Many people in these remote areas stayed perfectly thin and healthy till their 90+ or ever 100+ years old. And they were essentially diabetes-free, cancer-free, and heart-disease-free. Essentially all the instances of diabetes, cancer, and heart disease between 1850s-1950s were among wealthier people in cities who were overeating on carbs/sugar and were developing diabetes (often followed by heart disease or cancer) in a manner similar to how people do today.

So what did these people in remote areas eat? They all ate lots of meat and/or fish (if they were by the ocean). Remote areas often had harsh/cold climate, so there were no fresh vegetables at all between the fall and summer. They also ate zero seed oils (they did not exist at the time).

The other common food items were - potatoes, sweet potatoes, rice, beans, vegetables and berries in the summer. Grains varied by the region.

People in remote areas often ate twice a day - breakfast and dinner (since they were often working outside during the day).

Almost all the food people ate was locally sourced. The only thing "imported" was generally spices. Sugar was very expensive and not common.

Since we know what people in remote areas between 1850s and 1950s ate, and we know that many of them stayed perfectly healthy till their 90s or 100s (and why their causes of deaths earlier in their lives are completely irrelevant to us today), there is no reason why we should not copy the way they ate.

And I am not saying that all modern food is bad for you (although I am pretty sure that most of the modern food is in fact harmful to a various degree). The main point is that is does not matter. We know for a fact that the way people ate in various remote areas between 1850s-1950s was exceptionally healthy and led to exceptional levels of longevity; so why not take that a starting point.