Lysine is one of nine essential amino acids. This indispensable amino acid is required for protein synthesis, collagen development, proper cell function, and tissue repair. But your body cannot make it on its own. You have to get it from the foods you eat or the supplements you take. Lysine supplementation, however, comes with its own set of best practices.
In developed countries, such as the United States, lysine is an abundant nutrient in the majority of people’s diets. However, in poor countries where cereals are relied upon heavily as “nutrition,” lysine is the most limiting amino acid. The phrase “most limiting” means that out of the nine essential amino acids in protein food sources, lysine is the most deficient. In other words, the amount of lysine in the food supply of less developed countries does not meet dietary lysine requirements, making lysine the most limiting amino acid and affecting the body’s ability to build new protein.
Based on animal studies, every cereal grain that has been studied contains an insufficient amount of lysine. Lysine is also the most limiting amino acid in pig feed, and falls just behind methionine as the second most limiting amino acid in avian diets. Over 90% of lysine produced is used to supplement animal diets. In 2005, 200,000 metric tons of lysine were used in the United States alone to supplement animal feed. I bring this up merely to make the point that lysine is most likely the most studied amino acid in animal nutrition, but has received far less attention for its role in human nutrition. Still, let’s explore what we know thus far.
What Are the Symptoms of Lysine Deficiency?
A lysine deficiency is characterized by broken skin, fragile nails, and in extreme cases hair loss. If you are deficient in lysine you may also notice that your appetite has decreased, which can lead to subsequent weight loss. Other symptoms of lysine deficiency include extreme fatigue and unexplained mood changes.
While lysine is supplied by many animal proteins (red meats, fish, and dairy products), it is typically the limiting amino acid in plant proteins. Vegetarians, especially vegans, must be diligent in choosing proteins or taking an essential amino acid supplement to ensure adequate lysine intake.
Lysine and Muscle Protein
Lysine is an important component of muscle protein. In fact, it is the second most abundant essential amino acid in human muscle protein. Even so, lysine does not play a significant role in molecular signaling and protein synthesis and is only effective in stimulating the synthesis of new muscle protein when it is included in a mixture of all the essential amino acids.
Muscle protein is comprised of 20 different amino acids, and 9 of these are essential amino acids. In order to build new muscle protein, each of these amino acids must be available in the muscle cell roughly in proportion to their contribution to the profile of amino acids in muscle protein. Lysine, however, is a bit of an outlier.
For maximal effectiveness in stimulating muscle protein synthesis, an essential amino acid formulation must contain more lysine than the amount of lysine found in muscle protein. This is because some dietary lysine may be altered during digestion, rendering it useless. Also, once lysine is in the blood, it is transported into muscle very sluggishly. Therefore, you need to consume more lysine to achieve the optimal balance of essential amino acids inside the muscle cells.
Lysine and the Immune System
In addition to its important role as a component of muscle protein, lysine is a key player in the immune system. Lysine is involved in the development of antibodies and has important antiviral properties.
As a nutritional supplement, lysine is promoted to be active against certain viruses, including herpes simplex viruses. It can be taken by mouth or applied topically to cold sores.
The important role of lysine and immunity to infections is particularly evident when the diet is deficient in lysine. A diet deficient in lysine impairs immune function and increases the susceptibility of animals and humans to infectious disease. A diet uniquely deficient in lysine will, therefore, benefit from lysine supplementation. This is most common in the case of a vegan diet.
A diet more generally deficient in protein or amino acids will also impair immune function. In this case, care must be taken when you are supplementing with an individual amino acid, including lysine, to support immune function.
There is an integrative relationship between the various amino acids involved in immune function. Arginine, glutamine, and cysteine are considered the most crucial amino acids for proper immune function, and lysine competes for transport with these amino acids. Therefore, an excess of lysine relative to other key amino acids may actually impair immune function. Maintaining a normal balance of amino acids in the blood is therefore crucial for optimal immune system function.
Lysine and the Maillard Reaction
The Maillard reaction is a chemical reaction between amino acids and sugars that gives browned food its complex flavor (think: dark coffee, toasted bread, and charred meat). Most protein sources for human nutrition that have been processed in a factory are heat treated, which facilitates the formation of Maillard reactions. These reactions are accelerated at higher temperatures.
Lysine is particularly susceptible to Maillard reactions because it possesses a reactive amino group at the end of its side group. Maillard products can make lysine nutritionally unavailable. Free lysine, either alone or in a balanced essential amino acid formulation, is not subject to Maillard reactions.
Additional Benefits of Lysine Supplementation
A variety of other benefits of lysine have been claimed, including as a natural treatment for cancer and diabetes, as well as a curative for anxiety and other psychological problems. These varied benefits have yet to receive wide acceptance due to the lack of controlled clinical trials documenting these claimed benefits.
So, I’d like to leave you with this: Individual lysine supplementation is appropriate for diets specifically deficient in lysine, such as animal feed. For most circumstances, a more balanced formulation of essential amino acids is appropriate, with the understanding that lysine should comprise at least 20% of the essential amino acids to account for incomplete digestion as well as slow transport into muscle cells.