METHODS AND STUDY DESIGN: We searched Medline, Embase, Cochrane Central Registry of Controlled Trials and CINAHL. Clinical trials were eligible if they compared palm oil-rich diets with diets rich in MUFAs or PUFAs. We pooled results of included studies using a random effects model and assessed the quality of the evidence and certainty of conclusions using the GRADE approach.
RESULTS: Intake of palm oil intake compared to oils rich in MUFA was associated with increased levels of total cholesterol (TC) [mean difference (MD)=0.27 mmol/L; 95% CI 0.08 to 0.45], LDL-C (MD=0.20 mmol/L; 95% CI 0.02 to 0.37) and HDL-C (MD=0.06 mmol/L; 95% CI 0.02 to 0.10). Similarly, for comparison with oils rich in PUFAs, palm oil showed increased in TC (MD=0.38 mmol/L; 95% CI 0.14 to 0.62), LDL-C (MD= 0.44 mmol/L; 95% CI 0.01 to 0.88) and HDL-C (MD=0.08 mmol/L; 95% CI 0.03 to 0.13). For both comparisons, there were no significant effects on triglycerides.
CONCLUSIONS: Even though palm oil increases marginally the level of serum lipids, the evidence is mostly of low to moderate quality.
METHODS: The blends were prepared in a volume ratio of 10:90, 20:80, 40:60, and 60:40 (RBO:SO). The changes in the oxidative parameters and fatty acid composition of the samples during heating at frying temperature (170°C) were determined using analytical and instrumental methods. Oxidative alteration was also monitored by recording FTIR spectra of oil samples.
RESULTS: The increase in oxidative parameters (free fatty acid, color, specific extinctions, peroxide value, p-anisidine value, and thiobarbituric acid value) was greater in pure SO as compared to RBO or blend oils during heating. This indicates that the SO samples incorporated with RBO have the least degradation, while pure SO has the highest. Blending resulted in a lower level of polyunsaturated fatty acids (PUFA) with a higher level of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA). During heating, the relative content of PUFA decreased and that of SFA increased. However, the presence of RBO in SO slowed down the oxidative deterioration of PUFA. In FTIR, the peak intensities in SO were markedly changed in comparison with blend oils during heating. The reduction in the formation of oxidative products in SO during thermal treatment increased as the concentration of the RBO in SO increased; however, the levels of the protective effect of RBO did not increase steadily with an increase in its concentration.
CONCLUSIONS: During thermal treatment, the generation of hydroperoxides, their degradation and formation of secondary oxidative products as evaluated by oxidative indices, fatty acids and IR absorbances were lower in blend oils compared to pure SO. In conclusion, RBO can significantly retard the process of lipid peroxidation in SO during heating at frying temperature.