Which amino acids do humans need?

December 26, 2025 •

3 min read

The human body requires 20 different amino acids to function, yet it can only produce 11 of them on its own. This is why understanding which amino acids do humans need is crucial for maintaining a healthy diet, as the other nine must be obtained through food.

Quick Summary

The body needs nine essential amino acids from dietary sources because it cannot produce them internally. Learn about the functions of essential, non-essential, and conditionally essential amino acids, as well as where to find them in your diet.

Key Points

Essential Amino Acids: Humans must obtain nine specific amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—from their diet.
Conditionally Essential Amino Acids: Some non-essential amino acids, such as arginine and glutamine, become necessary to get from the diet during times of illness, injury, or stress.
Complete vs. Incomplete Proteins: Animal products are typically complete proteins, containing all essential amino acids, while most plant-based foods are incomplete but can be combined to form a complete profile.
Role in the Body: Amino acids are not only for muscle building; they are crucial for producing hormones, enzymes, and neurotransmitters, as well as repairing tissues.
Balanced Diet is Key: Most individuals can meet their amino acid needs by eating a varied and balanced diet that includes a mix of protein sources.

Amino acids are the fundamental building blocks of proteins, which are involved in nearly all biological processes in the body, such as muscle building, tissue repair, and the production of hormones and enzymes. Humans require 20 different amino acids, classified into three categories based on how the body obtains them: essential, non-essential, and conditionally essential. Getting a balanced intake is crucial for overall health.

The Nine Essential Amino Acids

Essential amino acids (EAAs) cannot be synthesized by the body and must come from the diet. There are nine EAAs, each with critical roles. Foods containing all nine are called complete proteins. These nine essential amino acids are:

Histidine: Involved in immune response, digestion, and sleep-wake cycles.
Isoleucine: A branched-chain amino acid (BCAA) important for muscle metabolism.
Leucine: Another BCAA vital for protein synthesis and muscle repair.
Lysine: Essential for protein synthesis, hormone production, and calcium absorption.
Methionine: Involved in metabolism, detoxification, and tissue growth.
Phenylalanine: Converted into neurotransmitters like tyrosine and dopamine.
Threonine: A main component of structural proteins like collagen and elastin.
Tryptophan: The precursor to serotonin, which affects mood and sleep.
Valine: The third BCAA, involved in muscle growth and tissue regeneration.

Conditionally Essential Amino Acids

These amino acids are usually non-essential but become essential under specific conditions like illness, injury, or stress when the body's production is limited. Examples include Arginine, Cysteine, Glutamine, Glycine, Proline, and Tyrosine, each with roles like supporting immune function, tissue repair, or being needed during rapid growth or pregnancy.

Non-Essential Amino Acids

Non-essential amino acids (NEAAs) can be produced by the body and don't need to be acquired from the diet under normal conditions. These include alanine, asparagine, aspartic acid, and glutamic acid. All 20 amino acids are necessary for proper bodily function.

The Role of Amino Acids in the Body

Amino acids are vital for numerous physiological functions beyond just building muscle. They are crucial for:

Enzyme and Hormone Production: Creating enzymes for digestion and hormones regulating metabolism and mood.
Tissue Repair and Growth: Essential for healing and maintaining healthy tissues, skin, and hair.
Neurotransmitter Synthesis: Forming chemical messengers important for brain function.
Immune System Support: Building antibodies to fight infections.

Food Sources for Amino Acids

Getting amino acids from food is generally achievable with a varied diet. Complete proteins, like animal products, contain all nine essential amino acids. Plant-based diets can also provide all EAAs by consuming a variety of protein sources throughout the day.

Complete Protein Sources: Eggs, meat, fish, dairy, quinoa, and soy products.
Incomplete Protein Sources (Plant-Based): Nuts, seeds, lentils, beans, and grains. Combining these helps vegans and vegetarians get a complete amino acid profile.

Essential vs. Conditionally Essential vs. Non-Essential Amino Acids


Feature	Essential (EAAs)	Conditionally Essential (CEAAs)	Non-Essential (NEAAs)
Produced by Body?	No, must be from diet.	Under normal circumstances, yes. Under stress/illness, no.	Yes, the body can produce them.
Number of Amino Acids	9	Varies (e.g., Arginine, Cysteine, Glutamine).	11
Dietary Requirement	Always required via diet.	Required only under certain conditions (illness, growth).	Not required via diet for healthy adults.
Key Examples	Leucine, Lysine, Tryptophan.	Arginine, Tyrosine, Cysteine.	Alanine, Glycine, Serine.

Conclusion

To function optimally, the human body needs 20 amino acids. While 11 are produced internally, the nine essential amino acids must come from a balanced diet. Some non-essential amino acids become conditionally essential during periods of stress or illness. A diverse diet with various protein sources is the best way to ensure adequate amino acid intake for protein synthesis, tissue repair, and other vital processes.

For more detailed information on essential amino acids and dietary recommendations, consult the Recommended Dietary Allowances from the National Institutes of Health.

Frequently Asked Questions

The main difference is that essential amino acids cannot be produced by the body and must be consumed through the diet, whereas non-essential amino acids can be synthesized internally.

There are nine essential amino acids that humans must acquire from their diet: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Yes, vegetarians and vegans can get all essential amino acids by consuming a variety of plant-based protein sources throughout the day, which ensures all nine are acquired.

Complete protein sources contain all nine essential amino acids. Examples include meat, poultry, fish, eggs, dairy products, soy, quinoa, and buckwheat.

A deficiency in essential amino acids can lead to various issues, including negative effects on growth and overall health, potentially resulting in conditions like malnutrition.

For most people consuming a healthy, balanced diet, supplements are not necessary. However, some may use them for specific goals like enhancing athletic performance or mood, but consulting a healthcare provider is recommended.

Certain amino acids, like arginine and glutamine, are considered conditionally essential. They become 'essential' during specific physiological stresses, such as during illness, injury recovery, or in infants, when the body cannot produce them in sufficient quantities.