The 9 Essential Amino Acids: Benefits & How To Get Enough Of Them

Amino acids are the foundation of protein—one of the three macronutrients that make up the bulk of the human diet. Here's what you need to know about amino acids, including what each essential one does, both plant and animal sources of each, insight on supplemental amino acids, and the latest on branched-chain amino acids.

"When we consume proteins through food, our body breaks them back down into amino acids, which can be reused to make the proteins the body needs," registered dietitian Lisa Hayim, M.S., R.D. tells mindbodygreen.

"It may be helpful to think of amino acids as the cars on the train," she explains. "Each car is an amino acid, yet the whole train is the protein." 

There are a total of 20 amino acids that human bodies require to produce all the proteins needed to function and grow. Nine of them are called "essential" amino acids: These organic molecules obtained from protein-containing foods are crucial to countless processes in our bodies, including giving cells their structure, forming organs and muscles, repairing tissue, producing energy, and more.

Although animal proteins such as beef, eggs, fish, dairy, and poultry contain good amounts of all nine essential amino acids (making them "complete" proteins), you can also obtain essential amino acids from plant-based foods. While it's true that most plant foods don't contain all nine essential amino acids in adequate proportions, vegetarians and vegans can ensure healthy intake by consuming a variety of plant protein sources over the course of a day. Here's a primer on how to up your protein intake each day.

While you need all 20 amino acids to function optimally, some of these are produced naturally by your body, making them nonessential amino acids1. This means you don't need to obtain them from the foods in your diet.

Others are considered conditionally essential amino acids, meaning that they're nonessential1 (i.e., your body produces them) except under specific circumstances, such as illness or stress.

The nine essential amino acids, on the other hand, cannot be created by the body and must always be obtained from food.

Each of the nine essential amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—has unique properties.

For example, while some essential amino acids are extra important for muscle development, others play a greater role in collagen production2 or regulating mood3. This means it may be particularly beneficial for you to seek certain ones depending on your individual needs. For health conditions including metabolic syndrome and anxiety4, doctors have had success treating patients with therapeutic doses of specific amino acids.

Here is more on each of the nine essential amino acids, including the main roles each one plays in the body and where to find them in your favorite foods:

The essential amino acid histidine is needed for the growth and repair of tissue, particularly for the maintenance of myelin sheaths—sleeves of fatty tissue that protect nerve cells, ensuring that they're able to send and receive messages.

Research shows5 that it even helps protect tissues against damage caused by radiation, and functions as a chelating agent to remove heavy metals from the body.

Histidine has antioxidant and anti-inflammatory properties and has been studied for its protective effects in chronic disease6. It is also a precursor to the neurotransmitter histamine, which plays a vital role in immune functioning and helps produce red and white blood cells.

The essential amino acid isoleucine is one of three branched-chain amino acids (BCAAs), along with leucine and valine, that the body uses for muscle repair and growth.

It's heavily concentrated in the muscle tissue and plays an important role in muscle metabolism, providing your muscles with the appropriate fuel to do work.

Isoleucine is also involved in blood clot formation7 and crucial for the production of hemoglobin, a protein in red blood cells that carries oxygen throughout the body. It helps regulate blood sugar and energy levels by increasing the body's ability to utilize glucose8 during exercise. (Here's how to tell if you have healthy blood sugar.)

The essential amino acid leucine is one of three branched-chain amino acids (BCAAs) that the body uses for muscle repair and growth.

In fact, leucine has been studied to enhance strength performance9 and it's often considered the most important amino acid for building muscle mass. That's partly because leucine appears to be the main amino acid10 responsible for activating mTOR (mammalian target of rapamycin), a signaling pathway that's responsible for stimulating protein synthesis11.

Additionally, leucine helps produce growth hormones; prompts insulin release12, which plays a key role in regulating blood sugar levels and energy levels, and helps promote the healing of muscle tissue, skin, and bones after trauma or severe stress.

Learn more about foods high in leucine here.

The essential amino acid lysine helps produce various hormones, enzymes, and antibodies.

It plays an important role in the immune system and has antiviral properties, with some research suggesting that it may be effective against herpes by improving the balance of nutrients in the body in a way that slows the growth of the virus.

Lysine is also crucial for the production of collagen—the most abundant protein in the body that gives structure to ligaments, tendons, skin, hair, nails, cartilage, organs, bones, and more.

Experts suggest that lysine, along with vitamin C and the amino acid proline, are essential for the formation of healthy collagen. Together, they form procollagen, which is then converted into several different types of collagen found in various tissues throughout the body.

Lysine plays a role in mental health, too, with one study4 finding that supplementation of lysine, along with arginine, reduced anxiety and levels of the stress hormone cortisol.

Learn more about foods high in lysine here.

The essential amino acid methionine is a sulfur-containing compound.

The sulfur provided by methionine plays a powerful antioxidant role13 in the body, protecting cells from free radical damage. Building upon its detoxifying properties, sulfur-containing methionine also chelates heavy metals14 like lead and mercury and helps remove them from the body.

Research15 has shown that methionine also plays a role in helping to maintain healthy liver function.

Along with offering internal protection, methionine helps to improve our appearance by enhancing the tone and elasticity of our skin and strengthening our hair and nails.

Building upon its detoxifying properties, methionine also chelates heavy metals like lead and mercury and helps remove them from the body. It also acts as a lipotropic agent, helping to break down fat, and prevents fatty deposits in the liver. Too much methionine, however, may lead to atherosclerosis, or fatty deposits in the arteries. (Here are nine signs you need a detox.)

The essential amino acid phenylalanine plays a key role in the creation of other amino acids, including tyrosine.

Tyrosine, in turn, has a number of uses in the body, including the production of the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline)—and thus plays a role in regulating mood and emotional response, as well as the body's fight-or-flight response.

One case study16 highlighted the importance of phenylalanine in Parkinson’s Disease because it helps to synthesize tyrosine, dopamine and norepinephrine - all of which are depleted in the disease. It has also been studied for its potential antidepressant properties17, although more research is needed. 

The essential amino acid threonine plays a central role in the production of collagen and elastin, which help provide structure and stretchiness to skin and connective tissues.

It's also found in high concentrations in the central nervous system, and some research suggests it may help reduce symptoms of spasticity 18(when certain muscles are continuously contracted) in multiple sclerosis patients, as well as alleviate anxiety and mild depression19.

Threonine is important for maintaining a healthy gut and digestive tract as well. It's needed to produce the mucus layer that covers the digestive tract, and is important for protecting the integrity of the gut lining against stress20.

Threonine (along with another amino acid serine), also plays an important role in T-cell functioning21 to optimize our immune systems. Additionally, threonine is important for fat metabolism and helps prevent fat buildup in the liver22.

The essential amino acid tryptophan is a precursor to serotonin, a feel-good neurotransmitter essential in regulating appetite, sleep, mood, and pain, and which has natural sedative effects.

Serotonin has actually been shown to reduce appetite and supports a more calm, clear mind meaning that consuming enough tryptophan-containing foods could potentially aid in normalizing food cravings. Tryptophan is also a precursor to melatonin, a hormone which (along with serotonin) regulates our sleep and wake cycles—which is exactly why everyone says you feel sleepy after a big Thanksgiving dinner with lots of tryptophan-rich turkey.

Research23 has found tryptophan to be effective at relieving symptoms of premenstrual syndrome, while low levels have been associated with mood swings, anxiety, and depression. This essential amino acid also supports the production of niacin (vitamin B3), which is involved in metabolism and helps convert macronutrients from the diet into energy for the body.

The essential amino acid valine is one of three branched-chain amino acids (BCAAs), along with isoleucine and leucine, that the body uses for muscle repair and growth.

Like the other two BCAAs, valine helps regulate blood sugar and maintain energy levels by supplying glucose to muscles during workouts. An animal study24 found that supplemental valine contributed to the reduction of fatigue during exercise.

Valine also has stimulant activity and has been said to help maintain mental and physical stamina25, while its role in the central nervous system supports emotional calm. Along with fellow branched-chain amino acids, valine has also been shown to be a useful supplemental therapy in treating liver disease26.

Amino acids, especially the essential ones, should ideally be obtained through your diet. Here is the RDA breakdown per 2.2 lbs of body weight:

To decide, first ask yourself: Are you eating enough protein? If not, then you may not be getting adequate levels of the nine essential amino acids. In that case, start eating more protein from a variety of plant and animal sources, like the ones mentioned above.

If you're a vegetarian or vegan, or anyone who's not confident that your diet is quite cutting it in the protein department, consider supplementing with a quality protein powder, which can easily be added to smoothies, oatmeal, and baked goods.

Whey protein is a naturally complete protein and contains an adequate proportion of each of the nine essential amino acids. Vegan protein powders are typically always complete, too, since they're often made with a variety of different plant proteins (such as a combo of pea, hemp, and brown rice proteins) to cover all your bases, or they're made from soy, one of the few complete plant-based proteins.

RELATED READ: 8 Types Of Protein Powders + How To Find The Best Option (For You & The Planet)

If you're at all into fitness, you've probably heard of branched-chain amino acids, or BCAAs. These are the three essential amino acids—leucine, isoleucine, and valine—that seem to be extra important for maintaining muscle.

Research shows27 that they activate key enzymes that promote muscle growth. The "branched chain" refers to their chemical structure.

Yet, BCAAs may serve other purposes, too. Some experts tout their fatigue-fighting benefits, as research28 shows they can interfere with the transport of the relaxation-inducing amino acid tryptophan, thus preventing you from getting too sleepy.

Amino acids are the building blocks of protein, with 9 of them being essential since we can only get them from our diet. Each of the essential amino acids provides a range of benefits—from reduced stress to muscular repair to gut maintenance. As always, aim to get your essential amino acids from whole foods when possible. Here's a list of high-protein breakfasts to get you started.