How Leucine Supports Muscle Health and Other Benefits

Leucine is an essential branched-chain amino acid (BCAA) that some research suggests may help improve muscle mass, athletic recovery, inflammation, and blood sugar levels. However, further studies are needed to confirm many of these benefits.

Leucine is important for protein synthesis and muscle growth. It is sold as a dietary supplement and is found naturally in foods like chicken, turkey, and cheese.

In the United States, the Food and Drug Administration (FDA) does not regulate supplements the way it regulates prescription drugs. That means some supplement products may not contain what the label says. When choosing a supplement, look for third-party tested products and consult a healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist.

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Although further research is needed, people generally use leucine supplements to build muscle mass and improve exercise performance.

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Studies have looked at leucine's role in supporting muscle growth and recovery with mixed results.

Muscle Growth

Leucine is popular among bodybuilders due to its potential to support muscle growth. Branched-chain amino acids, especially leucine, have been shown to activate the mTOR signaling pathway, which promotes muscle growth.

However, the evidence is mixed. Leucine seems to offer the most health benefits to older adults—especially those with age-related muscle loss (sarcopenia)—when combined with strength training.

For example, one 2022 randomized control trial looked at the effects of leucine supplementation on body composition and physical function in healthy Korean adults 50 years and older. All participants completed a 12-week strength-training routine, with or without leucine supplements.

At the end of the study, the group that combined the leucine supplement with strength training experienced significant improvements in lean muscle mass compared to those who only did strength training.

However, a recent review of 17 randomized control trials found no improvements in lean muscle mass and strength in older adults who took an isolated leucine supplement without strength training.

Similarly, another small randomized control trial found no improvements in muscle mass or strength with high-dose leucine supplementation in resistance-trained men who consumed adequate dietary protein.

Most studies to date have been short-term and have reported improvements in muscle protein synthesis but not necessarily in muscle mass. Long-term human studies are needed to confirm the relationship between leucine and muscle growth.

Muscle Recovery

According to studies, leucine supplementation may help improve muscle recovery when combined with resistance training. It appears to be most beneficial when combined with other essential amino acids.

One recent study found that leucine-enriched essential amino acids can help reduce muscle damage in the days following an acute bout of resistance exercise. However, no significant improvements in muscle protein synthesis were observed during the study.

Another study examining leucine supplementation's effects on muscle recovery from resistance exercise in young adults found no significant improvements.

While inflammation is a normal part of your body's healing process, chronic inflammation can play a role in the development of many diseases, including heart disease, autoimmune disease, cancer, and diabetes.

One study in adolescents and young adults with cerebral palsy found that participants who were given leucine supplements for 10 weeks experienced significant improvements in markers of inflammation. Improvements in muscle strength, muscle soreness, mood, muscle mass, and overall well-being were also observed.

However, the study was small, including only 21 participants.

Human and animal studies show that supplementing with leucine, especially alongside glucose (sugar), may help stimulate insulin secretion, which may help control blood sugar.

In addition, a 2014 test-tube study noted that leucine could help improve insulin sensitivity and promote glucose uptake to help keep blood sugar levels under control.

However, further human studies are needed to confirm these effects.

Side effects are unlikely from consuming leucine-rich foods. However, consuming a leucine supplement may have potential side effects.

No severe side effects have been reported with leucine supplements when taken at recommended doses. However, taking high doses of leucine supplements may lead to some side effects, including:

High doses of leucine may interfere with the production of niacin from tryptophan, which can worsen symptoms of pellagra, a disease caused by a deficiency in niacin or tryptophan.

Studies have shown that doses over 500 milligrams (mg) per kilogram (kg) of body weight daily can increase ammonia in the blood. This can lead to elevated ammonia concentrations in the brain, which can cause neurological damage and confusion.

However, one study noted that blood ammonia levels returned to normal the day after the supplement was discontinued, causing no serious health consequences.

If you experience confusion, severe gastrointestinal discomfort, or other severe symptoms, stop taking leucine and contact your healthcare provider.

Active ingredient(s): Leucine

Alternate name(s): L-leucine, (S)-2-Amino-4-methylpentanoic acid, (S)-Leucine

Suggested dose: Varies depending on the health condition.

Safety considerations: It may not be safe for people who are pregnant, breastfeeding, or have certain health conditions, such as maple syrup urine disease.

People with existing health conditions, such as the following, should be aware of possible safety concerns when taking leucine supplements:

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

There are no official dosage guidelines for leucine supplements. However, a common dose is 5 grams (g) per day.

According to the World Health Organization (WHO), the average healthy adult should consume 39 mg/kg of leucine daily.

This means a 176-pound (80 kg) individual would need around 3.1 g of dietary leucine daily.

However, studies suggest that older adults may need more than double the current recommendations. For example, a leucine intake of 3 g during three main meals, along with 25 to 30 g of protein, is commonly recommended for older adults to prevent or recover from muscle loss.

Dietary supplements are not regulated like prescription medications in the United States. Therefore, some may be safer than others. When choosing a supplement, consider factors such as third-party testing, potential drug interactions, and other safety concerns. Talk to a healthcare provider or a registered dietitian nutritionist (RD or RDN) about supplement quality and safety.

There is little information about leucine overdoses and toxicity in humans. However, to prevent toxicity and severe side effects, be aware of the appropriate dosage and keep the upper limit in mind.

According to recent research, adults should limit daily leucine intake to less than 500 mg/kg or around 35 g for a person weighing 154 pounds (70 kg).

As mentioned previously, doses over 500 mg/kg can lead to elevated ammonia concentrations in the brain.

If you experience severe gastrointestinal discomfort or confusion, you may have taken too much and should seek immediate medical attention.

Use caution when taking leucine with the following medications:

It is essential to carefully read a supplement's ingredients list and nutrition facts panel to learn which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications.

Storage instructions may vary by supplement brand. Carefully read the product label to ensure you store your supplement properly.

Generally, dietary supplements should be stored in a cool, dry area in their original packaging. They should be kept out of the reach of children or pets, preferably in a locked cabinet.

Supplements should be discarded after one year or as indicated on the product label. Ask your healthcare provider or pharmacist any questions you have about how to dispose of your supplements or medications.

Leucine may be used to reduce inflammation, regulate blood sugar, and support muscle health.

Other supplements with similar properties include:

Leucine is a branched-chain amino acid that stimulates muscle protein synthesis. It may also support muscle health, exercise recovery, and healthy blood sugar levels.

Unless otherwise recommended by a healthcare provider, leucine can be taken daily. However, consuming it alongside other amino acids is important to sustain muscle protein synthesis and optimal health.

Leucine may be beneficial in improving muscle size and function in older adults, especially those who are frail and malnourished.

People who don't eat animal products may also benefit from a leucine supplement since the amino acid is commonly found in animal foods. However, there's not much evidence that it can benefit healthy young adults who are already consuming adequate amounts of leucine in their diet.

Leucine can be found in both food and supplement forms. However, consuming a well-balanced diet that includes high-leucine foods is best.

Unfortunately, most food guidelines do not list the amount of leucine in foods. This makes it difficult to build a dietary plan based on current guidelines.

Here is a look at the amount of leucine in 100 g of the following foods:

Leucine supplements are commonly sold in capsules or powder. Vegetarian and vegan options are also available. You can purchase leucine supplements online or in certain grocery, retail, or health food stores.

Follow a healthcare provider's recommendations or label directions to ensure proper dosage and avoid unwanted side effects from leucine supplements.

Leucine is a branched-chain amino acid that is important for rebuilding and repairing muscle tissue. There is some evidence that it may help improve muscle mass, recovery, inflammation, and blood sugar levels. It seems to be most beneficial for improving muscle function and counteracting the loss of muscle mass in older adults.

Before incorporating leucine supplements into your diet, talk with a healthcare provider to ensure it is appropriate for your health needs.

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U.S. Department of Agriculture. Beans, navy, mature seeds, canned.

U.S. Department of Agriculture. Lentils, mature seeds, cooked, boiled, without salt.

By Lindsey DeSoto, RD, LDLindsey DeSoto, RD, is a registered dietitian specializing in nutrition and health and wellness content.