Outlaw eating right source of dietary fibre (4)
I believe the answer is:
bran
'dietary fibre' is the definition.
'bran' can be an answer for 'fibre' (I've seen this before). I am unsure of the 'dietary' bit.
'outlaw eating right source' is the wordplay.
'outlaw' becomes 'ban' (banning is a kind of outlawing).
'eating' is an insertion indicator.
'source' says to take the initial letters (source can mean a beginning or origin).
The first letter of 'right' is 'r'.
'ban' enclosing 'r' is 'BRAN'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for bran that I've seen before include "Refuse providing fibre" , "Outer covering of grain" , "Food from the husks of cereal grains" , "Food for horses in barn" , "Milled grain husk" .)