fatten up vs alter

fatten up and alter both are verbs.

Word	Noun	Adjective	Verb	Adverb
fatten up	No	No	Yes	No
alter	No	No	Yes	No

As verbs, alter is a hypernym of fatten up; that is, alter is a word with a broader meaning than fatten up:

Other hypernyms of fatten up include change, modify.

fatten up (verb)	alter (verb)
make fat or plump	remove the ovaries of
	become different in some particular way, without permanently losing one's or its former characteristics or essence
	cause to change; make different; cause a transformation
	insert words into texts, often falsifying it thereby
	make an alteration to