Good health shown by a professional model (6)
I believe the answer is:
prosit
'good health' is the definition.
(German toast for drinking someone's health)
'by a professional model' is the wordplay.
'by' says to put letters next to each other.
'a professional' becomes 'pro' (abbreviation).
'model' becomes 'sit' (e.g. for a painting).
'pro'+'sit' is 'PROSIT'.
'shown' acts as a link.
(Other definitions for prosit that I've seen before include "I sport with a drinking toast in Germany" , "Drinking salutation" , "Happy days, perhaps" , "Bottoms up (in Germany)" , "... [good-health]" .)