Understanding the Essential Amino Acids: 8 or 9?

Proteins, the building blocks of life, are composed of amino acids. Out of the many amino acids our bodies need, only some must be obtained from food; these are called essential amino acids. The number of these essential amino acids can be a point of debate in the field of protein science. Let's delved into the details.

Introduction to Essential Amino Acids

Essential amino acids are those amino acids that the body cannot synthesize on its own. They must be obtained through the diet. As the name implies, these are essential for proper growth and maintenance of the body.

Current Expert Consensus

According to the majority of protein science experts, the total number of essential amino acids we need from food is 9. These are:

Isoleucine Lysine Leucine Methionine Phenylalanine Threonine Tryptophan Vafilecine Histidine

However, this number of 9 has been under scrutiny as some experts argue that histidine should be considered only "conditionally essential," especially for adults.

The Controversy: 8 or 9 Essential Amino Acids?

The debate over the number of essential amino acids is centered around the classification of histidine. Histidine is a key amino acid that plays important roles in the body, including the production of dopamine, histamine, and melanin. It is pivotal in the growth and repair of cells and in the formation of myelin sheaths around nerve fibers.

Historically, it was believed that histidine was not "essential" for adults because the body could synthesize it. However, recent research has suggested that this is not always the case, especially in certain conditions of illness or under certain dietary restrictions. Some experts now consider histidine as the ninth essential amino acid, bringing the total to a widely accepted 9 essential amino acids.

Conditional Versus Essential

When we say that histidine is "conditionally essential," it means that the body cannot produce enough of it under certain conditions. For example, in the case of newborns and in some rare genetic disorders, the body may not be able to synthesize histidine efficiently. In such cases, histidine becomes an essential amino acid and must be obtained through the diet.

Conclusion

The number of essential amino acids is a topic of ongoing debate, reflecting the dynamic and evolving nature of scientific research. While the current consensus is that 9 essential amino acids are necessary, the status of histidine is still a matter of discussion. It is important to consult with a healthcare provider or a nutritionist to ensure you are meeting all your dietary needs, especially if you have specific health conditions or dietary restrictions.

Further Reading and Resources

Citing from reliable sources, such as The Essentials - Part One - UC Davis Integrative Medicine, further reading and detailed explanations of amino acids and their importance are available. These resources are great for those who want to dive deeper into the science behind essential amino acids.