If I'm trying to sort out any sort of health info I will often look to longitudinal studies, ideally ones that are large in scale and include a wide range of ethnicities.
While the "7 Countries Studies" has a major flaw -- only men were included! -- it spawned many related studies.
My layperson's reading is why I have tried to follow the Mediterranean Diet for ~ 20 years now, though a traditional Japanese diet also scores very well in terms of low rates of heart disease and cancer.
My HDL and taste buds seem happy with it and my weight stays pretty stable, so I'll stick with it for another 20 unless things change. [Though I am eternally trying to add more fruits/veg and lower my cheese consumption!]
Study overview from the University of Minnesota School of Public Health: http://www.sph.umn.edu/epi/history/overview.asp
Random synopsis:
>The [1960s] 7 countries study instigated by Professor Ancel Keys documented the diets of 13,000 middle-aged men aged 40-59 living in Southern Italy, Greece (Crete, Corfu), Yugoslavia, Finland, Netherlands, Japan and US (about 70% of the men lived in rural areas).
>This study showed clearly that populations who ate the most saturated fat (Finland) had the highest levels of blood cholesterol and the most Coronary Heart Disease (CHD). This study also awakened the interest that the Cretan and Japanese diets may be related to the lower incidence of CHD and colon, prostate and breast cancer in these countries.