Type of diet perhaps in forefront (5)
I believe the answer is:
vegan
'type of diet' is the definition.
(veganism is a special diet)
'perhaps in forefront' is the wordplay.
'perhaps' becomes 'eg' (for example).
'in' means one lot of letters goes inside another.
'forefront' becomes 'van' (van can mean the front part of something).
'eg' inserted within 'van' is 'VEGAN'.
(Other definitions for vegan that I've seen before include "Non-consumer of animal products" , "One not eating animals" , "One shunning animal products" , "One avoiding all animal-based food" , "One not eating or using animal products" .)