Key Findings
A major disadvantage when analyzing dietary fatty acids is the limited interpretation when compared to the more realistic analyses of specific oils and solid fats. Moreover, findings on dietary acids are more difficult to transfer into recommendations on primary prevention of non-communicable chronic diseases. To address this issue in the present systematic review, the methodology of network meta-analysis (NMA), which enables a simultaneous comparison of intervention trials was used in this study.
NMA combines direct (i.e., from trials comparing directly two interventions) and indirect (i.e., from a connected root via one more intermediate comparators) evidence in a network of trials. The aim of the present study was to compare the effects of 13 different oils and solid fats across randomized trials on established blood lipids (TC, LDL-C, HDL-cholesterol, and triacylglycerols) factors using NMA methodology. Safflower oil showed the highest SUCRA value for reduction in TC and LDL-C followed by rapeseed oil and sunflower oil; soybean oil was the most effective oil to reduce TG, followed by corn oil and palm oil; butter and lard were ranked worst for TC, LDL-C reduction; coconut oil was ranked best to improve HDL-C, followed by palm oil and beef fat. The NMA showed that all vegetable oils were more effective in reducing TC (-0.49 mmol/l to -0.18 mmol/l) and LDL-C (-0.42 mmol/l to -0.23 mmol/l) compared to butter. Most of the comparisons derived from mixed evidence were rated as moderate quality of evidence. With respect to potential mechanisms of action, the general cholesterol-lowering effects predominantly exerted by vegetable oils in the present study might be due to their fatty acid composition, specifically the contents of n-3 and n-6 PUFAs or MUFAs. Unsaturated fatty rich oils like safflower-, sunflower-, rapeseed-, flaxseed-, corn-, olive-, soybean-, palm-, and coconut-oil were more effective in reducing LDL-C (-0.42 mmol/l to -0.20 mmol/l) as compared to SFA-rich food like butter or lard. LDL-C predicted differences based on their fatty acid composition showed that each 10% of dietary energy from butter replaced by unsaturated fatty rich oils (-0.31 to -0.22 mmol/l) were in line with findings from the NMA. Despite limitations of the NMA approach, and the overall low-quality of evidence judgements, the NMA findings are in line with existing evidence on metabolic effects of fat, and support current recommendations to replace high saturated-fat food with unsaturated oils.
ABSTRACT
The aim of this network meta-analysis (NMA) is to compare the effects of different oils/solid fats on blood lipids. Literature searches were performed until March 2018. Inclusion criteria were as follows: i) Randomized trial (≥3 weeks study length) comparing at least two of the following oils/ solid fats: safflower-, sunflower-, rapeseed-, hempseed-, flaxseed-, corn-, olive-, soybean-, palm-, coconut-oil, lard, beef-fat, and butter; ii) LDL-cholesterol (LDL-C), total cholesterol (TC), HDL-cholesterol (HDL-C), and triacyglycerols (TG). A random dose-response (per 10% iso-caloric exchange) NMA was performed and surface under the cumulative ranking curve (SUCRA) was estimated. 54 trials were included in the NMA. Safflower-oil had the highest SUCRA value for LDL-C (82%) and TC (90%), followed by rapeseed-oil (76% for LDL-C, 85% for TC), whereas palm oil (74%) had the highest SUCRA value for TG, and coconut-oil (88%) for HDL-C. Safflower-, sunflower-, rapeseed-, flaxseed-, corn-, olive-, soybean-, palm-, and coconut-oil as well beef fat were more effective in reducing LDL-C (-0.42 mmol/l to -0.23 mmol/l) as compared to butter. Despite limitations in these data, our NMA findings are in line with existing evidence on metabolic effects of fat, and support current recommendations to replace high saturated-fat food with unsaturated oils.
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