Dietary fibre (8)
I believe the answer is:
roughage
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dietary fibre</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for roughage that I've seen before include "Essential food" , "Bulk" , "Indigestible material to stimulate intenstines" , "Indigestible material good for intestines" , "Vegetable fibre" .)