German watching his weight? (6)

I believe the answer is:

dieter

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'german' is the definition.
(common German name)

I cannot understand how the rest of the clue works.

(Other definitions for dieter that I've seen before include "one trying to lose weight" , "One watching one's weight" , "fellow who'll eat less?" , "bloke obeying regime" , "person who's determined to lose" .)

I've seen this clue in The Sun.

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