So I think what you can do is when you are hungry, you can cram poisonous potatoes into your mouth, and then you can restore more hunger bars than a normal potato.
Interestingly, a poisonous potato actually restores more hunger and gives more saturation than a normal, unpoisoned potato.
To counteract the effects of the poison, you can drink some milk when
you've done eating the poisonous potatoes- it doesn't have any
nutritional value, but will cancel the poisonous effects.
(Neil Slater, via a comment moved to this answer)