How many amino acids are essential to include in a person's diet?

December 27, 2025 •

3 min read

Approximately 50% of the world's population living in poor regions lacks adequate protein, highlighting the importance of understanding essential nutrients. A healthy adult body cannot produce all the amino acids it needs, necessitating the inclusion of essential amino acids in a person's diet through food.

Quick Summary

Nine specific amino acids cannot be synthesized by the adult human body and must be obtained through food. They are crucial for protein synthesis, tissue repair, and hormone production. Dietary sources include animal products and various plant-based foods, and a deficiency can lead to numerous health issues.

Key Points

Nine Essential Amino Acids: The adult human body requires nine specific amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) from dietary sources because it cannot produce them internally.
Protein Building Blocks: Amino acids combine to form proteins, which are critical for virtually all physiological functions, including muscle repair, tissue growth, and the production of hormones and neurotransmitters.
Complete vs. Incomplete Proteins: Complete protein sources (e.g., meat, dairy, eggs, soy, quinoa) contain all nine essential amino acids, while incomplete sources (most plants) lack one or more.
Complementary Plant-based Proteins: Individuals on vegetarian or vegan diets can obtain all essential amino acids by consuming a variety of plant-based protein sources, such as combining legumes and grains.
Deficiency Risks: Inadequate intake of essential amino acids can lead to severe health issues, including fatigue, muscle atrophy, impaired growth, weakened immune function, and mood disturbances.
Conditionally Essential Amino Acids: Some amino acids become essential during periods of illness, stress, or rapid growth when the body's need outstrips its production capacity.
Balanced Diet is Key: Relying on a varied and balanced diet, rather than supplements alone, is the most effective way to ensure consistent intake of all necessary essential amino acids.

What are Amino Acids and Why are They So Important?

Amino acids are the building blocks of proteins, which are vital for numerous bodily functions. The human body requires 20 different amino acids. These are categorized as essential, non-essential, or conditionally essential based on whether the body can produce them or if they must be obtained from the diet. Essential amino acids are particularly critical as the body cannot synthesize them internally. Proteins formed from these amino acids are involved in processes ranging from muscle growth to immune function.

The Nine Essential Amino Acids Your Body Can’t Produce

For a healthy adult, nine amino acids are considered essential and must be obtained through diet. These are crucial because the body lacks the ability to synthesize them. A balanced diet ensures adequate intake of these nine essential amino acids, which serve various vital functions in the body:

Histidine: Supports immune response and nerve function.
Isoleucine: Important for muscle metabolism.
Leucine: Crucial for protein synthesis and muscle repair.
Lysine: Aids in calcium absorption and hormone production.
Methionine: Involved in metabolism and detoxification.
Phenylalanine: Precursor for neurotransmitters.
Threonine: A component of structural proteins.
Tryptophan: Precursor for serotonin, influencing mood and sleep.
Valine: Supports muscle growth and tissue regeneration.

Complete vs. Incomplete Protein Sources

Protein sources are classified as 'complete' if they contain all nine essential amino acids in sufficient amounts, and 'incomplete' if they are missing one or more.

Complete Protein Sources (Examples)

Meat and poultry
Fish and seafood
Eggs and dairy
Quinoa and soy products

Incomplete Protein Sources (Examples)

Legumes, nuts, and seeds
Most grains and vegetables

A varied plant-based diet, combining different incomplete protein sources like rice and beans, can provide all essential amino acids over the course of the day.

Health Implications of Essential Amino Acid Deficiency

Inadequate intake of essential amino acids hinders the body's ability to build necessary proteins for essential functions. Chronic deficiency can result in various health issues.

Physical Symptoms: May include fatigue, weakness, impaired growth, and muscle atrophy.
Weakened Immunity: Essential amino acids are needed for antibody production, increasing susceptibility to illness.
Mental Health Impact: Deficiency can affect neurotransmitter production, potentially contributing to mood disorders.
Tissue Health: Can negatively impact skin, hair, and connective tissue health.

The Role of Conditionally Essential Amino Acids

Beyond the nine essential amino acids, some non-essential amino acids can become 'conditionally essential' when the body's need surpasses its production capacity, such as during illness, stress, or rapid growth. Examples include arginine, cysteine, and glutamine.

Comparison Table: Essential vs. Conditionally Essential vs. Non-essential Amino Acids


Feature	Essential Amino Acids	Conditionally Essential Amino Acids	Non-essential Amino Acids
Body Production	Cannot be synthesized by the body.	Production may be insufficient during illness or stress.	Synthesized by the body in sufficient quantities under normal conditions.
Dietary Requirement	Always required via diet.	Required in certain situations (e.g., illness, stress).	Not required from the diet under normal circumstances.
Number (for humans)	Nine.	Six.	Six.
Key Dietary Sources	Found in complete proteins (meat, eggs, soy).	Varies, found in protein-rich foods.	Can be created internally.

Conclusion: Ensuring Adequate Intake is Key

Nine amino acids are essential for adult humans as they cannot be produced internally and must be obtained from food. A balanced diet with various protein sources is crucial for ensuring sufficient intake of all nine. Complete proteins, often from animal sources, provide all essential amino acids, while plant-based diets can combine incomplete proteins to meet these needs. Adequate essential amino acid intake is fundamental for overall health, supporting tissue repair, immune function, mood regulation, and hormone production.

For additional authoritative information on the subject, please visit the Harvard T.H. Chan School of Public Health website https://nutritionsource.hsph.harvard.edu/what-should-you-eat/protein/.

Frequently Asked Questions

The main difference is that essential amino acids cannot be produced by the human body and must be acquired through diet, whereas non-essential amino acids can be synthesized internally from other amino acids or substrates.

Vegetarians and vegans can get all essential amino acids by eating a variety of plant-based foods throughout the day. Combining different incomplete protein sources, like rice and beans, provides all nine essential amino acids.

Complete protein sources are foods that contain all nine essential amino acids in sufficient quantities. Examples include meat, poultry, fish, eggs, dairy, soy products, and quinoa.

A deficiency in essential amino acids can lead to a range of health problems, including fatigue, decreased immunity, slowed growth, muscle loss, and mood disorders.

For most people consuming a healthy, balanced diet, amino acid supplements are not necessary. It is generally better to obtain these nutrients from food sources. Consult a healthcare provider before taking any supplements.

Conditionally essential amino acids are normally non-essential but become essential during certain conditions like illness, injury, or severe stress when the body cannot produce them in sufficient amounts.

The human body needs a total of 20 different amino acids to grow and function properly, including the nine essential ones and the 11 non-essential ones it can produce itself.