Reduction In Saturated Fat Intake For Cardiovascular Disease, Cochrane Library, 19 May 2020
We were interested in assessing the direct evidence from trials of the effects of reducing saturated fats. … Randomised controlled trials only.
We included 15 randomised controlled trials (RCTs) (16 comparisons, 56,675 participants), that used a variety of interventions from providing all food to advice on reducing saturated fat.
The main study papers ranged in publication date from 1965 to 2006, but with supplementary publications included up to 2019.
The findings of this updated review suggest that reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events. Replacing the energy from saturated fat with polyunsaturated fat or carbohydrate appear to be useful strategies, while effects of replacement with monounsaturated fat are unclear. The reduction in combined cardiovascular events resulting from reducing saturated fat did not alter by study duration, sex or baseline level of cardiovascular risk, but greater reduction in saturated fat caused greater reductions in cardiovascular events.
I pulled this paragraph from their Background Section:
Keys 19501 proposed that the concentration of plasma cholesterol was proportional to dietary saturated fatty acids (SFA) intake. This relationship was confirmed in work by Hegsted (Hegsted 19652; Hegsted 20003), who published an equation explaining the relationship in 1965 and subsequently in 2000. The equation suggests that dietary saturated fat increases serum cholesterol and so increases cardiovascular (CV) risk, while polyunsaturated fats (PUFA) reduce both.
1 Keys A, Mickelsen O, Miller EV, Carleton B. The relation in man between cholesterol levels in the diet and in the blood. Science 1950;112(2899):79-81.
2 Hegsted DM, McGandy RB, Myers ML, Stare FJ. Quantitative effects of dietary fat on serum cholesterol in man. American Journal of Clinical Nutrition 1965;17(5):281-95.
3 Hegsted DM. From chick nutrition to nutrition policy. Annual Review of Nutrition 2000;20:1-19.
Cochrane’s 2020 analysis found:
Reducing saturated fat caused reductions in serum total and LDL cholesterol, which did not differ according to type of replacement. There was little or no effect of saturated fat reduction on serum HDL cholesterol or triglyceride. Data on lipid ratios, Lp(a) and HOMA were very limited and effects unclear, but SFA reduction appears to reduce glucose two hours after a glucose load.
So, from 1950 to 2020, about 70 years, the thinking was and remains … a diet high in saturated fat can increase serum cholesterol and can increase risk for cardiovascular events.