ReviewSaturated fat and cardiovascular disease: The discrepancy between the scientific literature and dietary advice
Introduction
Consumption of saturated fat increases levels of low-density lipoprotein (LDL) cholesterol [1]. LDL cholesterol has been positively associated with cardiovascular disease (CVD) risk [2]. These findings have led to worldwide recommendations to decrease the consumption of saturated fat to decrease the risk of CVD. The dietary guidelines, published by the U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services (USDHHS) in 2010 [3], have been criticized for being based on an incomplete body of relevant science and for inaccurately representing or summarizing the science on saturated fat in relation to CVD [4].
To examine the possible inconsistencies between findings in the scientific literature and the dietary advice relating saturated fat to CVD, results from three reports by important U.S. and European advisory committees were compared with findings in the scientific literature. The reports included that by the USDA/USDHHS report, a report about dietary fats from the Institute of Medicine (IOM) in 2005 [5], and a report about dietary fats from the European Food Safety Authority (EFSA) in 2010 [6].
Recommendations from the advisory committees are as follows:
- •
Consume less than 10% of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fatty acids (MUFAs and PUFAs) [3].
- •
Keep the intake of saturated fatty acids as low as possible while consuming a nutritionally adequate diet [5].
- •
Saturated fat intake should be as low as possible [6].
The advisory committees included three types of studies as support for their recommendations:
- 1.
Controlled trials that showed that saturated fat consumption increases (LDL) cholesterol levels.
- 2.
Intervention studies that showed that the decrease of saturated fat and the simultaneous increase of polyunsaturated fat in the diet decrease CVD risk.
- 3.
Prospective cohort studies that showed a positive association between saturated fat intake and coronary heart disease (CHD) risk.
Not all advisory committees included all three types of studies in their results. Table 1 lists the types of studies used as evidence and the number of studies included in the results from each type of support.
Section snippets
What does the scientific literature tell us?
In 2003, a meta-analysis of 60 controlled trials was published relating dietary fat intake to serum cholesterol levels [1]. As of this writing, no systematic review examining the effect of saturated fat on serum cholesterol has since been published. The analysis showed that saturated fat increases the levels of LDL cholesterol and high-density lipoprotein (HDL) cholesterol compared with carbohydrates without changing the ratio of total to HDL cholesterol. The investigators noticed that, because
What does the scientific literature tell us?
In 2001, a systematic review of 14 randomized trials was published examining the effect of replacing saturated fats by polyunsaturated fats [9]. A significant protective effect against CVD risk was found, but no significant association was found with CVD mortality. No significant effects remained after exclusion of the results from the Oslo Diet–Heart Study [10], in which subjects from the intervention group were also randomized to fish consumption. Moreover, meta-regressions from this
What does the scientific literature tell us?
At least three systematic reviews of prospective studies were published examining the direct relation between saturated fat intake and CVD [15], [16], [17]. Meta-analyses showed a consistent lack of an association between saturated fat intake and CHD [15], [16], [17], stroke [17], or total CVD [17]. All three reviews were published after, or at approximately the same time as, the reports from the advisory committees, but the results from the individual prospective studies, included in these
Summary
Reports from all three advisory committees mentioned that saturated fat intake increases LDL cholesterol and included the effect of LDL cholesterol on CVD in the evidence for an association between saturated fat and CVD. Reports from two of the three advisory committees (IOM and EFSA) mentioned that saturated fat intake increases HDL cholesterol, but none of the reports considered the effect of HDL cholesterol on CVD in the evidence for an association between saturated fat and CVD, although a
Conclusion
The results and conclusions about saturated fat intake in relation to CVD, from leading advisory committees, do not reflect the available scientific literature.
Discussion
The EFSA report was the only one to include data from randomized trials about the substitution of dietary fats in the results. Three meta-analyses of randomized trials were published from 2009 through 2010 [15], [37], [38] at approximately the same time as the EFSA report was published. Two analyses, including data from seven [37] and eight [15] trials, found (non)significant protective effects of substituting polyunsaturated fat for saturated fat against CHD risk and CHD mortality, but both
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