He perhaps is prudent to lose weight being simple (10)
I believe the answer is:
elementary
'being simple' is the definition.
(synonyms)
'he perhaps is prudent' is the wordplay.
'he perhaps' becomes 'element' (helium - symbol 'He' - is an example).
'is prudent' becomes 'ary' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'element'+'ary'='ELEMENTARY'
'to lose weight' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for elementary that I've seen before include "No problem" , "Fundamental" , "One precursor to 7 [SECONDARY MODERN]" , "Rudimentary; introductory" , "schooling?" .)