Green’s Dictionary of Slang

(N.Z. prison) the No. 1 restricted (i.e. punishment) diet .

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 130/2: one-one diet (also 1 1 Diet) n. a punishment diet formerly handed out to inmates that involved one day of the Restricted Diet Number One followed by one day of the Standard Ration.