The protein scoring methodologies ( https://en.wikipedia.org/wiki/Protein_Digestibility_Corrected_Amino_Acid_Score) rate plant proteins of a lower quality than animal proteins. Now I can understand the reasoning that proteins have a lesser quantity of essential amino acids (allegedly) making them "lower quality" in terms of protein; but I don't see why there should be a difference in digestibility between plant and animal proteins (I can give links but it's common knowledge that plant proteins are less digestible). What is the basis for this difference in digestibility ? Whatever the amino acid composition, I don't see how that would affect digestion of proteins. So why are plant proteins considered less digestible ?