L-lysine is an amino acid found in natural proteins of animal and plant origin. It belongs to the group of essential amino acids that must be supplemented through diet or supplements.

Essential amino acids, such as L-lysine, are amino acids that are not sufficiently present in the organism itself and therefore must be supplied through external sources. Non-essential amino acids can in many cases be built from other nutrients that are present.

L-lysine is especially present in protein-rich products of animal origin, such as meat, fish, poultry, eggs, and dairy. Among plant sources, legumes, quinoa, and soy products are among the richer suppliers, although these generally contain smaller amounts.