Source of dietary fiber (4)
I believe the answer is:
bran
'source of dietary fiber' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bran that I've seen before include "Husks of cereal seeds sifted from flour" , "Horse food stored in barn" , "Husks of cereal grain" , "Milled grain husk" , "Healthy breakfast" .)