Last updated: August 24, 2021

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The amino acid L-leucine can help you build muscle, get enough protein during your diet and generally improve your performance. Leucine also has a positive effect on the body's energy production, is one of the ketogenic amino acids and thus inhibits the breakdown of glucose in the body.

In our L-Leucine test 2022 we present all the L-Leucine products we have tested in detail. We explain the different types, the advantages and disadvantages and much more about L-Leucine. In addition, you will find many tips and tricks in this article that can help you to buy the right L-Leucine for you.


  • L-leucine belongs to the 3 BCAA amino acids together with isoleucine and valine, which consist of a branched hydrocarbon chain. They are not produced in the body, but are ingested with food.
  • Leucine prevents the breakdown of proteins in the body after exercise, which has a positive effect on muscle maintenance and results in an optimised protein balance.
  • A lack of leucine is rather rare. Under certain circumstances, however, the supply of leucine can be disturbed.

The Best L-Leucine: Our Picks

Advice: Questions you should ask yourself before buying L-Leucine

In this first section we will tell you about the effectiveness of L-Leucine, all the important information about it and the current state of scientific studies.

What is L-Leucine?

L-leucine is one of the 9 essential amino acids and one of the three branched-chain amino acids, also known as BCAAs (Branch-Chain Amino Acids). Since leucine cannot be produced by the body, you need to take it through food or appropriate supplements.

Leucine is responsible for the synthesis of protein structures and especially for building muscle mass. It is involved in building new tissues, especially protein metabolism in the muscles and liver. At the same time, leucine promotes healing processes.

shirtless muscular african american sportsman doing push ups with dumbbells at gym

L-leucine is taken when muscles and muscle tissue need to be increased. L-leucine capsules or powder are often taken with a fitness goal.
( / lightfieldstudios )

Foods with a high leucine content are especially animal products such as beef, chicken eggs or salmon. Walnuts and wholemeal products also supply the body with the amino acid, but only contain smaller amounts.

Why is L-leucine relevant for muscle building?

The amino acid leucine has many properties that have a positive effect on protein synthesis, which is why it is important for muscle building. After athletic exertion, the body can form an increased breakdown of proteins, which could have a negative effect on the whole organism. The role of leucine is to prevent this breakdown and thereby balance the protein level.(1)

Leucine is a ketogenic amino acid and ensures the body's positive energy production. During or after intensive training sessions, it inhibits glucose breakdown in the body, so that a sustained increase in performance can be expected with sufficient leucine intake. During extreme athletic exertion, free leucine is activated for energy production.(2)

What are the effects and side effects of L-leucine?

The amino acid is of great importance for the human metabolism. The human body has a daily L-leucine requirement of about 1.2 grams. L-leucine builds muscle and muscle tissue. A high L-leucine dosage can counteract muscle atrophy later on.

Anyone who has problems with their muscles or needs to build muscles should take L-leucine. Leucine increases energy supply and muscle protein synthesis after training. After a training session, leucine acts on protein formation by activating certain key enzymes.(7)

L-Leucine can support you during your diet and thus cover your daily needs. It has a positive influence on the release of hormones that affect satiety. In addition, the muscle-building effect of L-leucine was comparable to the intake of protein supplements such as whey concentrate, hydrolysate or soy protein concentrate.(5)

During dieting, the energy deficit causes not only a decrease in fat tissue but also a loss of muscle. Scientists investigated whether leucine supplementation can counteract this effect in rats that received only half of their energy requirement over a period of 6 weeks. At the end, the researchers measured higher protein concentrations in the liver and higher RNA concentrations in the muscles of the leucine group.(6)

Another positive effect of L-leucine is its therapeutic power in liver diseases. Patients who suffered hepatic encephalopathy as a result of liver cirrhosis were studied and after a regulated intake of BCAA their situation and symptoms improved significantly. (4)

Some people naturally have an excess or deficiency of certain substances. Leucine can inhibit or stop the transport of other amino acids into the brain, so it influences the composition of messenger substances.

Area of application Description
Weight loss Due to its positive effect on the growth hormone somatotropin (STH), which promotes length growth at a young age and regulates the relationship between muscle mass and body fat in adulthood, leucine can be used to accompany diets designed to promote weight loss
Diabetes Since leucine promotes the release of insulin, it can be used to treat diabetics.
Liver disease Leucine promotes protein synthesis in liver and muscle cells. For a better energy supply, as well as to promote wound healing, leucine can therefore be administered in liver diseases
Muscle building Leucine is needed for the energy supply of the muscles. At the same time, leucine prevents the breakdown of muscle tissue and thus helps to maintain and build muscle tissue

Leucine is well tolerated in fortified foods and supplements, even in doses that far exceed the recommended daily allowance (RDA).

For whom is L-leucine intake suitable?

The use of L-leucine is very diverse. Among other things, you can take it during the training phase to build muscle, as a support during a diet and also in a vegetarian or vegan diet.

L-Leucine is mainly found in meat and dairy products. Vegans do not eat meat and dairy products, which leads to an L-Leucine deficiency. The L-Leucine amino acids sold are made from plant-based ingredients and are ideal for vegetarian and vegan diets.

The BCAAs are particularly popular with athletes in the field of fitness and muscle training or bodybuilding and significantly improve endurance training. Together with isoleucine and valine, leucine belongs to the BCCA amino acids, which are responsible for muscle building. You can take L-leucine in powder or in capsules if you constantly go to the gym and want to build up your muscles faster.

What is the recommended dose of L-Leucine?

It is recommended to take L-leucine in a natural dose, i.e. in food leucine comes in a bound form. In general, a daily dose of between 10 and 50 mg of leucine per kg of body weight is recommended. There are hardly any risks with an excess intake, but nevertheless at a dose of 35 g per day can be metabolised.(3)

Multicolored tablets on white background

Leucine is sold in capsules or as a natural powder.
( / ulleo)

In combination with a balanced diet and appropriate training, you can take up to 4 grams of L-Leucine. This dose helps build muscle and strength, increases endurance and strengthens the immune system.

What is the alternative to L-Leucine?

L-leucine is one of the amino acids and is related to isoleucine and valine, also known as BCCA. Your body cannot produce these three amino acids itself. So you have to take them with your food.

Theoretically, you can't do without any of the three acids, as each is found in certain foods. BCAAs are the only amino acids that are not converted in the liver. This makes them directly available to muscle tissue, where they exert a positive effect in many ways.

Besides L-leucine, there is another essential amino acid with almost identical biochemical properties: isoleucine.BCAAs are also often offered as a trio in food supplements.
In the medical field, the amino acid leucine is a component of reconstructive infusion solutions.

Decision part: L-leucine powder or leucine capsules?

As already mentioned above, you get L-leucine through a balanced diet. In addition, it is possible to take L-leucine in capsules or as a powder.

What distinguishes leucine powder and what are its advantages and disadvantages?

L-leucine powder and L-leucine capsules are identical, only their chemical form differs. Compared to capsules, the powder is cheap in price. If you are price-conscious and have a limited budget, powdered L-leucine is the cheaper option.

The powder does have one disadvantage with regard to ingestion. The powder often dissolves poorly in water and therefore has an unpleasant texture when consumed.

  • Inexpensive
  • Different flavours
  • Difficult to dissolve in water
  • Impractical dosage

What are the advantages and disadvantages of leucine capsules?

Capsules are easier to take. Taking them is uncomplicated: just the capsule and some water. The capsule dissolves in the stomach and the active ingredient is metabolised. In addition, you know the dosage in capsules beforehand.

The disadvantage of capsules compared to powder is the higher price.

  • Easy dosage
  • transportability
  • neutral taste
  • More expensive than powder

Buying criteria: Use these factors to compare and evaluate L-Leucine

If you are faced with the choice between L-Leucine capsules or powder, we have prepared the most important buying criteria to guide you in your purchase.

In the following, we would like to show you which factors you can use to compare and evaluate L-Leucine products. Afterwards, it will be easier for you to decide on a specific product.

Purpose of use

The use of an L-Leucine product depends on the daily intake. If you need L-Leucine for your fitness training, you should rather take capsules, as they are easier to take.

If you prefer L-Leucine as a powder, you must always have a cup, water and something to mix it with.

Package size and dosage

The package size and dosage vary depending on the product type and price.

Depending on the recommendation, there are between 30 and 100 servings. You can usually find the recommended dosage on the back of the product.

L-Leucine powders are usually available in 350, 500 or 1000 gram packs. For easy dosing, a measuring spoon, a so-called scoop, is usually included.

Training intensity Daily dose for both sexes
Training-free days 1 g
Training days 2-3 g
Intensive training Increase by up to 0.1g/kg body weight, max. 10 g single dose

The same applies to the capsules. They can be found in different sizes. Usually, packs of 100 or 240 capsules are offered. Some sports retailers or online shops sell smaller packs, e.g. 60 capsules.


L-leucine products are ideal for bodylbuilders and strength athletes in muscle-building phases.

Pure L-leucine powder is usually vegetarian and can be combined with protein shakes.

L-leucine can be taken in a mixture with the other two amino acids of BCAA or pure. Pure L-leucine is usually only available as a powder.

In numerous BCAA supplements and in many other products containing BCAAs, leucine is usually added in a higher proportion than the other BCAAs. For example, ratios of 2:1:1 or 3:1:1 are the rule, but nowadays 8:1:1 (leucine : isoleucine : valine) mixtures are also offered.

Did you know that timing is important when taking amino acids because protein synthesis in the muscle cannot be stimulated as often as desired. To be precise, only about every 3-5 hours. This is called a muscle full effect.

This means that once protein synthesis in the muscle has been stimulated to the maximum, it is insensitive to further stimulation attempts for 3-5 hours.

The BCAAs play a central role in the energy balance in muscle tissue and in muscle building, and a special role is attributed to leucine.

The pure L-leucine capsules are made from natural, vegan, environmentally friendly amino acids obtained from fermentation. The capsule material is normally made from vegetable cellulose and is free from additives such as sugar, lactose, gluten, preservatives, flavourings or synthetic colourings.

Country of manufacture

BCAA products are food supplements and are therefore on the borderline between medicinal products and food. There are different guidelines for the production of these products and accordingly also different labelling obligations worldwide, which must be strictly observed.

When buying L-leucine products from the internet, you must carefully check the country of manufacture. In principle, products produced in EU countries have stricter guidelines than products from the USA, for example.

Suitable for vegetarians/vegans

Every L-Leucine in pure powder is made from 100% plant-based ingredients and is ideal for vegetarian and vegan diets. You can also combine the pure L-Leucine powder with vegan protein blends.

Pure L-leucine is obtained from the fermentation of corn and L-leucine amino acid, usually without genetic engineering and without additives. The pure products are also expensive, but strictly adhere to the prescribed conditions.

Facts worth knowing about L-leucine

You have already identified all the important buying criteria for the L-leucine product. In the next section you can find out more information and interesting facts about the amino acid L-leucine.

Which sources provide leucine?

Foods with a high L-leucine content are almost meat, dairy products and some nuts.

The following table gives you an overview of the foods with L-leucine in them:

Food Leucine content per 100g
Beef 2.9
Chicken breast 2.7
Tuna 2.4
Seeds 42.4
Pork 2.2
Nuts 1.5
Tofu 1.4
Eggs 1.1
Milk 0.3

Other foods in which L-leucine is naturally obtained are soybeans, peas, beef liver, cheese, peanuts, salmon, rice, and others.

What are the causes of leucine deficiency?

  • Malnutrition and undernourishment (eating disorders, low-protein diets)
  • Increased individual need due to heavy physical exertion, athletic training or chronic stress
  • Increased requirement due to liver disease
  • Increased need due to increased alcohol consumption
  • Reduced absorption due to vitamin B6 deficiency

What are the possible symptoms of leucine deficiency?

The following symptoms, some of which are unspecific, can indicate a leucine deficiency:

  • Fatigue
  • Fatigue
  • impaired wound healing
  • Growth and development disorders
  • Muscle cramps and stiffness
  • Weight gain

Image source: Oskanov/

References (7)

1. Leucin hat Wirkung auf die Muskelproteinbildung

2. Leucin hat Regulationsaufgabe des menschlichen Eiweißstoffwechsels

3. Überdosis von Leucine

4. Verbesserte Symptome nach einer täglichen regulierten L-Leucine Einnahme bei Lebererkrankung

5. Einnahme von Eiweißpräparaten zusammen mit Leucine

6. Leucin führt zu größerem Körperfettverlust während einer Diät

7. Leucin wirkt auf die Proteinbildung

Orally administered leucine stimulates protein synthesis in skeletal muscle of postabsorptive rats in association with increased eIF4F formation
Leucin hat Wirkung auf die Muskelproteinbildung
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Leucine as a regulator of whole body and skeletal muscle protein metabolism in humans.
Leucin hat Regulationsaufgabe des menschlichen Eiweißstoffwechsels
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Determination of the tolerable upper intake level of leucine in acute dietary studies in young men
Überdosis von Leucine
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Long-term oral branched-chain amino acid treatment in chronic hepatic encephalopathy. A randomized double-blind casein-controlled trial
Verbesserte Symptome nach einer täglichen regulierten L-Leucine Einnahme bei Lebererkrankung
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Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-aged Males
Einnahme von Eiweißpräparaten zusammen mit Leucine
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Leucine supplementation accelerates connective tissue repair of injured tibialis anterior muscle
Leucin führt zu größerem Körperfettverlust während einer Diät
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Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise
Leucin wirkt auf die Proteinbildung
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