Merge the rings of slow digestion and regeneration. Keep the name “regeneration”; make it chargeable. A positive rate boots your regeneration and your hunger rate, up until they are doubled at +10; a negative rate decreases both until they are halved at -10, with the intermediate values scaling as appropriate.

Possibly, since the extremes of &177;10 are hard to attain, make the doubling/halving threshold at &177;7 instead.