fast food vs alimentation

fast food and alimentation both are nouns.

Word	Noun	Adjective	Verb	Adverb
fast food	Yes	No	No	No
alimentation	Yes	No	No	No

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

fast food: inexpensive food (hamburgers or chicken or milkshakes) prepared and served quickly
alimentation: a source of materials to nourish the body

Other hypernyms of fast food include aliment, nourishment, nutriment, nutrition, sustenance, victuals.

fast food (noun)	alimentation (noun)
inexpensive food (hamburgers or chicken or milkshakes) prepared and served quickly	the act of supplying food and nourishment
	a source of materials to nourish the body