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

"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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.