breakfast food vs food

breakfast food and food both are nouns.

Word	Noun	Adjective	Verb	Adverb
breakfast food	Yes	No	No	No
food	Yes	No	No	No

As nouns, food is a hypernym of breakfast food; that is, food is a word with a broader meaning than breakfast food:

breakfast food: any food (especially cereal) usually served for breakfast
food: any solid substance (as opposed to liquid) that is used as a source of nourishment

Other hypernyms of breakfast food include solid food.

breakfast food (noun)	food (noun)
any food (especially cereal) usually served for breakfast	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