How do I solve 2 down in Daily Telegraph Cryptic 31245?

Question

Accepted Answer

2 down reads "Invalid fed soup or something nutritious" (9 letters); the answer is SUPERFOOD. It's an anagram clue: the answer is a rearrangement of letters supplied by the clue itself. Look for an indicator like 'mixed', 'broken', 'cooked', or 'wild', and find a phrase whose letters add up to the answer's length. The full step-by-step breakdown is on this page.

Invalid fed soup or something nutritious (9)

2D — Invalid fed soup or something nutritious (9) — SUPERFOOD