signaling, but is co-dependent on other amino acids, to facilitate muscle growth and recovery.
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