Ruin tent, cooking a bit of food (8)
I believe the answer is:
nutrient
'a bit of food' is the definition.
'nutrient' can be an answer for 'food' (synonyms). I am not sure about the 'a bit of' bit.
'ruin tent cooking' is the wordplay.
'cooking' indicates anagramming the letters (cook can mean to falsify or distort).
'ruin'+'tent'='ruintent'
'ruintent' anagrammed gives 'NUTRIENT'.
Can you help me to learn more?
(Other definitions for nutrient that I've seen before include "Substance essential for growth" , "Nourishing substance" , "Something providing nourishment" , "Good food" , "A food that keeps one alive and healthy" .)