What is L-Lysine? L-Lysine is an essential amino acid; which means it cannot be synthesised by the body & must be consumed in the diet. For this reason it is often recommended to supplement with Lysine to ensure that you are obtaining sufficient amounts. Lysine can be found in foods such as beans, cheese, yoghurt, milk, brewer’s yeast & meat, However, obtaining the optimal amount through food can be challenging. The Lysine content of foods is also often reduced through preparation