It has been suggested that polyphenols in unrefined coconut oil may be beneficial for improving inflammation and glucose homeostasis.22 Most of the studies included in our meta-analysis did not report on the types of coconut oil used. I2 values of 25%, 50%, and 75% indicated low, moderate and high degrees of heterogeneity, respectively.32. When these data were unavailable, end-of-treatment differences were used. Although coconut oil increases plasma HDL cholesterol, it is impossible to know if this is a beneficial mechanism in cardiovascular disease.7 Although HDL cholesterol is a robust risk marker for cardiovascular disease, genetic studies and HDL-raising drugs have not so far supported a causal relationship between HDL cholesterol and cardiovascular disease. To mitigate the unit-of-analysis error from including trials with multiple comparison arms, we combined the relevant control arms to create a single pairwise comparison.29 For example, we combined data from the chia oil, safflower oil, and soybean oil arms from a trial20 for a single pairwise comparison between coconut oil and combined nontropical vegetable oil interventions. In contrast to HDL, the role of LDL in promoting atherosclerotic CVD has been consistently demonstrated based on findings from Mendelian randomization studies41,43 and different LDL-cholesterol–lowering treatments.35, The apparent lack of causality for HDL-cholesterol concentrations in CHD led to the hypothesis that the heterogeneous apolipoprotein composition of HDL may affect reverse cholesterol transport differently.44 A potential cardioprotective mechanism of dietary unsaturated fat compared with saturated fat is the increase in HDL subspecies containing apolipoprotein E, which has been shown to facilitate all steps of reverse cholesterol transport.45 Therefore while saturated fat intake increases HDL-concentrations per se more than unsaturated fat,33 average HDL-concentrations may not be effective in reflecting HDL function or CHD risk.44, Proponents of coconut oil consumption argue that CVD is uncommon among populations who consume coconut as a staple, such as the Pukapukans and Tokelauan populations who obtain 34% and 63%, respectively, of daily energy intake from coconut.46 Tokelauan individuals who migrated to New Zealand had higher total cholesterol, LDL-cholesterol, and lower HDL-cholesterol levels than those who remained in Tokelau, despite having a lower saturated fat intake.47 However, these findings must be treated with caution because of the observational and ecological nature of the studies with a high potential for confounding by the traditional diets of these populations typically containing high amounts of fish and low amounts of processed foods.38. There was no evidence of benefits of coconut oil over nontropical vegetable oils for adiposity or glycemic and inflammatory markers. Even in comparison with palm oil, another tropical oil with high saturated fat content, coconut oil increased LDL cholesterol. In a network meta-analysis comparing multiple cooking fats, coconut oil did not significantly increase LDL-cholesterol as compared with nontropical vegetable oils.25 Network meta-analysis can theoretically strengthen the evidence base as a result of combining both direct and indirect comparisons, although this approach is not free from potential bias.39 However, the authors of the network meta-analysis included only 6 trials on coconut oil compared with our analysis that included 16 trials that compared coconut oil with nontropical vegetable oils and 4 trials with palm oil.25 The search for the network meta-analysis was conducted until March 2018, and 3 new trials have been published since then. Major lipids, apolipoproteins, and risk of vascular disease. Coconut oil is high in saturated fat and may, therefore, raise serum cholesterol concentrations, but beneficial effects on other cardiovascular risk factors have also been suggested. Such a trial is unlikely to be attempted because of the high cost of hundreds of millions of dollars, large numbers of participants, and many years of treatment with coconut oil and an appropriate control fat. All the authors made critical revisions to the manuscript for important intellectual content. NUS Graduate School of Integrative Sciences and Engineering (J.Y.H.S., R.M.v.D. screened the titles and abstracts of all articles initially identified, according to the eligibility criteria. Further, we assessed the stability of the pooled estimates by excluding the trials that were nonrandomized8,10 and weight-loss intervention trials.6,20 Stata version 12 (StataCorp) was used for statistical analyses. Assessing the quality of reports of randomized clinical trials: is blinding necessary? This should inform choices about coconut oil consumption. However, after excluding this trial, the summary effect of replacement of coconut oil with nontropical vegetable oil on LDL-cholesterol remained significant (7.53 mg/dL, 95% CI, 2.24–12.83; I2=65%). Conversion factor: LDL, HDL, and total cholesterol from mg/dL to mmol/L: divide by 38.67; and triglycerides: 88.57. Differential effects of medium- and long-chain saturated fatty acids on blood lipid profile: a systematic review and meta-analysis. The effect of coconut oil consumption on cardiovascular risk factors: a systematic review and meta-analysis of clinical trials. Is sushi ‘healthy’? All authors read and approved the final manuscript. https://doi.org/10.1161/CIRCULATIONAHA.119.043052, National Center The hypercholesterolemic effect of coconut oil intake is probably attributable to its high saturated fat content.33 In a recent meta-regression analysis, lauric acid, myristic acid, and palmitic acid, which together constitute about 70% of coconut oil,2 all increased LDL-cholesterol significantly compared with carbohydrate intake.34 The 10.47 mg/dL increase in LDL-cholesterol resulting from the replacement of nontropical vegetable oils with coconut oil may translate to a 6% increase in risk of major vascular events35 and a 5.4% increase in the risk of coronary heart disease (CHD) mortality.36 Similarly, replacing 5% of energy intake from saturated fat with polyunsaturated fat (the predominant fat in most nontropical vegetable oils) has been associated with 13% and 10% lower risk of CHD in epidemiological studies and clinical trials, respectively.1,37 Our results on adverse effects of coconut oil as compared with alternative cooking oils on LDL-cholesterol concentrations thus align with dietary recommendations to replace saturated fat with polyunsaturated fat.3 Concordant with our findings, authors of a previous systematic review of 8 trials that did not include a meta-analysis concluded that coconut oil raised LDL-cholesterol compared with nontropical vegetable oils and that there was no convincing evidence to support the consumption of coconut oil over nontropical vegetable oils for CVD risk reduction.38.
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