dietetics vs bioscience

dietetics and bioscience both are nouns.

Word	Noun	Adjective	Verb	Adverb
dietetics	Yes	No	No	No
bioscience	Yes	No	No	No

As nouns, bioscience is a hypernym of dietetics; that is, bioscience is a word with a broader meaning than dietetics:

dietetics: the scientific study of food preparation and intake
bioscience: any of the branches of natural science dealing with the structure and behavior of living organisms

Other hypernyms of dietetics include life science.

dietetics (noun)	bioscience (noun)
the scientific study of food preparation and intake	any of the branches of natural science dealing with the structure and behavior of living organisms