How to Use Leucine for Bodybuilding and Gaining Muscle

If you're trying to max out your muscle gains or bulking up with bodybuilding, leucine (or L-leucine) is one of the most important nutrients you can eat.

That's because leucine plays an enormous role in telling your muscle fibers to use the protein and other amino acids you eat to grow, says Gabriel Wilson, PhD, CSCS, a certified strength and conditioning specialist at the Applied Science and Performance Institute in Tampa, Florida. Leucine works as an anabolic trigger and is metabolized directly in muscle tissue.

Here's everything you need to know about the importance of leucine for muscle growth and how to feed your muscles what they need.

What Is L-Leucine?

Leucine is one of 20 amino acids that serve as the building blocks of proteins, says Albert Matheny, RD, CSCS, registered dietitian and co-founder of Soho Strength Lab in New York City. Every protein in your body — and every protein you eat — is made up of some combination of these amino acids.

Of these 20 amino acids, L-leucine is one of three essential aminos known as branched-chain amino acids (BCAAs). They're called essential because your body can't produce them on its own. You have to get them from food or supplements, Dr. Wilson says.

These three BCAAs — leucine, isoleucine, and valine — are key to muscle protein synthesis (that is, muscle growth or hypertrophy). “They're rate limiting, so without enough of them, your recovery from working out is hindered,” Matheny says.

How Leucine Boosts Muscle Growth

All BCAAs help your muscles bounce back and grow bigger and stronger, but “leucine, in particular, is unique in its ability to stimulate muscle protein growth,” Wilson says. Basically, without leucine, muscle growth can't start.

The theory is that when levels of the amino acid in your blood increase, they flip the switch on a signaling chain called the mechanistic target of rapamycin pathway. That mechanistic target of rapamycin pathway is in charge of telling your body to shift into a state of growth, also called an anabolic state, Wilson explains.

Because it acts as the green light signaling your body to build muscle, leucine can ultimately help increase your overall muscle growth and lean body mass, according to the University of Rochester Medical Center in New York. It can also help athletes who are injured avoid declines in muscle mass, according to a review published in 2020 in Nutrients.

How Much Leucine Do You Need per Day?

The recommended daily intake for leucine is 17.7 milligrams (mg) per pound of your body weight, according to MyFoodData.com. So, a person weighing 180 pounds should get around 3,186 mg, or 3.186 grams (g), of leucine per day.

That said, if you're bodybuilding or actively trying to maximize your muscle growth, you will likely need much more. The International Society of Sports Nutrition position stand on protein and exercise states that athletes need 700 to 3,000 mg (up to 3 g) of leucine every 3 to 4 hours throughout the day. That is several times the current recommended daily intake.

That said, more leucine doesn't always equal more muscle. “There appears to be a ‘leucine threshold,’” says Wilson, which means that past a certain leucine dosage, you may not reap additional muscle growth.

For example, a 2020 study found that high-dose leucine supplementation didn’t appear to prevent any functional declines in young, healthy males who experienced limb immobilization.

Are You Getting Enough Leucine From Food?

Luckily, there are plenty of leucine-rich foods out there, Wilson says. Because foods high in protein generally contain leucine, you're probably getting enough of this essential amino acid — if you're getting enough quality protein, that is — says Matheny. Supplements, specifically whey protein and BCAA powders, are also a popular way to make sure you're meeting your needs.

According to a 2021 review, animal proteins are usually higher in L-leucine than plant proteins.

Should You Take Leucine Supplements?

If you're not eating animal-based proteins, you may need to eat more protein to cover your daily leucine dosage needs. However, it could potentially be more food than is feasible, comfortable, or healthy for you.

That's where supplementing with L-leucine, a BCAA, or protein powder comes in handy.

But plant eaters aren't the only ones who might want to supplement with leucine. If you're into fasting (or at least exercising while fasted, like first thing in the morning before having breakfast), you may need to increase your intake to get the full benefits of leucine.

“Since leucine and other amino acids play other roles in your body besides building muscle, if you're low on them because of fasting, your body breaks down muscle to use those amino acids for other priorities,” Matheny says.

If you’re not sure whether you’re meeting your leucine or overall protein needs, talk with your doctor. They can help you take a closer look at your diet and make any adjustments needed to reach your health, fitness, and muscle goals.

How and When to Take Leucine for Muscle Growth

Take 2.5 g of leucine or 5 g of total BCAAs 30 minutes or less after training to encourage an anabolic stimulus.

Immediately after a workout is the best time to take leucine. Taking a supplement 15 to 30 minutes post-workout will help your body start repairing your muscles, Matheny says. This is especially helpful if you work out several times per week on back-to-back days.

But in some cases, you might also want to incorporate a leucine-rich supplement during your workouts. By keeping your muscles fueled with leucine and other BCAAs, you can minimize the muscle breakdown that often occurs during long bouts of exercise, for example, while long-distance running or cycling.

Taking leucine while exercising can also be beneficial if you're working out after hours without eating, like if you're intermittent fasting and bodybuilding or just don't have time to eat before hitting the gym, Matheny says.

If you want a BCAA supplement, opt for one that contains a leucine dosage of at least 2.5 g per serving, Wilson suggests.

If you prefer to stick with a protein powder, whey will be the richest source of the amino acid. You can get enough from plant-based protein powders, too. Just check the label to see how much leucine a serving offers.

Also make sure the supplement you choose is tested by an independent, third-party lab like US Pharmacopeia or the National Science Foundation and the ingredient list is as short as possible.