> On the other hand it's almost impossible to imagine what food was like in the Americas before Columbus.

Not at all. Many pre columbian foods remain popular today, like tamales. Corn, beans, squash, fish, nuts, and tropical fruit were all staple foods in pre contact Mesoamerica. Central American islanders were big on grilling fish over coals.

I don't think it was a miserably plain diet by any means.