food vs food for thought

food and food for thought both are nouns.

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

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

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

Other synonyms of food include intellectual nourishment.

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