They were measuring nitrogen, not protein. My bad, sorry about that. The studies were done on people who were
weight training. Unfortunately, that is an depth as they gave the results. They also did not mention which journal the study was from, or where it originated. The book was written for the general public, not academia which explains the lack of citing references.
Will have to postpone discussing this further for now. Gotta leave for the weekend. Looking forward to resuming when I get back. Have a great weekend everyone.