Leaders to advocate celery as indispensible superfood (4)
I believe the answer is:
acai
'superfood' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'leaders to advocate celery as indispensible' is the wordplay.
'leaders to' indicates taking the first letters (I've seen 'leader to' mean this (the letter which leads the word)).
The first letters of 'advocate celery as indispensible' is 'ACAI'.
Can you help me to learn more?
(Other definitions for acai that I've seen before include "South American palm tree" , "something nutritional to eat" , "South American food product" , "fruit which is nutritious" .)