food for thought vs food

food for thought and food both are nouns.

Word	Noun	Adjective	Verb	Adverb
food for thought	Yes	No	No	No
food	Yes	No	No	No

As nouns, food for thought and food are synonyms defined as:

food for thought and food: anything that provides mental stimulus for thinking

Other synonyms of food for thought include intellectual nourishment.

food for thought (noun)	food (noun)
anything that provides mental stimulus for thinking	any substance that can be metabolized by an animal to give energy and build tissue
	anything that provides mental stimulus for thinking
	any solid substance (as opposed to liquid) that is used as a source of nourishment