Minecraft wiki entry for Development_versions, associated text: Are now balanced to improve gameplay.
Instant Health nerfed by 33% (heals only 4 health points/2 hearts at level I).
Regeneration nerfed by 50% (takes 50 ticks/2.5 seconds to restore 1 health point/.5 heart at level I).
Natural health regeneration now costs hunger points/saturation points.