What you have is the "Gesund durch Vollkornbrot" commemorative cancel.

It's listed in the Generalgouvernement Study Group's
Documentation on the Publicity Cancels in the Deutsche Post Osten in the Generalgouvernement, Handbook #H67 E as Cancel W5.
There were two varieties. One had a period in the circle (W5a), and the other had a cross (W5b). Yours appears to be a W5b.

The text roughly translates as "Healthy through whole-grain bread -- introduced and recommended by the Arbeitsbereich Generalgouvernement". The Arbeitsbereich Generalgouvernement was formed by the Nazi Party (NSDAP) to centralize all the various Nazi-related groups operating within the Generalgouvernement under one umbrella so they might be more closely controlled politically, ideologically, etc. Part of its efforts included making "recommendations" such as this.
These were in use from:
5a: 30 Oct 41 - 1 Jan 45
5b: 30 Oct 41 - 16 Nov 43
Here's what it looks like complete, on cover.
