Understanding the 20 Amino Acids: Separating Essential from Nonessential

December 28, 2025 •

3 min read

The human body requires 20 distinct amino acids for proper functioning, with protein synthesis being a core function that depends on them. The misconception that there are 20 types of essential amino acids is common, but in fact, only nine are truly essential and must be obtained through your diet.

Quick Summary

An overview of the 20 protein-building amino acids, distinguishing the nine essential ones obtained from diet from the eleven nonessential ones the body synthesizes. The article also covers conditionally essential amino acids and the roles of each amino acid in human health and development.

Key Points

Not 20 Essential: There are 20 protein-building amino acids in total, but only 9 are truly essential and must be consumed through diet.
Body Can Synthesize: The 11 nonessential amino acids can be produced by the human body itself, making dietary intake less critical.
Conditionally Essential: Certain nonessential amino acids become essential during periods of illness, stress, or rapid growth due to higher demand.
Complete Proteins: Animal products and some plant-based foods like soy and quinoa are 'complete' proteins, providing all 9 essential amino acids.
Variety is Key: Plant-based diets require a variety of protein sources (complementary proteins) to ensure all essential amino acids are consumed daily.
Crucial Functions: Amino acids are fundamental for protein synthesis, hormone production, immune function, tissue repair, and muscle growth.

The concept of "essential" amino acids refers to those our bodies cannot synthesize from other compounds, making it necessary to acquire them from food. While all 20 standard amino acids are crucial for health, it is their source that determines their classification. Here, we clarify the roles and sources of all 20 amino acids.

The 9 Essential Amino Acids

These nine amino acids must be acquired through the diet, as the human body cannot produce them on its own. A complete protein source contains all nine, while incomplete proteins lack one or more. They play critical roles in various bodily functions, including protein synthesis, hormone production, and immune response.

Histidine: Involved in producing histamine and is considered conditionally essential in some cases.
Isoleucine: A branched-chain amino acid (BCAA) important for muscle metabolism and immune function.
Leucine: A BCAA vital for muscle protein synthesis and blood sugar regulation.
Lysine: Essential for hormone/enzyme production, calcium absorption, and collagen formation.
Methionine: Involved in metabolism, detoxification, and mineral absorption.
Phenylalanine: A precursor for important neurotransmitters.
Threonine: A component of structural proteins like collagen and supports immune function.
Tryptophan: A precursor for serotonin, affecting mood, appetite, and sleep.
Valine: A BCAA necessary for muscle growth, tissue regeneration, and energy.

The 11 Nonessential Amino Acids

These amino acids can be synthesized by the human body. While the body can produce them, dietary intake is still beneficial. They are involved in numerous processes from detoxification to neurotransmitter function.

Alanine: Aids in toxin removal and glucose production.
Asparagine: Transports nitrogen and helps synthesize DNA.
Aspartic Acid (Aspartate): Key in metabolism and synthesizing other amino acids.
Glutamic Acid (Glutamate): A crucial brain neurotransmitter.
Glycine: Supports cell growth, wound healing, and acts as a neurotransmitter.
Proline: Important for tissue repair and collagen formation.
Serine: Promotes muscle growth and immune protein synthesis.
Cysteine: Functions as an antioxidant and aids collagen production.
Glutamine: Supports brain function and nucleic acid synthesis.
Arginine: Involved in protein/hormone synthesis and immune function.
Tyrosine: Important for thyroid hormones and neurotransmitter synthesis.

Conditionally Essential Amino Acids

Some nonessential amino acids can become "conditionally essential" when the body's need exceeds its production capacity, such as during illness, stress, or rapid growth. Examples include arginine, cysteine, glutamine, glycine, proline, and tyrosine.

Comparison of Amino Acid Types


Feature	Essential Amino Acids	Nonessential Amino Acids
Source	Must be consumed through diet.	Can be synthesized by the body.
Quantity	There are 9.	There are 11.
Deficiency Risk	Higher probability if dietary intake is insufficient.	Deficiency is rare but can occur with starvation or illness.
Dietary Importance	Crucial for obtaining all necessary building blocks for proteins.	Still beneficial to consume from food, as it can spare the body from expending energy on synthesis.
Example	Leucine, Lysine, Tryptophan.	Alanine, Glycine, Serine.

Obtaining All 20 Amino Acids

A balanced diet is the best way to ensure intake of all amino acids. Complete protein sources, like animal products, soy, quinoa, and buckwheat, contain all nine essential amino acids. Vegetarians and vegans can combine incomplete protein sources, like legumes and grains, to obtain a complete essential amino acid profile. Supplements are an option but usually not necessary with a varied diet.

Conclusion

All 20 amino acids are vital for health. The key difference lies in whether our body can synthesize them (nonessential) or if they must come from our diet (essential). Ensuring adequate intake of the 9 essential amino acids through a varied diet of complete and complementary proteins supports crucial bodily functions.

For more detailed information on amino acids, resources like the National Center for Biotechnology Information are available.

Frequently Asked Questions

The main difference is whether the human body can produce them. Essential amino acids cannot be produced internally and must be obtained through the diet, while nonessential amino acids can be synthesized by the body.

A common mnemonic to remember the nine essential amino acids is "PVT TIM HALL". This stands for: Phenylalanine, Valine, Tryptophan, Threonine, Isoleucine, Methionine, Histidine, Arginine*, Leucine, and Lysine. Note: Arginine is technically conditionally essential for adults.

Conditionally essential amino acids are typically nonessential but become essential during periods of illness, stress, trauma, or rapid growth when the body cannot produce enough to meet its needs. Examples include arginine, cysteine, and tyrosine.

Yes. While many plant-based foods are incomplete proteins, a varied diet that includes a range of complementary protein sources like legumes, grains, nuts, and seeds throughout the day can easily provide all nine essential amino acids.

No. A single protein molecule does not necessarily contain all 20 amino acids. Each protein has a specific sequence of amino acids determined by DNA, and this sequence can use a selection of the available 20 to create its structure.

A deficiency in essential amino acids can lead to various health problems. Symptoms may include fatigue, reduced immune response, muscle weakness, loss of muscle mass, and issues with hair and skin health.

For most people, obtaining amino acids from a balanced diet of whole foods is sufficient and preferable. Whole food sources provide a full spectrum of nutrients. Supplements may be beneficial for athletes, individuals with certain dietary restrictions, or those with increased needs due to illness.