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A Guide to the 9 Essential Amino Acids and Why We Need Them

That word “essential” is pretty serious. Surely if you saw “non-essential amino acids,” you wouldn’t be here to learn more.

Yup, essential amino acids are something you need to be aware of if you weren’t already. Amino acids are often referred to as the building blocks of proteins; they’re compounds that play many critical roles in your body. You need essential amino acids for vital processes such as building proteins, hormones, and neurotransmitters.

There are nine essential amino acids, each of which has its unique properties. For example, while some essential amino acids are extra important for muscle development, others play a greater role in collagen production or regulating mood. Because each amino acid has unique properties, you can use particular ones according to your needs.

Where to Find Essential Amino Acids

You can find many of the amino acids you’re looking for in the animal proteins you eat every day, like beef, eggs, fish, dairy, and poultry— though you don’t have to rely on animal sources for your amino acids. 

If you’re vegetarian, vegan, or just worried about meats' cholesterol and saturated fats, you can also obtain essential amino acids from plant-based foods. Plants are often overlooked as a good source of amino acids because most don't contain all nine essential amino acids (or at least not in adequate proportions), but we’ll let you in on a little secret … some do!

When it comes to plant-based eating, there are few sources of complete proteins with all nine essential amino acids. Quinoa, buckwheat, and our personal favorite, soy,  offer all the amino acids you need. Beyond these three foods, other plant-based foods provide some of the essential amino acids, but they aren’t “complete.” 

Although each essential amino acid is… well… essential, learning more about their individual properties and roles in the body can help you take full advantage of their benefits. Here are the details you need on each essential amino acid and which of your favorite foods grant you their benefits:

A Guide to the 9 Essential Amino Acids infographic by Soylent

The 9 Essential Amino Acids


Histidine is needed for several functions, the main one being the growth and repair of tissue. 


Good animal-based sources of histidine: beef, lamb, pork, chicken, turkey, tuna, salmon, cheese, yogurt, milk, eggs

Good plant-based sources of histidine: tofu, soybeans, beans, lentils, pumpkin seeds, sunflower seeds, peanuts, quinoa, wild rice, brown rice, spirulina, wheat germ

Woman working out on the floor


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


  • Is crucial for the production of hemoglobin, a protein in red blood cells that carries oxygen throughout the body
  • Helps regulate blood sugar and energy levels by increasing the body's ability to utilize glucose during exercise

Good animal-based sources of isoleucine: beef, lamb, pork, poultry, tuna, seafood (tuna, cod, haddock), eggs, milk, yogurt, cheese

Good plant-based sources of isoleucine: soybeans, beans, lentils, oats, dried spirulina, seaweed, sunflower & sesame seeds


Leucine is another of the three branched-chain amino acids (BCAAs) that the body uses for muscle repair and growth. In fact, leucine has been studied to enhance strength performance, and it's often considered the most important amino acid for building muscle mass. 


Animal-based sources of leucine: cheese, beef, lamb, poultry, pork, tuna, shrimp, gelatin, collagen

Plant-based sources of leucine: soybeans, beans, lentils, pumpkin seeds, sunflower seeds, pistachios, almonds, peanuts, spirulina, corn, wheat germ, quinoa, brown rice


Lysine helps produce various hormones, enzymes, and antibodies that help you function at your best.


  • Plays an important role in the immune system and has antiviral properties
  • Is crucial for the production of collagen (the protein in the body that gives structure to ligaments, tendons, skin, hair, nails, cartilage, organs, bones, and more). 
  • Lysine plays a role in mental health, too, with one study finding that supplementation of lysine, reduced anxiety and levels of cortisol

Animal-based sources of lysine: beef, lamb, poultry, pork, tuna, shrimp, cheese, eggs, gelatin, collagen

Plant-based sources of lysine: soybeans, pumpkin seeds, pistachios, lentils, beans, oats, wheat germ, quinoa, spirulina


Methionine is a sulfur-containing compound. 


  • Acts as an antioxidant in the body, protecting cells from free radical damage
  • Helps remove lead and mercury from the body
  • Plays a role in maintaining healthy liver function
  • Helps enhance the tone and elasticity of skin and strengthens your hair and nails
  • Helps break down fat, preventing fatty deposits in the liver

Animal-based sources of methionine: beef, lamb, pork, poultry, tuna, salmon, shrimp, eggs, cheese, yogurt, milk

Plant-based sources of methionine: Brazil nuts, soybeans, tofu, beans, lentils, quinoa, wheat germ, spirulina, peanuts


Funny enough, 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.

Phenylalanine and Tyrosine…

  • Help produce dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline) in order to regulate mood and emotional response, as well as the body's fight-or-flight response.

Animal-based sources of phenylalanine: beef, lamb, pork, poultry, cheese, tuna, salmon, eggs, milk, yogurt, gelatin, collagen

Plant-based sources of phenylalanine: soybeans, tofu, pumpkin seeds, peanuts, almonds, pistachios, cashews, quinoa, wild rice, brown rice, oats, wheat germ, spirulina

Woman working out on the floor


Threonine plays a central role in the production of collagen and elastin, the proteins found in connective tissue.


Animal-based sources of threonine: beef, lamb, pork, poultry, salmon, tuna, shrimp, cheese, gelatin, collagen

Plant-based sources of threonine: soybeans, tofu, pumpkin seeds, sunflower seeds, flaxseeds, peanuts, pistachios, cashews, almonds, beans, lentils, spirulina, wheat germ

Two people looking at a phone


Tryptophan is a precursor to serotonin and melatonin, feel-good neurotransmitters essential in regulating appetite, sleep, mood, and pain.


  • Can help regulate food cravings
  • Helps regulate your sleep and wake cycles
  • Is effective at relieving symptoms of premenstrual syndrome
  • Supports the production of niacin (vitamin B3), which is involved in metabolism and helps convert macronutrients from the diet into energy for the body.

Animal-based sources of tryptophan: poultry, beef, lamb, pork, tuna, salmon, shrimp, cheese, eggs

Plant-based sources of tryptophan: soybeans, tofu, beans, lentils, pumpkin seeds, chia seeds, pistachios, cashews, almonds, wheat germ, oats, spirulina


Valine is the last of the three branched-chain amino acids (BCAAs), and the body uses it 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. 


Animal-based sources of valine: beef, lamb, pork, poultry, tuna, salmon, cheese, eggs, milk, yogurt, gelatin, collagen

Plant-based sources of valine: soybeans, mushrooms, pumpkin seeds, sunflower seeds, pistachios, cashews, wild rice, quinoa, brown rice, beans, lentils, oats, cooked broccoli, wheat germ, spirulina

Hand grabbing Soylent drink out of fridge

Supplementing Essential Amino Acids

Now that we’ve got all the facts and tidbits out of the way, it’s time to put them to use. You need to be eating a diverse range of foods to get in all of your essential amino acids — or you can turn to the protein sources that carry them all, like soy.

Supplementation may be the solution if you’re not getting adequate amounts of the nine essential amino acids.

Of course, eating a variety of protein sources can help complete your diet, but quality protein powders like Soylent simplify things and offer all-in-one nutrition. Soy protein is one of the few naturally complete proteins and contains an adequate proportion of each of the nine essential amino acids.

At Soylent, we’ve promised to offer complete nutrition, which is why we use soy protein isolate in our powders and drinks. With soy, we can ensure you’re getting the essential amino acids needed to build muscle, uplift your gut health, support your immune system, and so much more.


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