low-salt diet vs salt-free diet

low-salt diet and salt-free diet both are nouns.

Word	Noun	Adjective	Verb	Adverb
low-salt diet	Yes	No	No	No
salt-free diet	Yes	No	No	No

As nouns, low-salt diet and salt-free diet are synonyms defined as:

low-salt diet and salt-free diet: a diet that limits the intake of salt (sodium chloride); often used in treating hypertension or edema or certain other disorders

Other synonyms of low-salt diet include low-sodium diet.

low-salt diet (noun)	salt-free diet (noun)
a diet that limits the intake of salt (sodium chloride); often used in treating hypertension or edema or certain other disorders	a diet that limits the intake of salt (sodium chloride); often used in treating hypertension or edema or certain other disorders