If your biggest fitness goal is to build muscle, you probably already know how important protein is for helping you get there. What you might not know, however, is that your body needs specific amino acids for muscle growth. Yes, protein may get all the hype, but it’s the amino acids inside that do all the heavy lifting—and three of them stand out for their muscle-building power. 

Below, registered dietitians break down everything you need to know about this trio and which types of foods you should stock up on to get plenty of these amino acids for muscle growth.

What Are Amino Acids?

“Amino acids are the building blocks of protein, which is what our muscles and lots of other structural components of our bodies are made from, including cells, tissues, and organs,” explains Alissa Palladino, RDN, a registered dietitian and certified personal trainer. “Some can be made within our bodies, but nine of them are essential, which means we must obtain them from our diet.”

Our bodies need 20 amino acids overall to develop and function, but the nine essential amino acids we get from our food are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Foods that contain adequate levels of these amino acids and can be easily digested and absorbed are considered “complete proteins.” They typically come from animal sources, so you can get a good dose of them from a juicy steak or pan-seared salmon.

Many plant proteins are considered incomplete, with a handful of exceptions such as tofu and edamame. But if you’re vegetarian or vegan, don’t worry: “As long as you are eating a variety of plant-based protein sources, you will end up getting what you need,” Palladino says.

The Role of Amino Acids In Muscle Growth

Although each essential amino acid is responsible for different functions, all of them help repair muscle tissue, says sports dietitian Holley Samuel, RD, of Holley Fueled Nutrition. But it’s the three branched-chain amino acids (BCAAs) that play a starring role in muscle protein synthesis, the process in which your body turns the protein you eat into new muscle. 

BCAAs (which get their name from their chemical structure) “are not degraded in the liver like many other amino acids, but are metabolized in other tissues throughout the body, especially muscle tissue, which is one reason why they are associated with improving muscle growth and recovery,” Samuel explains.

As Palladino reminds us, the first step for muscle growth is strength training. In a nutshell, exercise creates microtears in our muscle fibers. To patch those fibers back together and make them stronger and more resilient, your body looks for new amino acids to replace the old ones. “The protein we eat then gets broken down into amino acids, which are used to repair and rebuild muscle,” Palladino says.

That’s why it’s so beneficial to sneak in some protein as soon as possible after you hit the weights—without that sufficient supply of amino acids, your body can’t keep up with repair demands, which can lead to slower recovery or even muscle breakdown. Replenishing with amino acids allows new muscle to be made.

3 Amino Acids for Muscle Growth

Leucine, isoleucine, and valine are the three branched-chain amino acids, and they’re your best friends when trying to build muscle. 

Leucine is the most powerful amino acid for muscle growth because it’s thought to stimulate the actual muscle protein synthesis process, but isoleucine and valine also play important supporting roles along the way. Without enough of all three, your gains could stall—even if you’re hitting your workouts hard. 

Here’s a bit more on why each of these three amino acids are so important for muscle growth.

1. Leucine

Leucine acts as a sort of “green light” to muscle growth. It triggers muscle protein synthesis “by signaling to pathways that other amino acids are available to start the muscle repair process post-exercise,” explains Samuel, adding that you need at least 2–3 grams of leucine to stimulate the process. 

Research also illustrates leucine’s role in promoting muscle growth and metabolic health. A small 2020 study published in the journal Nutrients, for example, found that leucine helped moderately reduce muscle damage in young men after a short bout of resistance exercise. This amino acid also helps heal wounds and balance blood sugar levels, according to the Cleveland Clinic.

2. Isoleucine

Isoleucine also contributes to muscle protein synthesis, playing a vital but not quite as influential role as leucine. It appears to increase muscle mass by promoting myogenesis, the process by which we actually form muscle tissue, according to a 2021 study in mice published in Food & Function.

BCAAs, especially isoleucine, also help increase the uptake of glucose into cells, according to Samuel. Because glucose is your body’s main fuel source, isoleucine may indirectly help boost your energy (although more research is needed). And the more energy you have, the harder you can hit your muscle-building workouts.

3. Valine

Valine acts as a complement to the other two BCAAs: It’s used to make glucose in the body and helps improve muscle protein synthesis when paired with leucine and adequate levels of other amino acids, Samuel says.

Plus, a 2023 study published in Bioscience, Biotechnology, & Biochemistry indicates that valine improves mitochondrial function, aka the body’s ability to generate energy from the food we eat.

What’s the Best Way to Get Amino Acids?

Samuel recommends getting your amino acids from the animal-based foods they’re often found in, like meat, dairy, poultry, seafood, and eggs. If you’re vegetarian, you can also turn to soy-based foods or a mix of plant-based proteins. All of the above are preferable over BCAA supplements, she says. 

“Research doesn’t support that [BCAA supplements] alone are enough to trigger muscle protein synthesis,” she says. “We need a complete protein source, which would come best from whole food or high-quality protein powder supplements that contain adequate leucine and are third-party tested.” (Remember, it’s best to get your healthcare provider’s approval before trying any new supplements.)

And, while the BCAAs are the keys to muscle protein synthesis, don’t forget about the other essential amino acids. While research indicates that BCAAs stimulate muscle growth, it also shows that eating a complete protein source with all nine essential amino acids provides the strongest stimulation response to muscle protein synthesis. According to Samuel, other research has shown that in order for leucine to stimulate muscle protein synthesis, there must be adequate levels of other amino acids present.

“You want to get enough amino acids throughout your daily diet so that there is an abundant enough pool of aminos for your body to use to repair itself throughout the day and week,” she says. If you’re active, you should be getting in 1.2–2 grams of protein per kilogram of bodyweight per day across a variety of foods. “We want to be considerate about refueling with adequate protein (specifically sources that contain adequate leucine) post-exercise to kick start the recovery process in addition to getting enough carbohydrates and hydration, which are also essential to proper recovery and overall health,” Samuel says.

While your protein needs probably look different than the person running on the treadmill next to you, Palladino says a good rule of thumb is to eat 20–30 grams of protein per meal and 10–15 grams for snacks. That way, your protein intake is spread evenly throughout the day for maximum muscle protein growth.

“Try to include a protein-rich food with every meal and snack—a veggie omelet or Greek yogurt parfait for breakfast, turkey or tuna sandwich for lunch, shrimp or tofu stir fry for dinner, or a handful of nuts or roasted chickpeas for snacks,” Palladino suggests.

The Takeaway

Amino acids are the building blocks of protein and are essential for growing and repairing all tissues in the body, including your muscles. Of the 20 amino acids, nine are essential, meaning that our body doesn’t make them so we need to get them from our food.

Of these nine essential acids, the three branched-chain amino acids (BCAAS)—leucine, isoleucine, and valine—are instrumental to muscle protein synthesis, in which your body breaks down protein into muscle. Leucine specifically helps kick off this process, but it’s not effective enough on its own.

While this trio is known for their muscle-building power, it’s important to get all essential amino acids into your diet so your body can repair itself. They’re best found in animal-based foods like meat or dairy, but if you’re vegetarian or vegan, you can also get them from soy-based foods like tofu or a mix of plant-based proteins.