Exploring What Amino Acids Do Egg Yolks Have for Complete Nutrition

November 11, 2025 •

3 min read

With egg protein recognized as a highly digestible and excellent source of essential amino acids, boasting a protein digestibility-corrected amino acid score (PDCAAS) of 100, it's worth exploring the specifics. Many wonder, what amino acids do egg yolks have, and how do they contribute to the egg's exceptional nutritional value?

Quick Summary

Egg yolks provide a complete amino acid profile, including all essential types, making them a high-quality protein source. These amino acids are vital for muscle building, tissue repair, and hormone production, contributing significantly to overall health.

Key Points

Complete Protein Source: Egg yolks contain all nine essential amino acids, making them a complete protein.
Rich Nutritional Profile: The protein concentration in yolks is higher per gram than in egg whites, along with crucial vitamins and minerals.
Supports Muscle Health: Amino acids in the yolk, particularly BCAAs, are highly effective for muscle protein synthesis and repair.
Provides Antioxidant Action: The amino acid cysteine in yolks contributes to powerful antioxidant activity in the body.
Essential for Brain Function: The presence of choline and specific amino acid precursors in yolks supports cognitive health and brain development.
Consuming the Whole Egg: Eating the yolk with the white provides a more comprehensive nutritional boost than consuming egg whites alone.

The Complete Amino Acid Profile of Egg Yolks

Egg yolks are a concentrated source of high-quality protein, containing all nine essential amino acids that the human body cannot produce on its own and must obtain from food. Research indicates that egg yolks contain at least 19 different amino acids, making them a complete protein source with a superior nutritional package.

Essential Amino Acids in Egg Yolks

Egg yolks provide all nine essential amino acids:

Histidine: Important for tissue repair.
Isoleucine: A branched-chain amino acid (BCAA) critical for muscle metabolism.
Leucine: Another BCAA vital for muscle protein synthesis.
Lysine: Helps with calcium absorption.
Methionine: Involved in metabolism.
Phenylalanine: A precursor for tyrosine and other brain chemicals.
Threonine: Crucial for forming structural proteins like collagen.
Tryptophan: Used to produce serotonin.
Valine: The final BCAA, important for muscle growth and energy.

Non-Essential and Conditionally Essential Amino Acids

Beyond the essential types, egg yolks also contain non-essential amino acids, such as glutamic acid (involved in brain function), aspartic acid (plays a role in hormone production), and cysteine (a sulfur-containing antioxidant). Proline, important for skin health, and serine are also present.

Yolk vs. White: A Protein Comparison

Egg yolks provide a more concentrated protein dose per gram compared to egg whites and offer a richer nutrient profile. Nearly half of an egg's protein is located in the yolk. Consuming the whole egg unlocks its full nutritional benefits.


Nutrient Aspect	Egg Yolk	Egg White
Protein Content (per 100g)	15.86g	10.9g
Essential Amino Acids	All nine, in a concentrated profile	All nine, less concentrated
Vitamins	Contains fat-soluble (A, D, E, K), B vitamins, and choline	Trace B vitamins only
Minerals	Rich in iron, zinc, selenium, and phosphorus	Lower concentrations
Fats	Rich in healthy fats, including omega-3s, and lecithin	Fat-free

The Functional Benefits of Yolk Amino Acids

The amino acids in egg yolks offer specific health benefits:

Antioxidant Action: Cysteine in yolks contributes to glutathione synthesis, a potent antioxidant. Phenylalanine and tyrosine also act as antioxidants.
Cognitive and Brain Health: Yolks are a source of choline, vital for brain function and development, which relies on certain amino acids for synthesis.
Muscle Support: The high content of BCAAs (leucine, isoleucine, valine) and other essential amino acids in yolks effectively supports muscle repair and growth after exercise. Whole egg consumption can promote greater muscle protein synthesis than egg whites alone.
Immune System Enhancement: Certain amino acid chains (peptides) in egg yolks have demonstrated antimicrobial and immunomodulatory effects.

Conclusion: More Than Just Protein

Understanding what amino acids do egg yolks have highlights their significance as a highly digestible, complete protein source rich in all essential amino acids, alongside non-essential types. This amino acid profile, combined with essential vitamins, minerals, and healthy fats, makes the whole egg a superior nutritional choice. The amino acids in the yolk play crucial roles in muscle support, brain health, antioxidant defense, and overall wellness. For those seeking comprehensive dietary protein and health benefits, consuming the entire egg is highly recommended.

For additional information on egg protein, refer to the National Institutes of Health. More on the health benefits of egg protein.

Frequently Asked Questions

Yes, while both contain all essential amino acids, the protein concentration is higher in the yolk per gram. The yolk also contains unique, functional amino acids and bioactive peptides that differ from those in the white.

Yes, egg yolks are a complete protein source because they contain all nine of the essential amino acids that the human body cannot synthesize on its own.

Cooking primarily affects the protein structure, making it more digestible. While heat can impact some bioactive properties, the amino acid profile itself remains largely intact. Some studies suggest benefits from both heated and unheated egg proteins.

Egg yolks contain a high concentration of branched-chain amino acids (BCAAs), such as leucine, which is critical for stimulating muscle protein synthesis and promoting muscle repair after exercise.

Beyond muscle building, the amino acids in egg yolks support a healthy immune system, provide antioxidant protection against oxidative stress (via cysteine), and contribute to overall tissue repair and health.

Eggs as a whole are often considered the gold standard for protein quality due to their high bioavailability and complete amino acid profile. Some studies suggest eggs have the best amino acid profile compared to many other sources like meat, milk, and soy.

For maximum benefit, you should eat the whole egg. While the egg white is high in protein, the yolk provides a greater concentration of protein per gram and is where almost all the other vital nutrients, vitamins, and minerals are found.