The Benefits of Leucine for Muscle Growth and Health

To promote optimal health, our bodies need a range of nutrients, many of which must come from the diet or supplements. Leucine is one example of this – which makes the benefits of leucine such an important topic.

First of all, leucine is one of three compounds called branched chain amino acids, or BCAAs. You may have heard the term before, as BCAAs are common in bodybuilding and for anyone wanting to develop muscles.

Of the three, leucine is the most significant for muscle synthesis and has been the subject of more research. In this post, we’re talking a look at the evidence that surrounds leucine, how it works and ways that you can take advantage of it.

Leucine, BCAAs and Muscle Growth

Leucine is classified as an essential amino acid. This means that you must get it in your diet – as the human body cannot produce it.

Like I mentioned before, it is also a BCAA, which refers to a specific amino acid structure. BCAAs are especially common in the muscles and they are also burned as fuel during exercise. In fact, BCAAs are the only amino acids treated in this way.

As a consequence, BCAA levels in the muscle and in the blood tend to be lower after exercise (1). This pattern means that BCAAs are critical and, of these, leucine is the most significant.

You will also sometimes see leucine called L-leucine, especially in supplements. The L- refers to a specific version of the amino acid.

Basically, many chemicals exist in two forms, known as enantiomers, which are mirror images of one another. For amino acids, the L- enantiomer is the biologically active form and many supplements will just include the L- variation for that reason.

Leucine and Muscle Development

With the prevalence of BCAAs in the muscle and their use as fuel, it’s no surprise that most discussions of leucine and BCAAs emphasize muscle development. Indeed, this is where the research has focused as well.

To begin with, leucine serves to activate a pathway called mTOR. This then activates muscle synthesis by promoting the activity of p70S6K (2,3,4).

In short, leucine promotes the synthesis of specific proteins, which then leads to muscle growth.

Research has confirmed this mechanism in humans (5,6,7) and resistance exercise can further increase muscle development outcomes (8).

The other two BCAAs can also improve muscle development but their effect is weaker (9,10). Indeed, studies show that supplementing just leucine has the same general impact on muscle development that a complete protein does.

One reason is that leucine plays two roles in muscle development.

First, it acts as a substrate, like the other BCAAs. This means that it is used like a building block to create the proteins that are needed.

In addition, leucine helps to up-regulate protein development. So, the presence of leucine means the whole process is more effective and faster. That action is something other compounds don’t do (11,12).

There are two implications to consider.

First, these patterns mean that leucine is critical to muscle development and maintenance. So, insufficient intake of the amino acid could result in impaired muscle synthesis and potentially muscle loss over time.

This also means that getting enough leucine could help prevent age related muscle loss, along with muscle loss due to disease or inactivity (13). Indeed, one study found that leucine was effective in older adults for muscle growth (14), suggesting that it may be a powerful tool for this age group.

Second, research shows that increasing leucine levels promotes muscle synthesis. This means that you are going to need higher amounts of leucine if you’re actively trying to build muscle (15). With that in mind, it’s no wonder so many people supplement leucine and/or BCAAs.

You can also find out more about the way leucine works in the video below, along with information about what you can expect when taking leucine. The site Examine.com also has a very detailed post on the science behind leucine and the precise mechanisms that occur.

Other Health Benefits of Leucine

While leucine is strongly associated with muscle development, there are some other areas to consider.

Life Length

One topic is longevity, where leucine plays an indirect role. For example, leucine may be a key reason why dairy proteins can help to increase the lifespan (16,17,18).

Leucine does also promote muscle synthesis and there is an association between muscles and longevity.

For that matter, having sufficient muscle mass is connected to a range of other health benefits, many of which can contribute to life length. In contrast, people with a higher percentage of body fat compared to muscle mass are at increased risk of many conditions, including heart disease and diabetes (19,20,21).

This is true regardless of how fat or thin a person is (22,23). So then, increasing muscle mass can lower disease risk and potentially increase longevity – and leucine is one compound that can help with this goal.

Weight Loss

Leucine is also relevant to weight loss. Once again, this effect is partly connected to muscle development. For example, lean muscle does help to improve metabolism (slightly), which can make weight loss easier (24,25). Leucine itself also increases the metabolism directly (26).

At the same time, high protein diets strongly contribute to weight loss. This works because protein is satiating, making people feel less hungry. As a result, many people naturally eat less on a high protein diet. Leucine is one part of such a diet, especially if you’re relying on animal-based protein sources.

Research has also shown that high protein diets that contain around 10 grams of leucine per day contribute to better weight and fat loss overall. Those same diets also make it easier to maintain lean body mass (27).

Leucine is also relevant to weight loss in a different way. Specifically, it helps to prevent the loss of muscle along with fat (28). This is a critical outcome because many people do end up losing muscle along the way, which can be detrimental for health and certainly isn’t desirable.

Other Health Outcomes

There are also some other health benefits of leucine, although these have been studied less. For example, there are some indications that leucine can help improve blood sugar control and lower the levels of LDL cholesterol (29).

The way that leucine can promote both weight loss and muscle development also creates the potential for many indirect benefits – as both of those outcomes are powerful for health.

With so many different studies on leucine, there is no consensus about how much you should be taking. Instead, doses vary from around 2,000 mg to 5,000 mg (2 grams to 5 grams).

How much you need may also vary depending on how you are taking the leucine, the amount of exercise that you do and your protein intake.

Anything from around 2,500 mg and up should be enough to promote muscle synthesis in most situations (30). But, if you’re very active or trying to gain a significant amount of muscle, you may want to use a higher dose.

In most cases, people either supplement when they are fasted or with a relatively low protein meal. Research also suggests that preloading leucine before a workout can lead to more muscle protein synthesis advantages than using it at other times (31,32).

While leucine can be taken in supplement form, either on its own or with other BCAAs, there are also natural sources.

In particular, leucine is present in any protein that naturally contains all amino acids. Animal-sourced protein is the best option for this, which includes red meat and dairy. This is one reason why diets heavy in animal products often work well for muscle development.

However, the single best source of leucine is whey protein, which contains around 10% leucine by weight. As a result, whey protein powder works extremely well as a source of leucine and for muscle building overall.

The brand below is one high-quality example and you can also look at my list of best grass fed whey protein powder brands for more options.

And, of course, there are also various supplements currently on the market. For example, you can get leucine as a powder, such as in the image below or you can get various BCAA supplements, which contain all three BCAAs.

On a side note – leucine will only help with muscle development if you are already getting enough protein in your diet. This is another key reason why whey protein powder can work so well, as you have everything you need all in one place.

Final Thoughts

Leucine is a critical compound for health – and it isn’t just relevant to bodybuilders. Instead, the amino acid helps people to develop and maintain a positive body composition, while reducing the risk of muscle loss. Plus, it does offer other health benefits, including advantages for weight loss and longevity.

Whey protein powder is the most powerful way to get those outcomes, especially as it offers so many other benefits.

This powder also works perfectly for weight loss because you can make a protein shake or smoothie to replace one of your meals each day. Many people do so for breakfast and you can also add in extra nutrients, such as from greens (like kale) and berries.

For example, Dr. Axe offers a great roundup of protein smoothies, which makes a powerful starting point.

You can even make smoothie bowls if you wanted to or just add your protein powder to coffee. For that matter, the site Minimalist Baker offers a 5-minute smoothie bowl recipe, along with the details you need for getting the right consistency each time.

What about you? If you were going to get more leucine or BCAAs in your diet, how would you go about it?​

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