The 9 Essential Amino Acids and Their Role in Building Muscle

Protein is necessary to build muscle. Bodybuilders and protein shakes are synonymous.

But there’s more to this than just protein powders and shakes. What type of protein should you eat? Which are the best protein sources for muscle building? Can vegetarians or vegans get the right protein to build muscle?

The answer lies in understanding the 9 essential amino acids and their food sources. Read on!

What are Amino Acids?

The building blocks of protein are called amino acids.

Various combinations of amino acids create different types of proteins. Amino acids are made up of even smaller units known as peptides.

Even though 20 varieties of amino acids are required by our body, only 9 of them are considered essential amino acids since these cannot be synthesized in our body (1).

Unlike carbs or fats, protein cannot be stored in the body. So bodybuilders must give extra emphasis to protein in their diets as this is the main nutrient that promotes the growth and repair of damaged muscle cells and other tissue.

What is a Complete Protein?

Dairy, eggs, meat, fish, pulses, and nuts are all healthy sources of protein. A food that contains all 9 essential amino acids is called a complete protein. Most animal protein sources provide complete proteins while plant protein sources are often lacking in many of the essential amino acids. Different amino acids have different roles in the body.

Vegan or vegetarian bodybuilders often end up missing out on certain essential amino acids in the diet. For instance, pea protein does not have any methionine, but it is rich in lysine (2). Vegans especially need to incorporate a variety of protein-rich foods in their diet to ensure they get adequate amounts of all 9 essential amino acids (3).

The 9 Essential Amino Acids and Their Sources

The nine essential amino acids are:

  • Lysine
  • Leucine
  • Isoleucine
  • Methionine
  • Histidine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

Now let’s take a deeper look at their functions and vegetarian food sources as non-vegetarian foods contain all 9 of them. To get a complete meal from vegetarian sources you can choose complementary foods.

1. Lysine

Lysine can be called one of the most essential amino acids as it is indispensable as far as the growth and development of the body is concerned. It is important for building new muscle protein and for maintaining it. Lysine also plays a role in maintaining nitrogen balance (4). It helps maintain lean body mass during periods of extreme stress and fatigue.

Bone and muscle growth are dependent on lysine as this amino acid is necessary for calcium absorption. Lysine plays an important role in fat mobilization for energy uses. It is necessary for the production of antibodies, enzymes, as well as hormones such as testosterone, insulin, etc. Lysine is required for the synthesis of collagen which, in turn, is necessary for the formation of connective tissue in our body.

Vegetarian sources of Lysine: peas, chia seeds, spirulina, parsley, avocados, almonds, cashews

2. Leucine

Leucine is extremely important for bodybuilders as this amino acid directly stimulates muscle strength and growth. Leucine is one of the three branched-chain amino acids (BCAAs) that are gaining popularity among bodybuilders.

Leucine activates mTOR(mammalian target of rapamycin), an essential compound that is necessary for up-regulating protein synthesis in the muscles (5). Leucine also plays a role in retaining lean muscle when dieting. Another important role of leucine is that it regulates blood glucose levels in the body during and after workouts, by moderating the insulin levels. This, in turn, has a positive effect on our brains and neurotransmitters.

Vegetarian sources of Leucine: soybeans, pumpkin, sunflower seeds, pistachio nuts

3. Isoleucine

Isoleucine is an isolated form of the amino acid leucine. It is a branched-chain amino acid (BCAA). Isoleucine aids in the production of hemoglobin (6). Hemoglobin not only transports iron in the blood, but it also plays a role in the regulation of blood sugar that is being burned as fuel for the muscles during exercise.

Isoleucine is also necessary for nitrogen growth in the muscle cells. Maintaining a positive nitrogen balance is extremely important for muscle building. The greater the nitrogen balance, the faster the recovery from workouts.

Vegetarian sources of Isoleucine: soya beans, cashews, almonds, oats, lentils, brown rice, legumes, chia seeds

4. Methionine

Methionine contains sulfur, which is integral to tissue and muscle health (7). A deficiency of sulfur in the body increases the risks of arthritis and damaged tissue. This also causes trouble with healing from injuries. Methionine assists in muscle growth. It also helps in dissolving fat deposits within various areas of the body, including the liver.

This amino acid is necessary for the formation of the non-essential amino acid, creatine (8). Creatine is stored in the skeletal muscles and it is needed for the creation of energy-releasing ATP molecules. Creatine helps in recharging energy levels during high-intensity exercise and training.

Vegetarian sources of Methionine: chia seeds, brazil nuts, oats, wheat, figs, whole grain rice, legumes, onions, cocoa

5. Histidine

Histidine is needed for the growth and repair of tissues of all kinds, including muscle tissue. This amino acid supports brain health and neurotransmitters. Histidine is a precursor to synthesizing histamine, a non-essential amino acid that gets released by the immune system in response to allergies (9).

Histidine is needed for the overall health and immunity of our body as it helps in the production of red and white blood cells. Histidine also aids the production of gastric juices thus improving digestion.

Vegetarian sources of Histidine: soybeans, legumes, buckwheat, potatoes, chia seeds,

6. Phenylalanine

The essential amino acid Phenylalanine is converted into the amino acid tyrosine inside our body (10). Tyrosine is a precursor for neurotransmitters such as dopamine, and adrenaline. The concentrations of these brain chemicals in the body and brain are dependent directly upon the dietary intake of phenylalanine. These chemicals have a strong impact on our mood and mental health.

Tyrosine is also required for the production of various proteins and thyroid hormones (11). Tyrosine is an important amino acid that is required for the production of enkephalins, the body’s natural pain reliever.

Vegetarian sources of Phenylalanine: spirulina, seaweed, pumpkin, beans, rice, avocado, almonds, peanuts, quinoa, figs, raisins, leafy greens, olives

7. Threonine

Threonine is essential for keeping the muscles strong and elastic. Threonine is an essential amino acid that is required for the production of glycine and serine, the two non-essential amino acids which, in turn, are needed to create elastin, collagen, and muscle tissue (12).

Threonine has a role in building strong bones. It accelerates the healing of both superficial wounds as well as tissue injuries. Threonine aids the immune system, the liver, the heart, and even the central nervous system.

Vegetarian sources of threonine: Wheat germ, nuts, soya beans, kidney beans, flax seeds, sesame seeds

8. Tryptophan

You must be aware that serotonin is a neurotransmitter that makes us feel happy. It lowers stress levels and depression. What you may not know is that the amino acid tryptophan is converted into serotonin in the brain (13).

Tryptophan promotes healthy sleep patterns as it induces a relaxing effect on the body. It supports brain function and nervous system function.

Vegetarian sources of tryptophan: chocolate, chickpeas, almonds, sunflower seeds, spirulina, bananas, peanuts

9. Valine

Valine is essential for endurance and overall muscle health. Along with Leucine and Isoleucine, Valine is one of the three famous branched-chain amino acids (BCAAs). During physical activity, this amino acid helps prevent the breakdown of muscle tissue. It also supplies extra glucose to the muscles for energy production. Valine has been proven to help alleviate disorders of the muscles (14).

Valine has many roles which include supporting the nervous system and aiding cognitive functions. It is also needed for healing and curing metabolic and liver diseases. Valine improves insomnia and nervousness. It is also an effective appetite suppressant.

Vegetarian sources of valine: nuts, beans, spinach, legumes, broccoli, chia seeds, figs, avocado, apples, blueberries, and apricots.

An Extra Word on BCAAs – Myth or Truth?

Since there is so much hype surrounding branched-chain amino acids (BCAAs), let’s take a closer look at these particular amino acids- namely leucine, valine, and isoleucine. The BCAAs are considered different from other essential amino acids as they are metabolized mostly in the skeletal muscles rather than the liver (15).

BCAAs are claimed to improve protein absorption, reduce muscle fatigue, replenish energy levels, increase recovery rates and help build muscle faster. You may have even heard that not taking enough BCAAs can cause muscle loss in bodybuilders. Well! There is some truth in there, but not all of it.

When Robert R. Wolfe University of Arkansas for Medical Sciences, published a study “Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?” in the Journal of the International Society of Sports Nutrition (16). It caused an uproar in the protein supplements industry and BCAA supplements took on a major bashing.

But Wolfe’s research never said BCAAs don’t work. Wolfe noted that supplementation with BCAAs alone increases muscle breakdown “because the other EAAs (essential amino acids) required for the synthesis of a new protein can only be derived from muscle protein breakdown.”

This means no matter how much BCAAs you take, your body requires other essential amino acids too. so it will break down your muscles to get those amino acids. If your diet is inadequate in essential amino acids, then focusing on just BCAA supplementation alone will lead to muscle breakdown and not muscle building!

Before You Go…

Bodybuilders do need BCAAs, but this does not mean chugging down BCAA supplements is all the protein nutrition that’s needed.

If anything else, Wolfe’s research serves as a reminder that all essential acids are important for bodybuilding, and excluding any of them will negatively affect your muscle-building efforts.

About Anju Mobin 104 Articles
The Nutritionist Wordsmith with a Chocoholic Edge! Anju is not just a writer; she's a brush-wielding, coffee-sipping, chocolate-loving wordsmith! With a Fine Arts degree in one hand and a Home Science degree in the other, she blends creativity and nutrition to craft content that truly nourishes the mind. Whether she's painting a vivid picture with words or brewing up engaging web content, she pours her heart into every project. When she's not busy whipping up articles, you'll find her nurturing orchids to bloom in her garden, baking scrumptious treats, and indulging her chocoholic tendencies with dark delights. She is the founder and managing editor of Fitness Hacks.