German slimmer (6)
I believe the answer is:
dieter
I believe this is a double definition.
'german' is the first definition.
(I've seen this before)
'slimmer' is the second definition.
(I've seen this before)
(Other definitions for dieter that I've seen before include "One restricting food" , "One who's slimming" , "who wants to lose 13 [BULK]" , "The weight-watcher" , "who's getting slimmer?" .)