I've no idea what mcd.s does, but you can add all sorts of crap to hamburger before it becomes too obvious. Probably a lot of it is not ... so appetizing (the bits you don't want to know you're eating, etc).

My mom used to buy hamburger meat that was bulked up with soy protein, mainly because it was cheaper than pure ground meat. [I absolutely loved the taste of that stuff actually, much more than all-meat burgers! Wish I could find it as an adult...]