The Strongest Amino Acid Supplement for Muscle Growth – L-leucine!

We may receive commissions on qualifying purchases made from some of the links on this post.

Top Picks

Some people may not realize it, but there is a science to bodybuilding. Physical activity is perhaps the most significant aspect to it, but your body’s chemical makeup and dietary needs can affect your muscle growth.

Although there are many supplements that can enhance your training, yet one deserves special attention: L-leucine.

This could be one of the most important nutrients for both mass gains and preservation. Supplementing with it could dramatically change how you workout.

This guide will explain what it is, how it works, the benefits and side effects, plus the top l-leucine products on the market.

The Best L-Leucine Supplements

Below are what we believe to be the top-rated l-leucine supplements currently on the market.

1. BulkSupplements Pure L-Leucine Powder

If you are looking for a pure product, I feel this offering from BulkSupplements could fit the bill.

Containing nothing but 100 percent l-leucine in a powder form, this supplement boasts no fillers or flavors. It’s also gluten, soy, dairy and free from known allergens, which might suit those with intolerances.

A suggested dose of 2500 mg should make this 500-gram pack last 200 servings. I think is quantity great for those who want to pile on the serious muscle—frequent re-ordering shouldn’t be such an issue.

It’s also presented in a zip foil pouch which ensures the product remains as fresh as possible. What’s more, it’s third-party tested to back up its quality and purity.

  • No filler ingredients.
  • Respected manufacturer.
  • Free of sugar, gluten, and allergens.
  • Third party tested.
  • 200 servings.
  • Some users found the taste unpleasant.
  • It doesn’t mix well.

2. Nutricost Pure L-Leucine Powder

Much stronger than my first choice, this supplement gives you 5 grams of pure l-leucine with each serving.

I like the fact that this l-leucine formulation has been instantized. This means that when prepared it should dissolve better—clumping could possibly be avoided.

Each tub contains 100 servings. It’s independently tested and contains no fillers, GMOs or allergens.

  • No filler ingredients.
  • High dose of l-leucine per serving.
  • Third-party tested.
  • Made in the USA.
  • It leaves an unpleasant bitter aftertaste.
  • A lower number of servings than others reviewed.

3. Instantized L-Leucine by Muscle Feast

I would suggest this l-leucine supplement could be suitable for those who train for competition. Each serving contains 2500 mg of pure L-leucine powder—a solid dose for those looking to gain or retain.

Like the others on this list, this product is free of allergens and fillers. However, it takes it a step further by being HPLC (high-performance liquid chromatography) certified.

Furthermore, it’s ingredients are approved by WADA (World Anti-doping Agency), which means you should be able to compete with confidence.

This product contains 80 servings.

  • HPLC certified.
  • No filler ingredients.
  • WADA approved formulation.
  • Both in-house and independently tested for purity.
  • No allergens, irritants or artificial additives.
  • Sufficient dose per serving.
  • Despite the instantized form, some users found it difficult to mix.
  • Low volume in the container.

4. NutraBio 100% Pure L-Leucine

In my opinion, this product could be ideal for those people looking for convenience or an alternative to powder. The reason being, this supplement comes in capsule form.

Each pill contains 400 mg of l-leucine with a total serving (four capsules) of 1600 mg. As its a light dosage, I think could be suited towards the newcomer to muscle building.

Each tub contains 240 caps (60 servings). It’s HPLC certified for strength and quality, plus it’s manufactured in accordance with GMP and FDA standards.

  • The convenience of capsule form.
  • A mild alternative—great for those starting out in supplementation.
  • HPLC certified.
  • Suitable for vegans.
  • Non-GMO and gluten-free.
  • Four capsules per serving could be an overkill.

Informational guide to L-Leucine Supplements

What Is L-Leucine?

Protein is what your muscles are made of. Your body utilizes it to build and repair tissue, which is why it’s so important for muscle growth. Protein itself is a product of amino acids; without them, muscle would be non-existent.

There are 20 amino acids in total, and of those, nine are considered essential—your body cannot produce them, so you need to obtain it through exogenous means—via diet or supplementation.

L-leucine is an essential amino acid. Alongside valine and isoleucine, it makes up the trio referred to as branched-chain-amino acids (BCAAs). Out of the three l-leucine is considered the strongest and most influential.

The Benefits of L-Leucine

Here’s how l-leucine works and the advantages on offer for performance and training.

Builds Muscle

L-leucine amino acid joins ranks with insulin signaling pathways to activate protein synthesis—the process of muscle growth. It’s believed to be one of the key amino acids in muscle building.

Numerous studies have investigated its positive effects on muscular hypertrophy.

One theory is, l-leucine can encourage insulin production by preventing other elements which may slow it down. This hormone, known for regulating blood sugar levels also influences muscle growth.

Insulin Signaling for Muscle Building

Insulin signaling can have a positive impact on your workout too. Dysfunction in this process will not only reduce your muscle mass but also your skeletal muscle function. Consequences of this include limited movement and weakened muscles.

With resistance training, the tension placed on your muscle fibers causes microscopic tears in their form. An immune response regenerates the structure of your muscles, and this compensation is what adds to muscle mass.

Your muscle fibers are also lined with insulin receptors. If your insulin signaling process malfunctions, your muscles will deteriorate and weaken over time. This causes many health problems, particularly in the elderly, but to bodybuilders, it means that you won’t be able to develop your muscles effectively.

Preserves Muscle

When trying to cut, you are at threat of losing both body fat and lean muscle. To prevent your body from falling into catabolism (breaking down mode) you need protein—amino acids are the building blocks of this nutrient.

A serving of 1.8 grams of l-leucine is enough to encourage anabolic (building) actions in the body.

Enhances Recovery

Research shows that BCAAs prevent muscle soreness after physical activity.

Findings explain that thanks to protein synthesis, BCAAs displayed positive results in preventing muscle protein breakdown during exercise. This means it can speed up your recovery time, strengthening and building your muscles faster.

Boosts Strength

When you build-up stamina and mass, strength gains tend to follow. There are two significant studies to support this.

Firstly, experts put athletes to the test—six weeks of l-leucine supplementation raised power and endurance levels. Other research indicates that in only 12 weeks, strength improvements increased by almost 41 percent.

Assists Fat Loss

There is evidence that l-leucine supplementation speeds up fat loss. Another study found that it has the capacity to reduce the effects of age-related weight gain, and diet-related obesity.

L-Leucine and Diet

If you are looking to up your l-leucine amino acid intake, there are numerous foods which contain this amino acid.

Foods containing protein will usually include l-leucine, although concentrations will vary. Popular l-leucine-rich sources include:

  • Eggs.
  • Meat (game, beef).
  • Poultry.
  • Fish (cod, tuna).
  • Cottage cheese.
  • Milk.

Top vegetarian options are:

  • Spirulina.
  • Watercress
  • Alfalfa seeds
  • Kidney beans
  • Tofu.

How Much and When to Take L-Leucine

For the average adult, the recommended daily intake of l-leucine is set at 14 mg per kilogram (6.36 mg per pound).

For example, if you weighed 168 pounds your daily requirement would be 1068 mg.

However, this guideline is for regular dietary purposes—not your mass gaining needs.

The general opinion suggests from 1.5 to 5 grams depending on your goals.

When to Take L-leucine?

L-leucine amino acid can be supplemented as a standalone, or as part of BCAAs.

Here are some typical timing scenarios:

  • Leucine before bed—is an ideal opportunity to use your body’s regeneration process to boost post-workout recovery.
  • Throughout the day—will ensure your amino acids and therefore protein levels are kept at the optimum.
  • Post-workout—take within half an hour of the end of your session to aid recovery.
  • Pre-workout—around 30 minutes before training is a good window of opportunity.

The best time to supplement would be according to your goals, however, studies suggest the best time not to take l-leucine is with a meal.

Risks and Side Effects of L-Leucine

Consuming l-leucine through regular foods in your diet is generally considered safe. However, when supplementing, studies have shown excessive doses (above 500 mg per kilo of body weight) have increased ammonia levels within the body.

Other potential side effects include:

  • Digestive issues (nausea, bloating and diarrhea).
  • Fatigue.
  • Headaches.

L-leucine or BCAA supplements are generally not suitable for:

  • Pregnant or breastfeeding women.
  • Those who have maple syrup urine disease (MSUD)
  • Children.
  • Diabetics.
  • Anyone having surgery (use should be discontinued at least two weeks prior)

Remember to read the labels of any supplements or medications that you take.


If you’re looking to enhance your muscular gains, I believe l-leucine is one supplement worthy of consideration. It’s the most potent and sought after BCAA and so pure l-leucine amino acid is all the rage in muscle growth.

My top choice is BulkSupplement’s pure l-leucine powder. It’s effective without being overpowering and contains no unnecessary ingredients.