I‘m pretty sure humans eat potato, rice, peas etc. since a pretty long time.
I‘m also pretty sure that the meat our ancestors ate is a lit different from the meat we have now coming from animals optimized for meat production and fed with whatever produces the most meat and costs the least (mad cow disease anyone?).Not to mention the amount of meat we eat today compared to back then.
The problem with processed food isn’t that it is processed but that it makes it easy to consume too much