Before agriculture the human diet varied wildly by location. People didn’t eat what they wanted to eat, they ate whatever was available.
But grains, dairy and other specifically agriculture-produced foods weren’t part of that diet. Grains were available, in some areas, but only seasonally and in relatively small quantities. Same with most other types of plant foods. Except in the tropics and arctic, what people ate varied wildly over the course of a year.
I’m well aware that grains were not originally part of our original diet, until we went agricultural.
But neither necessarily were proteins highly available, as it wasn’t always easy getting our hands on food that can move. :)
We ate a lot of roots, since roots don’t run very far very fast and we used a lot of plants in our diet. Plants don’t necessarily imply grains. Grasses, roots, fruits, whatever we could grab and found delicious, basically.
Except the times we resorted to cannibalism. Those weren’t good times, I reckon.