"Lose weight where applicable."
Translation:Nehmen Sie gegebenenfalls ab.
can someone explain how a non-German speaker unfamiliar with idiomatic usage is supposed to understand how anything in this sentence would lead one to the phrase "to lose weight?"
abnehmen = to lose weight
It's not actually an idiom. You're probably confused by the separable prefix.
By the way, the English translation seems a bit odd. I'd translate it as "Lose weight if necessary".
I agree, "Lose weight if necessary" is the better translation. As for the English "where applicable" I would never use it refering to a person.