I remember reading the book “Fatu Hiva” by Thor Heyerdahl, about the island of the same name in the Pacific. He mentions the custom of the inhabitants of fermenting breadfruit in the ground for several years before eating it. One indigenous man is quoted as saying that he cannot digest food unless he has a portion of fermented breadfruit with it.

I haven’t tried it yet. I did start to ferment some breadfruit after reading the book. But that’s only been eight years ago - so not yet good to eat.