L-lysine is an essential amino acid that the body cannot produce on its own, making it necessary to obtain from food sources. It plays a role in the production of collagen, antibodies, and enzymes, and is also important for energy metabolism and nerve function. L-lysine is found in high concentrations in animal proteins such as meat, poultry, fish, eggs, and dairy products. It can also be obtained from plant sources such as legumes, nuts, and seeds.