Leucine: The Muscle-Building Amino Acid Your Body Needs

January 9, 2024

A favorite of both bodybuilders and pro athletes alike, leucine is revered for its incredible ability to boost muscle mass and improve athletic performance. Not only that, but it can also slow muscle deterioration in older adults and help keep blood sugar under control.

Luckily, there are plenty of options for upping your intake of this essential amino acid to take advantage of its powerful effects, from both supplements and food sources. In fact, it’s found in many of the foods that you probably already eat on a daily basis.

So what is leucine, and should you consider adding it into your regimen? Keep reading for what you need to know about this branched-chain amino acid and how it can affect your health.

What Is Leucine?

Leucine is an essential amino acid that is integral to the synthesis of muscle. The leucine structure contains an alpha-amino group, an alpha-carboxylic acid group and a side chain isobutyl group, making it a branched-chain amino acid.

Branched-chain amino acids cannot be produced by the body and need to be obtained from food sources. These amino acids are broken down in the muscles instead of the liver, helping enhance energy production and muscle synthesis during exercise.

However, leucine is often considered preferable to other branched-chain amino acids (BCAAs) because it’s broken down and absorbed more rapidly, allowing it to be used more readily than other types, such as isoleucine and valine.

The leucine amino acid can also be broken down directly into acetyl-CoA, making it one of the most important ketogenic amino acids in the body. While most other amino acids are converted into glucose, the acetyl-CoA formed from leucine can be used to make ketone bodies.

It is found naturally in many food sources and also commonly taken in supplement form for its muscle-boosting benefits. Other purported benefits include enhanced fat loss, improved muscle recovery, better physical performance, decreased muscle loss and better blood sugar control.

Leucine was first discovered and isolated from cheese by a French chemist named Joseph Louis Proust in 1818. Just a year later, it was officially named and isolated from muscle fibers in its pure form by chemist and pharmacist Henri Braconnot.

The three branched-chain amino acids, including leucine along with isoleucine and valine, are among the nine essential amino acids that your body needs and account for about 35 percent of all essential amino acids found in muscle proteins.

In recent years, the importance of essential amino acids has come to light as more research continues to emerge. In 2002, the U.S. Institute of Medicine set the first official guidelines, recommending that adults should get at least 42 mg/kg body weight of leucine each day.

Today, branched-chain amino acids are widely used in the treatment of a range of conditions. Preliminary research suggests that certain branched-chain amino acids may have therapeutic effects for trauma and burn victims, as well as conditions like hepatic encephalopathy.

Benefits

1. Builds Muscle

L-leucine is a popular supplement among bodybuilders and athletes due to its powerful effects on muscle gaining. As one of the key amino acids involved in muscle synthesis, it may help trigger muscle building to optimize your workout.

However, research has turned up mixed results on the potential effects of this amino acid. One long-term study out of France, for example, found that leucine was much more effective in promoting muscle growth and enhancing performance when it was combined with other amino acids rather than consumed alone.

Including a good variety of protein foods in your diet can help maximize the effects of leucine by providing a wide array of amino acids and essential nutrients to fuel muscle growth.

2. Prevents Muscle Loss

As you get older, there are a lot of changes that happen in your body. Sarcopenia, the gradual deterioration of skeletal muscles, is one of the most notable effects of advanced age. This condition can cause weakness and decreased stamina, leading to a decline in physical activity.

Leucine is believed to help slow muscle deterioration to decrease the effects of aging. One study conducted at the University of Texas Medical Branch’s Department of Internal Medicine and published in Clinical Nutrition showed that it helped improve muscle synthesis in older adults consuming the recommended amount of protein per meal.

Another human model, conducted in France and referenced above, had similar findings, reporting that leucine supplementation was also able to limit weight loss caused by malnutrition in elderly participants.

3. Improves Performance

In addition to using leucine for bodybuilding, both professional and novice athletes alike often turn to this essential amino acid looking to bump up their physical performance to the next level.

One study conducted at the Institute of Sport and Exercise Science at James Cook University in Australia and published in the European Journal of Applied Physiology reported that taking leucine supplementation for six weeks significantly improved both endurance and upper-body power in competitive canoeists. Similarly, another study published in the European Journal of Clinical Nutrition in 2016 showed that leucine supplementation enhanced lean tissue mass and improved functional performance in older adults.

4. Aids in Fat Loss

If you’re looking to build muscle and simultaneously shed some extra body fat, leucine may be just what you need. In fact, several studies have found that it can have some powerful effects when it comes to fat loss.

An animal model out of the University of São Paulo’s Department of Food Science and Experimental Nutrition in Brazil showed that supplementing rats with a low dose of leucine for a six-week period resulted in increased fat loss compared to a control group. According to a 2015 review in Nutrients, this amino acid has also been shown to decrease fat accumulation during aging and prevent the development of diet-related obesity.

5. Promotes Muscle Recovery

Cramps and sore muscles are pesky problems that many people face after hitting the gym. Following an especially intense workout, these muscle aches can sometimes even be enough to keep you from the gym a few days, completely throwing off your schedule and delaying your fitness goals.

Studies have found some promising results on the potential role of leucine in muscle recovery. A review from the Department of Food Science and Human Nutrition at the University of Illinois reported that consuming leucine right after working out can help stimulate muscle recovery and muscle protein synthesis.

Another study conducted at the School of Sport and Exercise and the Institute of Food, Nutrition and Human Health at Massey University in New Zealand demonstrated that supplementation with this amino acid improved recovery and enhanced high-intensity endurance performance in male cyclists after training on consecutive days.

6. Stabilizes Blood Sugar

Hyperglycemia, or high blood sugar, can wreak havoc on your health. In the short term, high blood sugar can cause symptoms like fatigue, unintentional weight loss and increased thirst. Left unchecked for even longer, high blood sugar can have even more serious consequences, including nerve damage, kidney problems and a higher risk of skin infections.

Some research suggests that leucine may be able to help maintain normal blood sugar levels. A human study out of the VA Medical Center’s Endocrine, Metabolism and Nutrition Section in Minneapolis and published in Metabolism showed that leucine taken alongside glucose helped stimulate insulin secretion and decrease blood sugar levels in participants.

A 2014 in vitro study out of China also showed that leucine was able to facilitate insulin signaling and glucose uptake to help keep blood sugar levels in check.

Risks, Side Effects and Interactions

Consuming the leucine found in foods is safe with minimal risk of side effects. Taking a leucine supplement, on the other hand, can increase the risk of leucine side effects, like chronic fatigue and impaired coordination.

It may interfere with the production of niacin from L-tryptophan and can aggravate symptoms of pellagra in those with a niacin deficiency. It also can reduce the release of serotonin, an important neurotransmitter involved in the regulation of mood and anxiety, as research out of the University of Pittsburgh School of Medicine’s Department of Psychiatry at the Western Psychiatric Institute and Clinic and published in the Journal of Nutrition shows.

High doses of leucine can also be toxic and cause increased levels of ammonia in the blood. Although there is no official upper tolerable intake level set for leucine, some studies suggest that intake should be limited to less than 500 mg/kg of body weight to minimize the risk of side effects.

For those with a condition called maple syrup urine disease (MSUD), intake of leucine and other branched-chain amino acids must be carefully monitored. This genetic condition, typically presenting in infants, is caused by the lack of an important enzyme used to break down branched-chain amino acids.

This can lead to a buildup of compounds like leucine and keto acids in the blood, causing symptoms, such as lethargy, weight loss, irritability and even neurological damage. Individuals with this condition should be followed closely by a doctor and dietitian to determine the best course of treatment.

Research is limited on the effects of leucine in women who are pregnant and breastfeeding, so it’s best to talk with your doctor before starting supplementation. Additionally, if you experience any persistent adverse side effects while taking leucine supplements, be sure to consult with a qualified health care professional.

Foods

In addition to taking a leucine supplement, there are plenty of foods high in leucine that can help you get in your daily dose as well. It’s found in a variety of protein sources, such as meat, cheese and plant-based protein foods.

Here are a few of the top food sources of leucine that you may want to consider adding to your diet to increase your intake of leucine:

Eggs
Spirulina
Elk meat
Chicken
Oats
Tuna fish
Grass-fed beef
Lentils
Turkey breast
Cottage cheese
Sesame seeds
Venison
Peanuts
Wheat germ
Hemp seeds

Recipes

Looking for some simple and delicious ways to bump up your leucine intake? Head over to the kitchen, and give these easy leucine-rich recipes a try:

Dosage and Uses

L-leucine is often used by athletes looking to increase muscle mass, enhance recovery, and improve endurance and strength. It’s also used to slow the natural breakdown of muscles that comes with advanced age.

Available in both capsule and powder form, it’s generally used in doses between 2,000–5,000 milligrams per day for maximum effectiveness and is typically taken alone or alongside low-protein meals. As always, it’s best to start at a lower dosage and work your way up slowly in order to assess your tolerance.

One of the most common complaints with leucine supplements is that leucine powder has an especially bitter, unpleasant taste. Masking the taste with natural sweeteners is one strategy often used to hide the intense flavor. You can also try blending it with drink mixes or adding it to a healthy smoothie to increase the palatability as well.

Capsules are also available as an easy alternative to get in your daily serving, flavor-free.

Leucine vs. Lysine

There are plenty of similarities between leucine and lysine in terms of structure, function and the way that your body uses these important amino acids.

Like leucine, lysine is also considered an essential amino acid, meaning that you must obtain it through the diet as your body is unable to synthesize it on its own. It’s also considered a ketogenic amino acid, as it’s broken down directly into acetyl-CoA, the molecule used to produce ketone bodies.

While L-leucine is primarily used for its muscle-building properties, lysine has been associated with a wider spectrum of potential L-lysine benefits. It’s frequently used to help prevent herpes outbreaks, reduce anxiety, support gut health, and decrease the risk of diabetes symptoms and complications.

Lysine is found in many of the same food sources as leucine. Foods like grass-fed beef, turkey, chicken, tuna, pumpkin seeds, eggs and white beans, in particular, contain a concentrated amount of lysine, but it’s also available in supplement form and can be found in powders, capsules and creams.

Final Thoughts

Leucine is one of three branched-chain amino acids. It’s also considered an essential amino acid, meaning that your body is unable to synthesize it, so it must be obtained through food sources.
It’s been shown to promote and preserve muscle mass, improve athletic performance, increase fat loss, stabilize blood sugar levels, and support muscle recovery.
It can be taken in supplement form or consumed through protein foods like meat, seafood, poultry, eggs, dairy, nuts and seeds.
While this amino acid found in foods can be safely consumed by most, high doses from supplements can cause side effects and toxicity.
For best results, enjoy a variety of leucine-rich foods in combination with a nutritious and well-rounded diet to take advantage of the multitude of benefits this essential amino acid can provide.