Those people ignoring hotel, knowing about high-protein food (6)
I believe the answer is:
tempeh
'high-protein food' is the definition.
(dish made from soy beans)
'those people ignoring hotel knowing about' is the wordplay.
'those people' becomes 'them' (I've seen this before).
'ignoring' suggests deleting specific letters.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'knowing' becomes 'hep' (alternative to 'hip', which can mean informed).
'about' says the letters should be written backwards.
'them' with 'h' removed is 'tem'.
'hep' written backwards gives 'peh'.
'tem'+'peh'='TEMPEH'
(Another definition for tempeh that I've seen is " Indonesian soya dish; meet HP (anag.)".)