About 500 amino acids are found in nature. Twenty of these are amino acids that serve as building blocks for proteins in the human body, these are referred to as 'fundamental amino acids'. These fundamental amino acids can again be subdivided into the categories 'essential', 'semi-essential' and 'non-essential'. L-lysine belongs to the so-called essential amino acids, which means that the body cannot make it itself from other amino acids, and that one is completely dependent on food to meet the daily requirement. In vegetarians and vegans, the intake of lysine may be insufficient, since animal proteins in particular are rich in lysine.