Essential Amino Acids


Essential Amino Acids

Proteins are the building blocks of life. Protein occurs in all living cells and has both functional and structural properties. It's an essential part of the diet as it helps the body to repair cells and make new ones.

Protein exists in both plants and animals. When digested it's broken down into amino acids, of which there are three types:

There are nine essential amino acids, including three branched chain amino acids. These cannot be produced by the body and must be consumed from diet. They are leucine, isoleucine, valine (branched chain) and histidine, lysine, methionine, phenylalanine, threonine and tryptophan.

The body is able to breakdown proteins and other amino acids to make these. They include alanine, asparagine, aspartic acid and glutamic acid.

Are needed in times of stress, illness, or intense physical exercise. They include arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline and serine.

Essential Amino Acids

For this article we'll be focussing on the nine key amino acids that the body cannot produce and are relied on from dietary consumption.

The best sources of essential amino acids are eggs, meat, chicken, dairy (whey), seafood, and other animal sources. They can also be found in plant sources such as beans (soy, black, pinto), some nuts (walnuts, almonds), lentils, chickpeas, and of course in our pea isolate protein powder which has a concentrated amount.

For those undergoing intense physical training between 1.5 and 2 grams of total protein per kilogram of body weight is recommended to build muscle mass. Of course protein dietary needs vary depending on a range of factors including intensity of training, age, sex, goals, and so on.


Leucine is one of three branched chain amino acids and is primarily involved in muscle protein synthesis for muscle growth and recovery. It also contributes to the regulation of blood-sugar levels, growth hormone production and wound healing. 

It can be used to enhancing physical performance because it boosts stamina and endurance while delaying the deterioration of muscle tissues through the significant increase in the production of muscle proteins.

"Branched chain amino acids, particularly leucine, stimulate protein synthesis, increase reutilisation of amino acids in many organs and reduce protein breakdown. Leucine also stimulates insulin release, which in turn stimulates protein synthesis and inhibits protein breakdown. These effects are particularly useful in athletic training". Source.

Food sources of leucine include:

  • red meat
  • chicken
  • pork (pork has the ideal ratio of BCAAs)
  • nuts, seeds
  • soy


Isoleucine is another of the three branched chain amino acids. It is known to support blood clotting at wound sites and assisting with muscle tissue repair. Isoleucine can also help to boost energy levels and improve stamina.

"Isoleucine has diverse physiological functions, such as assisting wound healing, detoxification of nitrogenous wastes, stimulating immune function, and promoting secretion of several hormones. Necessary for hemoglobin formation and regulating blood sugar and energy levels, isoleucine is concentrated in muscle tissues in humans". Source.

Food sources of isoleucine include:

  • meats
  • eggs
  • fish
  • cheese
  • nuts, seeds
  • Seaweed


Valine is another branched chain amino acid - the building blocks of proteins produced by cells that are recorded in the genetic code of all living things. It's also involved with muscle growth and repair, as well as energy production.

"Valine is a branched-chain essential amino acid that has stimulant activity. It promotes muscle growth and tissue repair...A glycogenic amino acid, valine maintains mental vigor, muscle coordination, and emotional calm". Source.

Food sources of valine include:

  • soy
  • cheese
  • fish
  • meats
  • vegetables


Histidine is involved in many bodily functions including tissue repair, immune system support, and building haemoglobin.

It is a unique amino acid because it's adults can typically produce enough from other amino acids in the liver, but children need to obtain it from their diet.

"Histidine is a semi-essential amino acid (children should obtain it from food) needed in humans for growth and tissue repair, Histidine is important for maintenance of myelin sheaths that protect nerve cells and is metabolized to the neurotransmitter histamine. Histamines play many roles in immunity, gastric secretion, and sexual functions. Histidine is also required for blood cell manufacture and protects tissues against damage caused by radiation and heavy metals". Source.

Food sources of histidine include:

  • meats (beef, lamb, pork)
  • chicken & turkey
  • fish
  • eggs
  • cheese
  • nuts & seeds
  • beans


Lysine helps in the formation of collagen and elastin, and also helps to prevent it breaking down. Collagen is the connective tissue that accounts for up to 30 percent of proteins in our body. It builds cartilage, bones, forms the elastic netting that supports the protective tissues in joints, and is essential to giving skin elasticity and strength.

Lysine also assists with absorption of calcium by reducing the amount of calcium that's excreted in urine, which promotes the development of bones, nails, teeth, and hair. It has been suggested that Lysine supplementation may be useful in preventing and treating osteoporosis.

Lysine plays a role in energy, hormone, and enzyme production, as well as protein synthesis. It should be consumed by athletes who engage in physical activity.

Lysine may have further potential for reducing cholestorol, improving recovery times after surgery, and for the development of muscle. More research is being conducted.

Food sources of lysine include:

  • Quinoa
  • Cheese & yoghurt
  • Fish (flounder especially)
  • Lean beef and most meats
  • Chicken
  • Soy
  • Eggs
  • Nuts & seeds


Methionine is a sulfur-containing amino acid which plays an important role in protein synthesis and function. As cellular proteins break down, methionine assists in the process of making new proteins. This is especially the case and relevant here in regards to exercise induced muscular hypertrophy. In other words, methionine is need for muscle growth and repair especially with strenuous physical exercise.

It also plays an important role in detoxification and metabolism, and assists with the absorption of the key minerals selenium and zinc.

However, too much methionine may cause a loss of calcium in the body which can require additional calcium supplementation to overcome. It can also contribute towards atherosclerosis (the build up of fats, cholesterol and other substances in artieries).

"Methionine is a sulfur-containing essential L-amino acid that is important in many body functions...Methionine is required for growth and tissue repair. A sulphur-containing amino acid, methionine improves the tone and pliability of skin, hair, and strengthens nails. Involved in many detoxifying processes, sulphur provided by methionine protects cells from pollutants, slows cell aging, and is essential for absorption and bio-availability of selenium and zinc. Methionine chelates heavy metals, such as lead and mercury, aiding their excretion. It also acts as a lipotropic agent and prevents excess fat buildup in the liver." Source.

Food sources of methionine include:

  • Chicken
  • Fish
  • Eggs
  • Red meat
  • Milk
  • Vegetables, nuts, beans and grains have smaller amounts


Phenylalanine is found in three forms - L-phenylalanine, D-phenylalanine, and DL-phenylalanine. L-phenylalanine is used by the body in the structure and functions of proteins and enzymes, and to make other amino acids such as tyrosine which plays a role in protein synthesis.

"Phenylalanine is an essential aromatic amino acid in humans (provided by food), Phenylalanine plays a key role in the biosynthesis of other amino acids and is important in the structure and function of many proteins and enzymes. Phenylalanine is converted to tyrosine, used in the biosynthesis of dopamine and norepinephrine neurotransmitters. The L-form of Phenylalanine is incorporated into proteins, while the D-form acts as a painkiller". Source.

Food soucres of phenylalanine include:

  • Soy
  • Meat (beef & lamb)
  • Tuna
  • Chicken & turkey
  • Eggs
  • Milk
  • Beans
  • Nuts & seeds (pumpkin)


Threonine is involved in the growth and development of skeletal muscles, intestines, and liver. It can help to build strong bones which can help in wound and injury recovery.

It's also a key part of structural proteins such as collagen and elastin. Collagen is the connective tissue that accounts for up to 30 percent of proteins in our body. It builds cartilage, bones, forms the elastic netting that supports the protective tissues in joints, and is essential to giving skin elasticity and strength.

Threonine also assists with the metabolism of fats and in the immune system by producing antibodies required for function.

"Threonine is an essential amino acid in humans (provided by food), Threonine is an important residue of many proteins, such as tooth enamel, collagen, and elastin. An important amino acid for the nervous system, threonine also plays an important role in porphyrin and fat metabolism and prevents fat buildup in the liver." Source.

Food sources of threonine include:

  • Liver
  • Gelatin
  • Chicken
  • Milk & cheese
  • Shellfish
  • Beef & pork
  • Soy


Tryptophan is needed for general growth and development. It helps to maintain nitrogen balance and makes niacin (vitamin B3), and in turn the neurotransmitter serotonin which helps to regulate appetite, sleep, and mood.

"Tryptophan is the least plentiful of all 22 amino acids and an essential amino acid in humans (provided by food), Tryptophan is found in most proteins and a precursor of serotonin. Tryptophan is converted to 5-hydroxy-tryptophan (5-HTP), converted in turn to serotonin, a neurotransmitter essential in regulating appetite, sleep, mood, and pain." Source.

Food sources of tryptophan include:

  • Fish
  • Eggs
  • Red meat
  • Milk, yoghurt & cottage cheese
  • Tofu
  • Chicken & turkey
  • Lentils & beans


All of our protein powders here at NZProtein are complete protein sources. This means, they contain all nine essential amino acids. They also contain the remaining non-essential and condition amino acids required to support essential metabolic function, making them all quality sources of protein to assist muscle repair and development.

Although these needs can be met by eating lean meats, eggs, fish, soy, beans, and so forth - the addition of protein powders makes a convenient way to supplement protein into the diet. Shakes are relatively inexpensive, quick, and easy. Shakes can be easier to digest and absorb than heavier foods, especially for those with sensitive stomachs. And most of the time they're delicious too!

It is best to consume protein from a variety of sources as this will ensure that your body gets all the essential (and non-essential) amino acids and other key nutrients it requires on a daily basis. For more informative reading also see our blog post on animal vs plant protein.