I once applied effect "Health Boost" level 46 and had the effect removed via entering the Exit Portal in The End dimension.

However, while the effect was removed, the black hearts were not removed along with it. Filling the hunger bar to full will only heal the player to 20HP (10 ❤) and not filling up the remaining hearts.

Note: This bug is NOT RELATED to |MC-6431 Losing status effects when returning to the overworld from the exit end portal - Jira (mojang.com)]