When I jumped down from something I had expected to lose more hearts than I did, but I realized that I had eaten an extra food earlier (when my health bar was already full I ate another food).
...So did an experiment:
-First, I built a twenty-one block height tower, which deals exactly nine out of ten hearts when player has full health.
-Second, when hurt I ate bread but without removing my finger from the screen I ate another bread when already at full health. This visually did nothing but make me lose another bread.
-Lastly, I fell from the tower again. Instead of leaving me with only one heart left, it left me with three and a half hearts.
So what I'm thinking, is that when the player is able to eat an extra bit of food when already at full health the hearts the food heals will almost 'bank' over until the player takes damage. Giving the player extra hearts.