I think in the end it's all going to be about things like CAFO, processed, and added sugars. I was born in 1955 which means that while I ate CAFO chicken (which started in the 50s), beef and pork weren't CAFO until the 1970s, so I got to eat relatively healthy food through puberty. My grandparents didn't eat CAFO until they were already grandparents. I bring this up because in my family it was usual to live to be 85+ until my mother's generation. Coincidentally, that was the generation that fell in love with convenience foods like tv dinners, canned soups and sauces, etc. It also coincides with the proliferation of fast food places like McD and their ilk.
It's not scientific, but observationally, what I see is that the generations that ate tomato sauce made from tomatoes (not premade in a can), produce not shipped from 1500 miles away, real olive oil, homemade wine, and meats that weren't CAFO lived longer than the next generation. And they ate plenty of wheat in the form of pasta and doughs that stretched meat out for large families.
"Right is right, even if no one is doing it; wrong is wrong, even if everyone is doing it." - St. Augustine