This article is a continuation of last week's review of the North Karelia study, which linked reducing saturated fat to a decrease in deaths from heart disease. In the previous note, we explored counterarguments to this claim. This article goes further to provide additional points based on my original research.
First, it's worth noting that the Seven Countries Study (SCS) featured two cohorts in Finland: west Finland and North Karelia. Both cohorts had similar diets and cholesterol levels, but deaths from coronary heart disease were substantially different. Last week's note explained that war and displacement likely accounted for this discrepancy, not fat or cholesterol.
Secondly, the North Karelia study replaced butter with rapeseed oil, which contains plant sterols that lower cholesterol. However, plant sterols have been found to worsen heart disease. Therefore, the use of rapeseed oil in the study doesn't necessarily support the notion that reducing saturated fat intake is beneficial for heart health.
My PhD reviewed evidence from all randomised controlled trials (RCTs) that reduced dietary fat or saturated fat in favour of unsaturated fat. The RCTs that successfully lowered cholesterol levels, primarily through the plant sterol mechanism, failed to make any significant impact on mortality, whether from heart disease or other causes.
Finally, both Finland cohorts had the highest recorded average cholesterol levels of all 16 cohorts in the SCS. I suggest that this is because they are located furthest away from the equator - Natural sunlight hitting cholesterol in our skin cell membranes turns the cholesterol into vitamin D. With reduced sunlight, in countries further away from the equator, there is reduced sunlight to turn cholesterol into vitamin D.