"Jerry calls the simple NPN compounds "funny protein" to distinguish them from "true protein" amino acids--complex nitrogen and mineral compounds essential for normal digestion, reproductive function, cell repair, and a strong immune system."
3) Blood Urea Nitrogen (B.U.N.) also tested as Milk Urea Nitrogen (M.U.N.) suggests that either too much protein or typically too much “funny protein” which is non-protein nitrogen (NPN) is being consumed.
“Protein- It Ain’t Just Nitrogen- Part 1: True Protein vs ‘Funny Protein’” Part 1 (Acres U.S.A. February 2004)
"Specifically preferred is an alternating process wherein the first and second ionic feed solutions comprise nitrogen isotopes in alkaline state and sulfur isotopes in acidic state, respectively."
these are just a few things I dug up for you and the readers... there are many more.