The Amino Acid You Need to Build Muscle & 15 Foods That Have Plenty Of It

Amino acids are the building blocks of protein. There are 20 amino acids1, and they’re categorized into two groups: essential and non-essential.

Essential amino acids, including the branched-chain amino acids (BCAAs)—leucine, isoleucine, and valine—aren’t produced by the body in sufficient quantities and must be obtained through diet. Conversely, non-essential amino acids can be synthesized by the body.

Essential amino acids are involved in the production of proteins2, which are essential nutrients for optimal health and several bodily functions. Protein synthesis is the process by which the body builds and repairs tissues3, including muscles, organs, and cells. Additionally, protein plays a vital role in maintaining and building muscle mass4 in response to exercise. All 20 amino acids are required5 to support this process when protein synthesis is activated.

BCAAs have garnered special attention in the fitness industry due to their role in MPS5 and post-exercise recovery6. And leucine is one BCAA that's particularly important for enhancing muscle growth and repair. 

“Leucine is one of the main triggers of the mTROC1 signaling cascade, which is an important regulator of muscle protein synthesis (MPS),” explains David Church, Ph.D., an assistant professor at the University of Arkansas for Medical Sciences. “However, increases in mTORC1 signaling do not always equate to increased MPS or strength and mass gains. [That’s because] leucine on its own doesn’t increase in MPS.”

Summary

Amino acids are the building blocks of protein, and they're divided into essential and non-essential groups. Leucine is an essential amino acid that plays a role in muscle growth and repair.

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Leucine is a vital amino acid with remarkable importance for MPS and overall health. Don Layman, Ph.D., a leading amino acid researcher and professor at the University of Illinois at Urbana-Champaign, tells mindbodygreen, “After a protein-rich meal, the amount of leucine in the blood will increase and the increased level of leucine triggers a signaling system in the muscle known as mTOR. The mTOR system then stimulates the machinery involved in protein synthesis.”

So, how much leucine should you aim to consume daily to support muscle growth and repair? For optimal results, Layman suggests consuming around 2 to 3 grams of leucine per meal. For example, one large egg contains approximately 0.6 grams of leucine7, making it a convenient and affordable source.

While leucine is essential for muscle growth and repair, some research8 indicates that excessive leucine intake alone may not result in additional benefits. For this reason, Layman says it's smart to stagger your leucine intake throughout the day—starting at breakfast—instead of trying to cram all your leucine into one meal.

According to an older 2008 study, a diet lacking in leucine can have adverse effects on muscle growth and repair9 by potentially hindering the activation of mTOR and impeding MPS. Also, inadequate leucine intake can lead to muscle wasting and decreased muscle strength over time. That’s why eating leucine-rich foods is critical to ensure you're meeting the recommended daily intake and supporting your muscle health.

While leucine is important, other amino acids are too. For this reason, consuming a wide variety of high-protein foods is ultimately the best way to support your muscle-building goals and overall health.

Summary

Leucine triggers mTOR, a signaling system, which then stimulates muscle protein synthesis. A lack of leucine can potentially hinder muscle growth. Aim to consume 2 to 3 grams of leucine during every meal of the day.

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Plant proteins generally contain lower levels of leucine10 compared to animal proteins. “For example," says Layman, "grains such as wheat and quinoa contain less than 7% leucine, and legumes such as soy or pea contain about 8% leucine.” Chicken breast, on the other hand, is about 12% leucine.

However, with careful dietary planning, vegetarians and vegans can obtain sufficient leucine to support muscle growth and overall health.

Since plant proteins may not provide optimal amounts of leucine individually, plant-based eaters can ensure adequate leucine intake by combining different plant protein sources11. For example, eating legumes, grains, nuts, and seeds, can create complete protein profiles that offer all the essential amino acids, including leucine. 

In addition, prioritizing leucine-rich plant-based foods like tofu, tempeh, edamame, pumpkin seeds, and certain legumes can further boost your leucine intake.

“For vegetarians, it’s straightforward to get enough leucine by consuming dairy and eggs,” says Church. “Vegans need to consider complementary protein sources such as corn, soy, and rice. However, modern commercially available protein isolates and essential amino acid supplements (generally from vegan sources) tend to be high in leucine content.”

Summary

While plant proteins often contain small amounts of leucine, a combination of plant protein sources can fill in the nutritional gaps to create a complete amino acid profile. Eating whole foods is best, but protein supplements can also help guarantee you are getting all of the essential amino acids you need.

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1.

It may lessen age-related muscle loss.

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2.

It may promote muscle growth and recovery when combined with resistance training.

3.

It may enhance bone health.

Breakfast: Oatmeal cooked with almond milk and topped with sliced bananas and chia seeds.

Lunch: Lentil soup with a side of spinach salad and sliced avocado.

Dinner: Grilled tofu stir-fry with a variety of colorful vegetables and brown rice.

Snack: Greek yogurt with sliced peaches and a small handful of pumpkin seeds.

Breakfast: Scrambled eggs with spinach and feta cheese.

Lunch: Quinoa salad with chickpeas, diced cucumbers, cherry tomatoes, and a lemon vinaigrette.

Dinner: Grilled lean beef steak with roasted sweet potatoes and sautéed asparagus.

Snack: Cottage cheese with pineapple chunks and a handful of almonds.