Processed sugars are the enemy.
We were designed to eat stuff that walked on the ground, or came out of the ground/water.
Rendering, processing, concentrating were not on the original menu.
I would go beyond that: pasta and grapes are not processed any differently by your body than a glazed doughnut. It all winds up as glucose (except for the fructose which may even be worse). We didn’t eat wheat or oats or barley before 12,000 years ago.
Bingo. I have cut most of that crap out and virtually eliminated bread/processed wheat and I’ve lost 20% of my body weight over the last few months and cut my body fat to just around 10% with little change in my exercise regime. The foods we eat today are just not good for you.
Animals then didn't eat what farm fed animals eat today.
True, but we also are designed to eat one thing at a time whenever we could find it. There were no plates, dinner prep, or freezers. We found, we ate. Complex carbs are ok to eat too, but sparingly. When we found them, they were small bits of grain that we would eat slowly because they were so hard to gather. Grains would usually be a last resort when there was no game, fish or fruits.
Today's grilled cheese sandwich or cereal with milk cannot be processed by our digestive systems.