I found the following in "Omega-3 Oils, a practical guide" by Donald Rudin,
MD.  Thought it was a great example for Paleo:

"The most clearly documented example of what happens when a society returns
to a traditional diet occurred by chance in Norway during World war II.
The incidence of schizophrenia, cancer and heart disease had doubled in
that country after 1900, when Norwegians abandoned their traditional diet
in favor of processed foods. Yet in the early 1940s, the incidence of these
illnesses declined a startling 40 percent. That decline coincided exactly
with the years of hardship during the German Occupation of Norway.
   What happened to the Norwegian diet during those terrible years?
Because of the occupation, processed and refined foods were scarce, forcing
the Norwegians 5to revert to eating traditional foods. Beans, whole grains,
and fish--once staples in the diet--again became daily fare.  Scientists
who studied the phenomenon, which I call the Norwegian notch, found that
40-percent decrease in schizophrenia, heart disease, and cancer coincided
with a 50-percent increase in consumption of Omega-3 fatty acids. Fiber
consumption probably also increased, and we know margarine consumption fell
to very low levels.
    After the war, the Norwegians reverted to eating commercial and
processed foods. Rates of heart disease and schizophrenia soon climbed back
to prewar levels."

**I would think that the reporting of health conditions during that time
was not the best, but it is still very interesting.

Bob