California guys perhaps tucking into healthy fibre (8)
I believe the answer is:
filament
'fibre' is the definition.
(I know that filament is a type of fibre)
'california guys perhaps tucking into healthy' is the wordplay.
'california guys perhaps' becomes 'LA men' (men from Los Angeles in California).
'tucking into' is an insertion indicator.
'healthy' becomes 'fit' (synonyms).
'lamen' placed inside 'fit' is 'FILAMENT'.
(Other definitions for filament that I've seen before include "'Thin wire, in a bulb say (8)'" , "Strand" , "Wire in incandescent bulb" , "One may be incandescent" , "Wire in light bulb" .)