Essential vs Nonessential Amino Acids: Let’s Break It Down

Amino acids are organic compounds that combine to form proteins. They are the building blocks of proteins and play a central role as intermediates in metabolism. In nutrition, amino acids are classified as either “essential” or “nonessential” — but what exactly does that mean?

What is the difference between essential and nonessential amino acids? How many amino acids are there?

According to a 2020 article titled “Biochemistry, Essential Amino Acids,” essential amino acids are a group of amino acids that the human body cannot synthesize from metabolic intermediates. Simply put, essential amino acids are amino acids that cannot be made by the body. These amino acids must come from a person’s diet, as the human body lacks the metabolic pathways required to synthesize these amino acids. Essential amino acids are also known as “indispensable amino acids.”

Conversely, nonessential amino acids (also known as “dispensable amino acids”) are amino acids that the human body is capable of synthesizing using only the essential amino acids. In other words, the body is able to produce them. Nonessential amino acids do not need to come from the diet. 

Although there are hundreds of amino acids found in nature, only about 20 amino acids are needed to make all the proteins found in the human body. Per the article, it bears mentioning that there is another amino acid considered to be the 21st acid: selenocysteine. Selenocysteine was a more recently discovered amino acid that may become incorporated into protein chains during protein synthesis.

Pyrrolysine is considered the 22nd amino acid; however, pyrrolysine is not used in human protein synthesis.

Why are essential amino acids called essential? What is the difference between essential and conditionally essential amino acids?

The article referenced above notes that these “essential” and “nonessential” classifications are a result of early studies on human nutrition that found that specific amino acids were required for growth or nitrogen balance, even when there was an adequate amount of alternative amino acids. 

The classifications were first reported in nutritional studies done in the early 1900s. One study from 1957 found that the human body was able to stay in nitrogen balance with a diet of only eight amino acids. These eight were the first amino acids to be deemed essential amino acids. At this time, scientists could identify essential amino acids by conducting feeding studies with purified amino acids. Researchers found that when they removed individual essential amino acids from a diet, the study’s subjects were unable to grow or stay in nitrogen balance. 

Eventually, there was the creation of an additional classification: conditionally essential amino acids. Conditionally essential amino acids are amino acids that become essential in certain situations. Researchers found that certain amino acids are conditionally essential depending on a person’s metabolic state. For example, the article states that amino acids like arginine and histidine may be considered conditionally essential because the body cannot synthesize them in sufficient quantities during certain physiological periods of growth, such as pregnancy, adolescent growth, recovery from trauma, etc. The article gives the example of a healthy adult who may be able to synthesize tyrosine from phenylalanine compared to a young child who has not developed the required enzyme to perform this synthesis. The child would be unable to synthesize tyrosine from phenylalanine, making tyrosine an essential amino acid in this situation. 

Due to the existence of conditionally essential amino acids, the terms "essential amino acid" and "nonessential amino acids" can be somewhat misleading since all amino acids may be necessary to ensure optimal health. Additionally, “nonessential” is a slightly misleading label because these amino acids do fill essential roles — it’s just that they are synthesized by your body, so they’re not an essential part of your diet. 

To avoid unnecessary confusion, we’ll stick to the two original classifications and divide amino acids into the two basic categories of essential amino acids (which, again, are the amino acids the human body must get through foods) and nonessential amino acids (which are the amino acids that the average human body can synthesize and are not an essential part of your diet).

What are the essential and nonessential amino acids?

The 21 amino acids that comprise proteins include: 

• Alanine

• Arginine

• Asparagine

• Aspartic Acid

• Cysteine 

• Glutamic acid

• Glutamine 

• Glycine

• Histidine

• Isoleucine

• Leucine

• Lysine

• Methionine

• Phenylalanine

• Proline

• Serine 

• Threonine

• Tryptophan 

• Tyrosine 

• Valine

• Selenocysteine

Of these amino acids, these nine are essential: 

• Phenylalanine

• Valine

• Tryptophan

• Threonine

• Isoleucine

• Methionine

• Histidine

• Leucine

• Lysine

The others are nonessential: 

• Alanine

• Arginine

• Asparagine

• Aspartic Acid (or aspartate)

• Cysteine 

• Glutamic acid (or glutamate)

• Glutamine 

• Glycine

• Proline

• Serine 

• Tyrosine 

• Selenocysteine

What do the essential amino acids do? What foods are they found in?

The essential amino acids perform a number of important roles in the body. According to compound summaries published by the National Library of Medicine, phenylalanine plays a key part in the biosynthesis of other amino acids. It is a precursor for neurotransmitters like tyrosine and dopamine, and it’s important in the structure and function of many proteins and enzymes. Phenylalanine is found in popular protein-containing foods:  beef, chicken, pork, tofu, fish, beans, milk, eggs, cheese, nuts and soybeans.

One of the three branched-chain amino acids (BCAAs), valine helps stimulate muscle growth, tissue repair and energy. Valine is commonly found in soy, cheese, peanuts, mushrooms, healthy carbohydrates like whole grains and vegetables.

Tryptophan is needed to maintain proper nitrogen balance. It’s a precursor to serotonin, a neurotransmitter that regulates your mood, appetite and sleep. Tryptophan can be found in foods like chocolate, poultry, milk, yogurt, cheese, red meat, eggs, fish, oats, dried dates, sesame, chickpeas, almonds, sunflower seeds, pumpkin seeds and peanuts. 

Threonine is a residue of many proteins, such as tooth enamel, collagen and elastin. Threonine is also a crucial amino acid for the nervous system, playing an important role in fat metabolism and preventing fat buildup in the liver. This essential amino acid has also been used to alleviate anxiety and mild depression. Like phenylalanine, popular protein foods like lean beef, chicken, pork, tuna, tofu, beans, milk, cheese, eggs, seeds and nuts are often high in threonine. 

Also one of the BCAAs, isoleucine has diverse physiological functions. Isoleucine assists wound healing, helps detoxify nitrogenous wastes, stimulates the immune system and promotes secretion of several hormones. Necessary for regulating blood sugar and energy levels, isoleucine is concentrated in human muscle tissues. Isoleucine is plentiful in foods like meats, fish, cheese, eggs and most seeds and nuts.

Methionine is required for growth and tissue repair. It plays an important role in metabolism and detoxification, and it’s necessary for tissue growth and the absorption of the minerals zinc and selenium. Methionine also acts as a lipotropic agent and prevents excess fat buildup in the liver. Foods high in methionine include eggs, meat, fish, sesame, Brazil nuts, and cereal grains.

Histidine plays many roles in immunity, gastric secretion and sexual functions. It also protects tissues against damage caused by radiation and heavy metals. Meat, fish, poultry, nuts, seeds and whole grains often contain significant amounts of histidine. 

Leucine, another one of the BCAAs, aids in the regulation of blood-sugar levels, growth and repair of muscle and bone tissue, and growth hormone production. Leucine also helps with wound healing and prevents breakdown of muscle proteins after trauma or severe stress. While all essential amino acids are important for building muscle, leucine is the one that jumpstarts muscle building. The National Library of Medicine notes that a leucine deficiency is rare, as leucine is available in many foods (cheese, soybeans, beef, chicken, pork, nuts, seeds, quinoa, fish, seafood, beans, etc.). 

Lysine plays an important role in protein synthesis, hormone and enzyme production and the absorption of calcium. It also aids in the production of collagen and elastin, which are important components of the skin and connective tissue. Popular protein foods like lean beef, chicken, pork, fish, shellfish, tofu, cheese, milk, beans, lentils and peas contain lysine. 

Foods that contain all nine of these essential amino acids are referred to as complete proteins. A complete protein is a protein that provides all of the essential amino acids in sufficient proportions to support the body. As you might have caught on from the foods listed above, most animal sources of protein — such as meat, poultry, fish, eggs and dairy — deliver all the amino acids your body needs. Plant-based protein sources — such as grains, beans, vegetables and nuts — often lack one or more of the essential amino acids; however, that doesn’t mean you have to eat animal protein products to get all nine essential amino acids and meet your amino acid requirements. You just have to ensure your diet includes a variety of plant-based sources of protein to create complementary amino acids consumption. Soy, while low in methionine, is the only plant-based amino acid containing all the essential amino acids. Protein quality is a measurement of absorption, essential amino acids present, and the level of each amino acid. Complimentary plant-based proteins can help your body get all the essential amino acids it needs from the different foods you consume. Plant-based protein food sources include tofu, tempeh, edamame, lentils, chickpeas, peanuts, almonds, quinoa, chia seeds, beans, potatoes and dark-colored, leafy greens and vegetables.

Getting those essential amino acids: Supplementing with protein powder

If you need help getting the essential amino acids through your diet, consider supplementation. People often supplement with protein powder to ensure they’re getting all nine essential amino acids and help better meet their body’s needs. A 2011 study titled “Clinical use of amino acids as dietary supplement: pros and cons” published in The Journal of Cachexia, Sarcopenia and Muscle determined that essential amino acid supplementation is beneficial in many situations and is an efficient method to increase efficiency of nitrogen supply. A 2017 study published in the peer-reviewed journal Metabolism also found essential amino acid supplements aid in the prevention and treatment of muscle wasting in healthy older adults. 

With so many different forms of protein powder out there, it can be difficult to find one that’s tailored specifically to what you need. That’s where Gainful comes in. Gainful creates a customized protein supplement based on your dietary needs and restrictions, as well as your body type, activity level and fitness goals. You just take a quiz to find your personalized blend of ingredients, and Gainful takes care of the rest. 

Whey protein powder is one of the most popular types of protein powder. Whey is a complete protein, containing more of the BCAAs leucine, isoleucine and valine that are important for muscle building. Unlike other forms of protein, whey protein is quickly absorbed, so your body can immediately begin its muscle repair and rebuilding process. For many people, however, there’s a major downside to whey protein: It contains dairy. Whey is the by-product of cheese production. During cheesemaking, special enzymes are added to heated milk. These enzymes cause the casein in milk to change to a solid state and separate from a liquid substance. That liquid substance is the whey protein, which is washed and dried into a powdered form to become supplements. For people who are strictly plant-based or dairy-free, this renders whey protein a non-option. Fortunately, whey protein isn’t the only quality protein powder type available through Gainful. There are many different dairy-free protein powder options, and two of the most common ones are pea protein and brown rice protein.

Both pea protein and brown rice protein are great dairy-free options. They each have their own set of pros and cons: Pea protein is low in methionine but is lysine-rich, whereas brown rice protein is low in lysine but contains methionine. People often choose to combine the two to create a complete plant-based protein regimen that includes all nine essential amino acids. Gainful is able to combine pea protein and brown rice protein in a ratio that makes a nutritionally complete blend and mirrors the optimal amino acid profile of whey protein — no animal products involved. 

We’ve covered the basics of essential and nonessential amino acids, but if you still have questions, every Gainful subscriber has unlimited access to a personal Registered Dietitian. Your R.D. can answer any remaining questions you may have about essential amino acids, nonessential amino acids and proper supplementation. From those amino acids to pre-workout and hydration formulas, Gainful is here to help you get exactly what your body needs.