Setting gamerule of natural regeneration to false does not work and natural regen problems

So I tried to test the regen effect of god apples, and so I set gamerule of natural regeneration to false and set my gamemode to survival and jump off a 20 block high cliff. WHen I land I take fall damage but then my health starts to regenerate. ANd I checked chat and gamerule was set to false so I apply hunger level 30 on myself and run around like crazy(sprint jumping) ANd hunger bar does not go down throughout that whole time. On top of that when it heals it helas 2 health instead of 1. 1 only happens occasionally. So I was wondering if I did something wrong or what?