I think you mean epidemiological. Many control for fast food consumption. Have you read them?

Also there are LOTS of human RCTs that show that plant fats (including seed oils) are healthier than animal fats, and that plant proteins are healthier than animal proteins (mostly bc they are lower in methionine).

You might want to read more paleoanthropology. Early humans (and genus Homo) were hunter/gatherers. Modern hunter/gatherers get most of their calories (and a boatload of fiber) from plants. Hunting is a great resource, but very intermittent. Our big hungry human brains don't run on meat... they run on sugar, in particular starch. What is on the savannah in Africa but not in the forest? Lots of starchy plants. Humans have evolved much more starch-digesting amylase enzyme in our saliva than any other animal on earth. Why would that be? We even evolved a unique bacteria in our mouth that eats that enzyme. Neanderthals had the same bacteria in their mouth... suggesting that starch eating was fundamental to our way of life from our common ancestor with them... Homo erectus or earlier.