If you look at the package for lean ground beef...4oz contains maybe 20 grams protein
1 ounce = 28.3495231 grams
28.35 x 4 =113.4 grams
so 20/113.4 means that about 17% of lean ground beef is protein. The rest...fat and water.
Mix that with some veggie matter and you're probably down to about 10% also