Why egg is consider the reference protein?

Eggs are considered the reference protein because they contain all nine essential amino acids in the right proportions needed by the human body. The protein in eggs, particularly the egg white, has a high biological value, meaning it is efficiently utilized for growth and maintenance of body tissues. Additionally, the digestibility of egg protein is very high, making it an ideal standard against which other protein sources are measured. This quality makes eggs a benchmark for evaluating the protein content of other foods.