to be off ones food

from The Collaborative International Dictionary of English v.0.48

Off \Off\, prep.
   Not on; away from; as, to be off one's legs or off the bed;
   two miles off the shore. --Addison.
   [1913 Webster]

   {Off hand}. See {Offhand}.

   {Off side}
   (Football), out of play; -- said when a player has got in
              front of the ball in a scrimmage, or when the ball
              has been last touched by one of his own side
              behind him.

   {To be off color},
   (a) to be of a wrong color.
   (b) to be mildly obscene.

   {To be off one's food} or {To be off one's feed}, (Colloq.)
      to have no appetite; to be eating less than usual.
      [1913 Webster]