The premise is simple: you start on half a heart, maximum. Every time you eat a *unique* food item, you gain half a heart. So the more you eat, the more health you have. Kind of like Spice of Life: carrot edition.
There is also an option to toggle such that your unique food list, and thus your health, resets upon death, for that very spicy fun.
Run /veryspicy true to turn this on, or /veryspicy false to turn this off.
Run /foodlist to see what foods you've eaten, and for ops, /foodlist_all to see what everyone has eaten (though it will only show UUIDs, this is not a bug and won't be changed, sorry)