​The Effects of Leucine on Protein Synthesis and Muscle Growth

​The Effects of Leucine on Protein Synthesis and Muscle Growth

Posted by Leah Arrowsmith on 9th Jul 2018

What is Leucine?

Leucine is a BCAA (branched-chain amino acid) which plays a pivotal role in regulating muscular health. Found in whey protein, this compound is believed to give whey protein its ability to be able to assist with muscle growth (1). In total, there are three BCCAs and 9 amino acids. Branched-chain amino acids differ from essential amino acids as the enzymes of the liver do not break them down, which allows them to quickly and easily enter the tissues of the body. As soon as leucine enters the body, it will begin to modulate insulin sensitivity, break down body fat, and stimulate the growth of muscles. Leucine is also able to augment MPS.

Leucine and protein synthesis

When trying to build or preserve muscle tissue, maximizing the stimulation of protein synthesis is vital. Many people already understand that consuming high protein foods leads to an increase in protein synthesis in the muscles. This is one of the main reasons as to why protein supplements are so popular post-exercise. Studies have shown that high blood levels of amino acids directly correlate with an increase in muscle protein synthesis. Of all the amino acids, leucine has been shown to possess the strongest effects on protein synthesis.

Leucine is also known to have anti-wasting properties, and when the levels of leucine remain consistent, it is actively able to provide a preserving effect on muscle mass (2). This makes it ideal for situations where muscular atrophy may occur, especially when the individual consumes a dose-dependent supplement. It is believed that leucine works by saturating the protein-degradation cells of the muscle (3), therefore, slowing the rate of muscle wasting.

Leucine and muscle building

Leucine works on muscle growth by activating a compound known as mammalian target of rapamycin (mTOR). A good way to look at mTOR is to view it as a switch that can be turned on to manufacturer muscle protein. Leucine not only helps lay down the foundations for protein synthesis, but it also plays a pivotal role when it comes to upregulating. Even when you have more than enough amino acids in your system to help with building muscle, leucine gets to work by augmenting the rate of protein synthesis to the next level.

Leucine and Fat Loss

The last body fat that you have, the more pronounced your muscles will be. For many, reaching their target body fat levels whilst holding on to their muscle mass can be a challenge at the best of times. Many Studies have proven the effects of high protein intake for preserving muscle tissue during dieting. Research conducted at the University of Illinois delved deeper into the effects of leucine during dieting. Participants were given a diet plan that consisted of 125 grams of protein each day, with 2.5 grams of leucine to be consumed per meal. The total amount of leucine each day totalled 10 grams.

Of the two study groups, those that consumed diets with high levels of leucine experienced greater fat and weight loss and we're better able to preserve their lean body mass. The high leucine diet group also had better control of glucose levels in the body. In a separate study at Columbia University, scientists fed rats a high-fat diet. When the rats were supplemented with leucine, they experienced a 25% decrease of body fat weight. The leucine supplement also had a direct effect on reducing the LDL cholesterol and boosted that resting metabolic rate.

How Much Leucine to Take

While there is no set data on the perfect amount of leucine to consume on a daily basis, past studies looking at single doses of 2.5 g showed it to stimulate protein synthesis. Longer-term studies looked at an intake of 10 grams a day, split into 2.5-gram doses over four meals were found to provide the most beneficial effects. The majority of people receive their leucine intake from whey protein supplements, which contain approximately 10 grams of leucine per 100 g of whey protein. This means that for optimal leucine intake, a 25-gram whey protein shake will contain 2.5 g of leucine.

When you combine leucines effects on being able to stimulate muscle growth, build new muscle tissue, and assist with burning body fat, it becomes clear as to why it is one of the most important branched-chain amino acids in the body.


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