This paper by J. A. J. Gowlett is a short overview of what we know about the diet of our species.

I was surprised to learn we've been eating roots and tubers for millions of years:

Comparisons of diet with living apes and modern peoples using similar ranges of plant foods in Africa suggest that a major factor in the change was adoption of roots and tubers in the diet [4, 12]. This addition to the diet was probably necessitated by the need to gain food at all times in a more seasonal environment (the savannah), and it places starchy carbohydrate consumption as part of the deep ancestry of human beings.

From some quick research, two starches early humans had in their diet were wild sorghum and wild African 'potato'.

Also made me wonder if it's wise to consume as much dairy products as I currently do:

[...] no ancient population would have been heavily dependent on milk or other dairy products—all that belongs to the last 5000 years.