How many amino acids are supplied by diet?

December 12, 2025 •

3 min read

The human body requires 20 amino acids to function, yet it can only produce 11 of them. This means you must obtain the remaining nine essential amino acids through your diet.

Quick Summary

This article explains why nine essential amino acids must be consumed through food, detailing their functions and food sources. It also covers non-essential and conditionally essential amino acids, dietary protein classifications, and the importance of a balanced diet for overall health.

Key Points

Nine Essential Amino Acids: Your diet must supply nine specific essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) because your body cannot produce them.
Eleven Non-Essential Amino Acids: Your body synthesizes 11 other amino acids, so they are not essential in your diet under normal circumstances.
Complete vs. Incomplete Proteins: Foods with all nine essential amino acids are complete proteins (e.g., meat, soy), while those missing one or more are incomplete (e.g., nuts, seeds).
Combine Incomplete Proteins: Plant-based eaters can meet their essential amino acid needs by eating a variety of incomplete protein sources throughout the day.
Conditionally Essential Amino Acids: Under stress, illness, or rapid growth, some non-essential amino acids like arginine and glutamine may become conditionally essential and need dietary support.
Functions in the Body: Essential amino acids are vital for countless processes, including muscle repair, hormone production, immune function, and regulating mood.
Dietary Balance is Key: A balanced diet rich in varied protein sources is the best strategy to ensure adequate intake of all necessary amino acids.

The Essentials: Nine Amino Acids from Your Diet

Your body, a complex machine, relies on a constant supply of amino acids—the building blocks of proteins—for countless vital processes. While it can manufacture many of these compounds, there are nine specific amino acids that it cannot synthesize on its own. These are known as essential amino acids (EAAs), and they are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They must be consistently provided by the food you eat to support protein synthesis, tissue repair, immune function, and more.

The Nine Essential Amino Acids and Their Roles

Each of the nine essential amino acids plays a unique and critical role in the body's functioning. A deficiency in any one of them can have significant health consequences, highlighting the importance of a balanced diet.

Histidine: Precursor to histamine, a neurotransmitter involved in immune response, digestion, and sexual function.
Isoleucine: A branched-chain amino acid (BCAA) that supports muscle metabolism and energy regulation.
Leucine: Another BCAA critical for protein synthesis and muscle repair.
Lysine: Essential for protein synthesis, hormone and enzyme production, and calcium absorption.
Methionine: Important for metabolism, detoxification, and tissue growth.
Phenylalanine: Needed for producing key neurotransmitters like dopamine, epinephrine, and norepinephrine.
Threonine: Crucial for structural proteins like collagen and elastin.
Tryptophan: A precursor for serotonin, which regulates mood, appetite, and sleep.
Valine: The third BCAA, involved in muscle growth, tissue regeneration, and energy production.

Complete vs. Incomplete Protein Sources

To get the nine essential amino acids, you need to consume proteins from various food sources. These sources are categorized based on their amino acid content.

Complete Proteins: These foods contain all nine essential amino acids in sufficient quantities. Animal-based products are the most common examples, though some plant-based options exist.
Incomplete Proteins: These foods lack one or more of the essential amino acids. Plant-based options like nuts, seeds, and most vegetables fall into this category. However, by combining different incomplete protein sources, you can ensure you get a complete profile of essential amino acids throughout the day.

Beyond the Essentials: Non-essential and Conditionally Essential

Of the 20 amino acids your body needs, the 11 it can produce are called non-essential amino acids. Under normal circumstances, you don't need to get these from your diet. However, certain amino acids are labeled conditionally essential, meaning that under specific conditions like illness, stress, or periods of rapid growth, your body's production cannot keep up with demand. In these cases, dietary intake or supplementation becomes necessary. Examples include arginine, glutamine, and tyrosine.

The Importance of a Varied Diet

For most healthy adults, consuming a balanced and varied diet is the easiest way to ensure an adequate intake of all amino acids. Animal protein sources, such as meat, fish, poultry, eggs, and dairy, are considered complete proteins. For those following a plant-based diet, combining different protein sources like legumes, nuts, seeds, and whole grains ensures all essential amino acids are consumed throughout the day. It is no longer necessary to combine specific plant proteins in a single meal to get all essential amino acids.


Feature	Essential Amino Acids (EAAs)	Non-Essential Amino Acids (NEAAs)	Conditionally Essential Amino Acids
Source	Must be obtained from diet	Synthesized by the body	Synthesized by the body, but needed from diet during specific conditions
Number	9	11	Subset of NEAAs (e.g., Arginine, Glutamine)
Dietary Requirement	Required daily	Not typically required daily	Needed during times of stress, illness, or rapid growth
Example Food Sources	Meat, eggs, dairy, soy, quinoa, buckwheat	Synthesized internally from other amino acids	May require supplementation during certain health crises

Conclusion

In total, nine amino acids are supplied by diet because the human body cannot produce them. The remaining 11 can be synthesized internally. A balanced diet featuring a variety of protein sources, both complete and incomplete, is the most effective way to ensure you meet all your essential amino acid needs. Understanding the distinction between essential, non-essential, and conditionally essential amino acids can help you make informed dietary choices to support your overall health and bodily functions. For specialized dietary guidance, especially during periods of high physiological demand, consulting with a healthcare professional or registered dietitian is recommended.

For more detailed information on protein and amino acid requirements, refer to the World Health Organization's guidelines.

World Health Organization guidelines on protein and amino acid requirements

Frequently Asked Questions

The human body requires 20 different amino acids to function correctly. These are used as building blocks for proteins, which are essential for many bodily processes.

A deficiency in essential amino acids can lead to decreased immunity, slowed growth, fatigue, and issues with digestive and neurological function, as your body cannot synthesize the proteins it needs.

No, a well-planned plant-based diet is not lacking in amino acids. While many plant proteins are incomplete, eating a variety of different plant protein sources throughout the day, such as beans, nuts, seeds, and grains, provides all nine essential amino acids.

For most healthy individuals eating a balanced diet, it is not necessary to track individual amino acid intake. The key is to consume a varied diet with a good mix of protein sources over the course of the day.

Excellent sources of complete proteins include animal products like meat, eggs, and dairy, as well as plant-based options such as soy, quinoa, and buckwheat.

Non-essential amino acids become conditionally essential during periods of physiological stress, such as illness, injury, or rapid growth. During these times, the body's demand for these amino acids can exceed its ability to produce them.

For most people, a healthy diet provides all the amino acids needed, making supplements unnecessary. While supplements can be beneficial in specific scenarios, they do not replace the need for a balanced, protein-rich diet.