A systematic review of randomized trials was recently published in the Annals of Internal Medicine, describing the associations between saturated fat intake and cholesterol, mortality, and major cardiovascular events. It included 17 eligible trials and over 66,000 participants, including people with and without cardiovascular disease.
Overall, reducing saturated fat intake was associated with non-significant reductions in both all-cause and cardiovascular mortality, as well as non-fatal myocardial infarctions and both fatal and non-fatal strokes. Rather than using a relative risk reduction as their standard, the authors used a threshold of an absolute benefit of at least 5 for fatal events and 10 for non-fatal events per 1000 within 5 years, and concluded that reducing saturated fat intake did not meet this threshold among people with low baseline cardiovascular risk. However, among people with higher baseline cardiovascular risk, the absolute benefits were above this threshold, with the strongest signal reported as a significant 25% reduction in the risk for non-fatal myocardial infarction when saturated fat was replaced with polyunsaturated fat.
There were a number of limitations to this systematic review (which had low to moderate certainty), including limited data on the effect of replacing saturated fat with monounsaturated fat or protein, the limited time frame (5 years) to observe any benefits, as well as heterogeneity among studies and the variable adherence to a low saturated fat diet, i.e., an intervention may appear ineffective if not well implemented. The ambiguity on this topic has plagued researchers for years, in part because what saturated fat is replaced with matters, and in some studies, saturated fat (and fat) intake has been conflated with calorie intake. In poorer areas, this may be a signal for adequate calorie intake. Nonetheless, this study suggests that among people with low baseline risk, the absolute benefits are likely to be low, at least in the short term.