For the past year I have concentrated heavily on my family genealogy, and now have over 20,000 names in my database going back to before 1700. One of the things I have repeatedly noticed is the longevity, and how it changed over 300 years.
During the 1700's, my family members routinely lived well into their 90's and even a few over 100. The exceptions were men killed in battle or hunting accidents, women in childbirth, and the occasional accidental death of a child. This trend persisted through folks born in the early 1800's up to about 1830. Those born after 1830 began to show somewhat shorter lifespans, maybe only into their mid 80's, and those born after 1880 seldom lived much past their mid 70's.
There were exceptions, of course. But the majority followed that pattern and I always wondered why.
My research into the historic diets of humans indicates a strong correlation to shorter lifespans as processed foods came into our diets, and that is supported in my own family history. Family members who were Pennsylvania Dutch ate a high animal fat diet (meat, butter, milk, eggs) along with their garden vegetables, and put up many gallons of fermented vegetables for the winter. They lived the longest.
Sugar was seldom part of the diets much before the Civil War (it was available, just expensive) except for fruits, berries and occasionally honey. Cereal grains were a portion of their diets, but generally in the form of fermented (sourdough) breads (or fermented as beer and whiskey), and slow-cooked cereals, although grains were not nearly as high a percentage of diet as after 1900.
I suspect the vegetables they ate were considerably higher in nutrient density solely because the soils back then were not abused and depleted of vital minerals. Because they depended on the land to support them, I believe they were good stewards. Their water was clean, clear potable water; the air was clean, and the soil healthy. There were no grocery stores full of junk foods and food additives. They ate Real Food.
(Some of my family were coal and zinc miners. I do not include them here as they lived in a horrid environment and lifespans were often curtailed by the mines.)
As more of my family moved to cities for work, their diets changed. My mother was born in 1921. My grandparents stopped owning a cow by the time my mother was 5 or so... farms in the dust belt were becoming non-productive and my family moved away. However, I can remember as a child about 1946 going across a field to an aunt's house to fetch a jug of milk from the ice cold water in her spring house in Kansas.
Many of my mother's generation lived into their 80's (including my mother) but they were not necessarily 'healthy' and drugs kept them going. How many folks do you know over 80 who do not take a handful of meds every day? In earlier generations there was almost no heart disease, no cancer, diabetes... they died of old age, not dis-ease.
The current interest of some of us to get back to healthy nutrition gives me a glimmer of hope for the sustainability of mankind.
ps... I found an interesting chart of US Presidents, longevity, death, and diet here. The doctor who wrote it makes the same correlation between longevity and diet as I do. (Scroll down a bit on the page, the chart stands out.)