That's because its surface protein haemagglutinin doesn't contain many short amino acid sequences — called epitopes — that trigger helper T - cells in the body to stimulate antibody - making cells.
Other problem areas include: phytates, which block the body's uptake of minerals; enzyme inhibitors, which hinder protein digestion; and haemagglutinin, which causes red blood cells to clump together and inhibits oxygen take - up and growth.