bland diet vs diet

bland diet and diet both are nouns.

Word	Noun	Adjective	Verb	Adverb
bland diet	Yes	No	No	No
diet	Yes	No	Yes	No

As nouns, diet is a hypernym of bland diet; that is, diet is a word with a broader meaning than bland diet:

bland diet (noun)	diet (noun)
a diet of foods that are not irritating	the act of restricting your food intake (or your intake of particular foods)
	a prescribed selection of foods
	the usual food and drink consumed by an organism (person or animal)
	a legislative assembly in certain countries (e.g., Japan)

bland diet (verb)	diet (verb)
	eat sparingly, for health reasons or to lose weight
	follow a regimen or a diet, as for health reasons