Fruit, low in calories, added to compost (8)

'compost' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'fruit low in calories added' is the wordplay.
'fruit' becomes 'pear' (pear is a kind of fruit).
'low in calories' becomes 'lite' (light in calories, calorie-lite).
'added' is a charade indicator (letters next to each other).
'pear'+'lite'='PEARLITE'

'to' is the link.

Can you help me to learn more?