There’s an article in the LA Times today talking about early North Americans being forced to change their diet to incorporate more plant life when the woolly mammoth and other megafauna began dying off. “When the woolly mammoth ran out, early man turned to roasted vegetables”:
Long before early humans in North America grew corn and beans, they were harvesting and cooking the bulbs of lilies, wild onions and other plants, roasting them for days over hot rocks, according to a Texas archaeologist.[...]
Meadowlands and forest edges were filled with lilies, wild onions and perhaps two dozen other wild plants ready for the harvesting. The bulbs of these plants are about as nutritious as sweet potatoes, but their energy is locked up in a dense, indigestible carbohydrate called inulin. The only way to make the bulbs digestible is to roast them for two days or longer.