What Are 1st Class Proteins? The Complete Guide to Essential Nutrients

December 25, 2025 •

3 min read

Over 90% of the proteins in the human body are made up of 20 amino acids. Understanding what are 1st class proteins is crucial, as they contain all the essential amino acids your body cannot produce on its own, making them a cornerstone of a healthy and balanced diet.

Quick Summary

First class proteins are complete proteins containing all nine essential amino acids required by the human body for growth, repair, and vital functions. They are primarily found in animal-based foods, though some plant sources also qualify.

Key Points

Complete Amino Acid Profile: 1st class proteins, also known as complete proteins, contain all nine essential amino acids that the human body cannot produce on its own.
Sources: First class proteins are found in animal products like meat, eggs, and dairy, as well as in certain plant-based foods such as soy, quinoa, and hemp seeds.
Body Functions: These proteins are crucial for numerous bodily processes, including muscle growth, tissue repair, hormone production, and immune system function.
Incomplete Proteins: Many plant-based proteins are "second class" or incomplete, lacking one or more essential amino acids, but can be combined to form a complete profile.
Dietary Importance: Consuming a variety of 1st class protein sources or strategically combining incomplete ones is key to ensuring adequate intake for optimal health and bodily function.
High Biological Value: First class proteins have a high biological value, meaning the body can absorb and utilize their amino acids very efficiently.

The Building Blocks of a Healthy Body

To understand what are 1st class proteins, one must first appreciate the role of amino acids. Protein is a macronutrient composed of smaller organic compounds called amino acids. The human body needs 20 different amino acids to function properly. While 11 are non-essential and can be synthesized by the body, the remaining nine are essential and must be obtained from the diet.

A 1st class protein, also known as a complete protein, is a food source that provides all nine essential amino acids in sufficient amounts. These proteins are vital for repairing tissues, building muscle, producing enzymes and hormones, and supporting the immune system. A deficiency in essential amino acids can impair these functions and potentially lead to health issues like muscle wasting or weakened immunity.

Why Are Some Proteins Incomplete?

Unlike 1st class proteins, 2nd class or incomplete proteins lack one or more essential amino acids. Most plant-based proteins fall into this category. For instance, grains often lack lysine, and legumes may be low in methionine. However, by combining different incomplete protein sources, such as beans with rice, a complete amino acid profile can be achieved through complementary proteins.

Sources of First Class Proteins

First class proteins are commonly found in animal products, which naturally contain all essential amino acids. There are also several plant-based sources that qualify as complete proteins.

Animal-Based Sources

Meat (beef, chicken, pork, lamb)
Poultry (chicken, turkey)
Fish (salmon, tuna, cod)
Eggs
Dairy products (milk, cheese, yogurt, whey)

Plant-Based Sources

Soy products (edamame, tofu, tempeh)
Quinoa
Buckwheat
Hemp seeds and spirulina

First Class vs. Second Class Proteins: A Comparison

Here's a comparison highlighting the key differences between first and second class proteins:


Feature	First Class Proteins	Second Class Proteins
Amino Acid Profile	Contains all nine essential amino acids.	Lacks one or more essential amino acids.
Primary Sources	Animal products, soy, quinoa, buckwheat.	Most plant-based foods (legumes, nuts, grains).
Completeness	Considered "complete" on their own.	Considered "incomplete" individually.
Nutritional Synergy	The body can use the protein directly.	Requires combining sources for a complete profile.
Biological Value	Generally higher for efficient utilization.	Generally lower due to limiting amino acids.

The Importance of Protein Quality for Your Body

Protein quality, determined by amino acid composition, is crucial for efficient protein synthesis. First class proteins are valuable because their amino acid profile closely aligns with the body's needs.

Muscle Growth and Repair: Essential for athletes and strength training.
Tissue Maintenance: Needed for constant repair and maintenance of all tissues.
Hormone and Enzyme Production: Many hormones and all enzymes are proteins, requiring a full spectrum of amino acids.
Immune System Support: Antibodies are proteins synthesized from amino acids; deficiencies can impair immune function.
Weight Management: Protein promotes satiety, aiding appetite control and weight management.

Conclusion

Understanding what are 1st class proteins is essential for a healthy diet. These complete proteins, sourced from animals or specific plants like soy and quinoa, provide all essential amino acids in the right balance. While many plant proteins are incomplete, they can be combined to meet protein requirements in vegetarian or vegan diets. Prioritizing diverse, high-quality protein sources ensures your body has the necessary building blocks for optimal function, muscle support, tissue maintenance, and a strong immune system. For more information on protein functions, refer to resources such as Healthline.

Frequently Asked Questions

The main difference is their amino acid profile. First class proteins, or complete proteins, contain all nine essential amino acids, while second class proteins, or incomplete proteins, lack one or more of these essential amino acids.

Generally, yes. Animal-based sources such as meat, fish, eggs, and dairy are considered first class because they provide all the essential amino acids in the proportions needed by the human body.

Yes, vegans can get all the essential amino acids they need. While most plant proteins are incomplete, certain sources like soy, quinoa, and buckwheat are complete. Combining different incomplete plant protein sources throughout the day, such as rice and beans, also provides a complete amino acid profile.

Essential amino acids are critical because the human body cannot produce them. They must be obtained from the diet to support vital functions like building and repairing tissues, creating enzymes and hormones, and maintaining a healthy immune system.

No, it is a common myth that complementary proteins must be eaten together at the same meal. As long as you consume a variety of incomplete protein sources throughout the day, your body can create a complete amino acid profile from its amino acid pool.

Biological value (BV) is a measure of how efficiently the body can absorb and utilize a protein. First class proteins generally have a higher BV because their amino acid composition is well-suited for human physiological needs.

In most cases, proper cooking methods do not significantly degrade the quality of first class protein. High heat can denature protein, but it does not destroy the amino acids themselves. Overcooking can lead to some nutrient loss, but it won't render a complete protein incomplete.