L-lysine is an essential amino acid that occurs naturally as part of food proteins and cannot be manufactured by the body. It is usually the limiting factor in the biological availability of vegetable proteins and this means that vegetarians (and especially vegans) have to plan their diets carefully in order not to suffer from a deficiency of L-lysine. Lysine is one of numerous amino acids that the body needs for growth and tissue repair. It is classified as one of the nine "essential" amino acids because you need to get it from outside sources such as foods or supplements--in other words the body can't make it on its own.

L-lysine is an important structural component of many proteins. It is also directly involved in the production of L-carnitine, which is required for the transport, and utilisation of fats. Lysine is needed to make the non-essential amino acid, carnitine, involved in fat transportation. Two other roles in which L-lysine is involved are retention of Calcium within the body and maintenance of the immune system. Lysine is an amino acid that is a building block for all protein. In children it is essential for skeletal (bone) development, and helps all ages to absorb calcium. Lysine also benefits the production of enzymes, hormones, antibodies, and collagen. When vitamin C is combined with lysine, the formation of collagen is enhanced. Collagen is important to the formation of bone and tissue along with its repair. Lysine is not produced by the body and therefore must be absorbed from food intake and/or supplements.

Because lysine helps to build muscle protein, it is good for those recovering from surgery and sports injuries. It also lowers high serum triglyceride levels. Another useful property of this amino acid is its capacity for fighting cold sores and herpes viruses. Taking supplemental L-lysine, together with vitamin C with bioflavonoids, can effectively fight and/or prevent herpes outbreaks.

L-Lysine enhances the assimilation and absorption of calcium, and it ensures the formation of cartilage, bone, connective tissues and collagen. L-Lysine is not produced by the body and must be obtained via the diet. Some natural food sources for L-Lysine include lima beans, kidney beans, potatoes, corn, red meat, fish and milk. L-Lysine is necessary for helping the immune system produce antibodies that are necessary for warding off viral infections, making it beneficial for treating herpes, cold sores, mouth ulcers, and fevers. L-Lysine is also beneficial for regulating glands, controlling acid/alkaline balance and assisting with the assimilation of all amino acids.

L-Lysine deficiencies may include fatigue, moodiness, anemia, poor concentration, reproductive problems and slow development. L-Lysine supplementation helps maintain the health of the structural, circulatory and immune systems.
There are many food sources for lysine including cheese (Parmesan), fish (dried and salted cod), milk, potatoes, torula yeast, red meat, and many soy-based products such as tofu, low-fat soybean flour, and soybean protein concentrate. The soy-based products are especially beneficial to vegetarians, who may find it difficult to enrich their diets with lysine. Lysine is also available as L-lysine acetylsalicylate (LAS), Lysine clonixinate (LC), and L-lysine monohydrochlorine (LMH).