How Many Amino Acids Are Essential in Humans: A Comprehensive Guide

January 13, 2026 •

3 min read

For a healthy adult, there are nine amino acids considered essential because the human body cannot produce them and must obtain them through diet. While the total number of amino acids is 20, understanding how many amino acids are essential in humans is key to building a balanced and nutritious diet.

Quick Summary

This article explains that humans require nine essential amino acids from dietary sources. It explores the difference between essential, non-essential, and conditionally essential amino acids, listing each category. The text also details the function of these vital compounds and their importance for overall health.

Key Points

Nine Essential Amino Acids: There are nine amino acids that humans must get from their diet because the body cannot produce them in sufficient quantities.
Conditionally Essential: Some amino acids become essential during periods of illness, stress, or rapid growth when the body's synthesis is insufficient.
Complete Proteins: Foods like meat, eggs, and soy are complete proteins, meaning they contain all nine essential amino acids.
Incomplete Proteins: Many plant-based foods are incomplete but can be combined to form a complete amino acid profile.
Deficiency Consequences: A lack of essential amino acids can lead to decreased immunity, muscle loss, and other serious health issues.
Diverse Diet is Key: Eating a varied diet is the best way to ensure you receive all the necessary amino acids for your body's functions.

The Fundamental Building Blocks of Protein

Amino acids are organic compounds that serve as the building blocks for proteins in the human body. When you consume protein-rich foods, your body breaks them down into individual amino acids, which are then used to create new proteins for a variety of critical functions, such as building muscle, synthesizing hormones and enzymes, and transporting nutrients. There are 20 standard amino acids that make up the proteins found in the body, but their classification is what causes confusion.

Essential vs. Non-Essential Amino Acids

The primary difference between essential and non-essential amino acids lies in their origin. The body can produce non-essential amino acids on its own, meaning they don't necessarily need to be obtained directly from your diet. Conversely, essential amino acids must be consumed through food because the body cannot synthesize them in sufficient quantities to meet its needs.

The Nine Essential Amino Acids

It is now well-established in nutritional science that there are nine essential amino acids. While early research focused on seven or eight, histidine is now universally recognized as essential for both infants and adults.

Here are the nine essential amino acids:

Histidine: Plays a vital role in synthesizing histamine, a neurotransmitter that affects immunity, digestion, and sleep.
Isoleucine: Important for muscle metabolism and regulating blood sugar.
Leucine: Crucial for muscle protein synthesis and repair.
Lysine: Essential for building muscle, producing hormones and enzymes, and absorbing calcium.
Methionine: Important for metabolism and detoxification.
Phenylalanine: The precursor for tyrosine, which produces neurotransmitters like dopamine and adrenaline.
Threonine: A key component of structural proteins like collagen and elastin.
Tryptophan: Necessary for producing serotonin and melatonin, which regulate mood and sleep.
Valine: Crucial for muscle growth, tissue repair, and energy production.

The Role of Conditionally Essential Amino Acids

Adding another layer of complexity are the conditionally essential amino acids. These are typically non-essential but become essential during specific circumstances, such as stress, illness, injury, or rapid growth. For example, a person recovering from severe burns may not be able to produce enough of a particular amino acid, making dietary intake temporarily critical.

Examples of conditionally essential amino acids include:

Arginine
Cysteine
Glutamine
Glycine
Proline
Serine
Tyrosine

Complete vs. Incomplete Protein Sources

Foods are often categorized as either complete or incomplete protein sources based on their amino acid profile. Complete protein sources provide all nine essential amino acids, while incomplete sources lack one or more. Animal products like meat, eggs, and dairy are classic examples of complete proteins. Many plant-based foods, such as grains and legumes, are incomplete but can be combined to form a complete protein profile over the course of a day.

Comparison of Amino Acid Types


Feature	Essential Amino Acids	Non-Essential Amino Acids	Conditionally Essential Amino Acids
Body Synthesis	Cannot be produced by the body in sufficient amounts.	Can be produced by the body.	Can be produced by the body but not enough during certain conditions.
Dietary Requirement	Must be obtained from food sources.	Not strictly required from dietary sources.	Required during specific times like illness or rapid growth.
Number (Healthy Adult)	9	11	Varies depending on health status
Example	Leucine, Lysine, Tryptophan	Alanine, Asparagine, Glutamic acid	Arginine, Glutamine, Tyrosine

The Consequences of Deficiency

An amino acid deficiency, particularly of an essential one, can have serious health consequences. Since proteins are vital for nearly every function in the body, a shortfall can impact muscle repair, immune function, and mental alertness. In extreme cases, severe malnutrition can lead to conditions like kwashiorkor or marasmus. Fortunately, a balanced and varied diet usually provides all the essential amino acids needed for a healthy lifestyle. Individuals following vegetarian or vegan diets should ensure they consume a variety of plant-based protein sources to meet all their requirements throughout the day. For detailed information on amino acid biochemistry, consult authoritative sources like the National Institutes of Health. [https://www.ncbi.nlm.nih.gov/books/NBK557845/]

Conclusion

In summary, the human body needs nine essential amino acids that it cannot produce itself. The popular numbers 5, 10, 18, and 20 are inaccurate representations. The confusion likely arises from mistaking the total number of amino acids (20) or other classifications, such as the conditionally essential category. Ensuring a diet rich in a variety of protein sources, both complete and thoughtfully combined incomplete ones, is the best strategy to guarantee an adequate intake of all the essential building blocks your body requires for optimal health.

Frequently Asked Questions

The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Essential amino acids cannot be produced by the human body and must be obtained from food, while non-essential amino acids can be synthesized by the body.

A conditionally essential amino acid is one that is normally non-essential but becomes necessary from the diet during times of illness, stress, or rapid growth when the body can't produce enough.

A deficiency in essential amino acids can lead to various health problems, including slowed growth in children, decreased immunity, fatigue, and digestive issues.

Complete protein sources, which contain all nine essential amino acids, include animal products like meat, fish, eggs, and dairy, as well as plant-based options like quinoa and soy.

Yes, vegetarians and vegans can get all essential amino acids by consuming a variety of plant-based foods throughout the day. Combining different incomplete proteins, like rice and beans, ensures a complete profile.

No, it is not necessary to consume a complete protein at every meal. The body can draw from a pool of amino acids consumed throughout the day, as long as a variety of protein sources are eaten.

The 20 amino acids include the 9 essential ones, the 11 non-essential ones, and the conditionally essential ones that fall into either category depending on the person's health.