Concept:
Dietary fibre is the indigestible part of plant food.
Step 1: Fibre increases bulk in stool.
Step 2: It helps bowel movement.
Step 3: This prevents constipation and supports gut health.
Step 4: Fibre does not increase calorific value significantly.
\[
\boxed{\text{Preventing constipation and improving gut health}}
\]