Cholesterol and Blood Lipids Systematic Literature Review

Cholesterol and Blood Lipids

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Reference: Ghobadi, S., et al., Comparison of blood lipid-lowering effects of olive oil and other plant oils: A systematic review and meta-analysis of 27 randomized placebo-controlled clinical trials. Crit Rev Food Sci Nutr, 2018: p. 1-15.

One-sentence summary: Olive oil consumption decreased total cholesterol (TC), LDL cholesterol (LDL-C), and triglycerides (TG) significantly less than other plant oils, and increased HDL cholesterol (HDL-C) significantly more than other plant oils.

Study type: A systematic review and meta-analysis of 27 randomised controlled clinical trials of at least 2 weeks duration.

Diet: At least 10 grams of olive oil per day, compared to another plant oil as the control. For the olive oil arm, virgin olive oil was used in 11 studies, refined olive oil in 6 studies, and the remaining studies did not provide information about the olive oil type. The plant oil control was rapeseed oil in 8 studies, sunflower oil in 6 studies, corn oil in 4 studies, palm oil in 3 studies, soya bean oil in 3 studies, flaxseed oil in 2 studies, and another plant oil used in a single study including soy bean/safflower, sesame, primrose, camellia, peanut and rice oil.

Oils were classified into the following categories:

  • n-3 rich oils = soya bean, rapeseed and flaxseed oil
  • n-6 rich oils = corn, sunflower and primrose oil
  • saturated fatty acid (SFA) rich oils = palm oil and
  • Miscellaneous oils = argan, sesame, camellia, rice bran oil and mixture of soya bean and safflower oil

Outcomes measured: One or more of the following lipid profile measures:

  • HDL- cholesterol (HDL-c)
  • LDL cholesterol (LDL-c)
  • Total cholesterol (TC)
  • Triglycerides (TG)
  • Apolipoprotein A (Apo A)
  • Apolipoprotein B (Apo B)

 

Population:

Studies in adults, mostly from European countries (14 studies), followed by the USA (7 studies), Asia (2 studies), Australia and Africa (1 study each). More than half of the studies enrolled healthy subjects, whilst nine studies were carried out on patients with hyperlipidemia and the other studies included patients with non-alcoholic fatty liver disease, metabolic syndrome, peripheral vascular disease and rheumatoid arthritis.

 Key results:

  • HDL- cholesterol (HDL-c): olive oil increased HDL-c significantly more vs. all other plant oils (weighted mean difference [WMD] = 1.37 mg/dl: 95% CI: 0.4, 2.36; P = 0.007) (n = 26 studies).
    • Control group: olive oil increased HDL-c significantly more vs. n-3 rich oils (WMD = 1.9 mg/dl: 95% CI: 0.5, 3.25; P = 0.008) (12 studies) and vs. miscellaneous oils (WMD = 4.11 mg/dl: 95% CI: 0.95, 7.3; P = 0.01) (5 studies), but no difference vs. n-6 oils (n = 11 studies) or SFA rich oils (3 studies).
    • Intervention duration: olive oil increased HDL-c significantly more vs. all other plant oils in interventions > 30 days duration (WMD = 1.77 mg/dl: 95% CI: 0.28, 3.27; P = 0.02) (11 studies), but there was no difference in studies ≤ 30 days duration (15 studies).
    • Age: olive oil increased HDL-c significantly more vs. all other plant oils in persons ≤ 50 years (WMD = 1.55 mg/dl: 95% CI: 0.4, 2.7; P = 0.01) (15 studies), but no difference in persons > 50 years (11 studies).
    • Lipid status: olive oil increased HDL-c significantly more vs. all other plant oils in normolipemic persons (WMD = 1.5 mg/dl: 95% CI: 0.17, 2.8; P = 0.03) (15 studies), but no difference in persons with hyperlipidaemia (7 studies).
  • LDL cholesterol (LDL-c): olive oil decreased LDL-c significantly less vs. other plant oils (WMD= 4.2 mg/dl: 95% CI: 1.4, 7.01; P = 0.003) (24 studies).
    • Control group: olive oil decreased LDL-c significantly less compared to miscellaneous oils (WMD = 6.43 mg/dl: 95% CI: 2, 11; P = 0.005) (5 studies), but there was no difference in the reduction vs. W3 oils (12 studies), W6 oils (10 studies) or SFA rich oils (3 studies).
    • Intervention duration: olive oil decreased LDL-c less vs. all other plant oils in interventions ≤ 30 days duration (WMD = 7.1 mg/dl: 95% CI: 3.8, 10.4; P = 0.001) (15 studies), but there was no differences in studies > 30 days duration (10 studies).
    • Age: olive oil decreased LDL-c significantly less vs. all other plant oils in persons ≤ 50 years (WMD = 6.95 mg/dl: 95% CI: 4.2, 9.7; P = 0.001) (13 studies), but there was no difference in persons > 50 years (12 studies).
    • Lipid status: olive oil decreased LDL-c significantly less vs. all other plant oils in normolipemic persons (WMD = 5.9 mg/dl: 95% CI: 2.65, 9.1; P = 0.001) (14 studies), but no difference in persons with hyperlipidaemia (8 studies).
  • Total cholesterol (TC): olive oil decreased TC significantly less vs. other plant oils (WMD= 6.27 mg/dl: 95% CI: 2.8, 10.6; P = 0.001) (26 studies).
    • Control group: olive oil decreased TC significantly less compared to W3 rich oils (WMD = 6.4 mg/dl: 95% CI: 2, 10.87; P = 0.005) (11 studies), W6 rich oils (WMD = 9.9 mg/dl: 95% CI: 2.75, 17; P = 0.007) (12 studies) and miscellaneous oils (WMD = 6.5 mg/dl: 95% CI: 1.11, 11.8; P = 0.02) (5 studies), but no difference vs. SFA rich oils (3 studies).
    • Intervention duration: olive oil decreased LDL-c less vs. all other plant oils in interventions ≤ 30 days duration (WMD = 8.23 mg/dl: 95% CI: 4.13, 12.3; P = 0.001) (14 studies), but no differences in studies > 30 days duration (11 studies).
    • Age: olive oil decreased LDL-c significantly less vs. all other plant oils in persons ≤ 50 years (WMD = 8.1mg/dl: 95% CI: 4.6, 11.7; P = 0.001) (14 studies), but no difference in persons > 50 years (12 studies).
    • Lipid status: olive oil decreased LDL-c significantly less vs. all other plant oils in both normolipemic persons (WMD = 6.9 mg/dl: 95% CI: 2.27, 11.5; P = 0.003) (14 studies) and persons with hyperlipidaemia (WMD = 8.1 mg/dl: 95% CI: 0.44, 15.7; P = 0.038) (9 studies).
  • Triglycerides (TG): olive oil decreased TG significantly less vs. other plant oils (WMD = 4.31 mg/dl: 95% CI: 0.5, 8.12; P = 0.03) (25 studies).
    • Control group: olive oil decreased TG significantly less compared to W3 rich oils (WMD = 8.32 mg/dl: 95% CI: 2.66, 13.9; P = 0.004) (11 studies), but no difference vs. W6 oils (10 studies), miscellaneous oils (5 studies) or SFA rich oils (3 studies).
    • Intervention duration: No differences in olive oil arm vs. plant oil arm in studies > 30 days duration (11 studies) or in studies ≤ 30 days duration (14 studies).
    • Age: No differences in olive oil arm vs. plant oil arm in persons ≤ 50 years (14 studies) or in persons > 50 years (11 studies).
    • Lipid status: No differences in olive oil arm vs. plant oil arm in normolipemic persons (14 studies) or in persons with hyperlipidaemia (7 studies).
  • Apolipoprotein A (Apo A): No significant change for olive oil vs. other plant oils.
  • Apolipoprotein B (Apo B): No significant change for olive oil vs. other plant oils.

 

Quality assessment: The risk of bias and quality assessment was done according to the Cochrane collaboration criteria, with the majority of studies receiving a low risk of bias for the majority of assessment guidelines. There was no sign of publication bias for HDL-c, LDL-c, TC and TG outcomes.

Limitations: The diets consumed during intervention were not controlled and constant among all interventions, with many studies not reporting its energy and macronutrient composition.

The bottom line: Olive oil was less potent in lowering TC, LDL-C, and TG than other plant oils. This difference was more evident for PUFAs- rich oils, especially n-3 rich ones. However, time was an important variable. The differences in reduction of TC, LDL-C, and TG compared to other plant oils were not evident in interventions with durations higher than 30 days. Olive oil increased HDL-cholesterol to a greater extent than other plant oils, including in studies longer than 30 days.

 

Other reviews:

George, E.S., et al., The effect of high-polyphenol extra virgin olive oil on cardiovascular risk factors: a systematic review and meta-analysis. Crit Rev Food Sci Nutr, 2018: p. 1-138.

Hohmann, C.D., et al., Effects of high phenolic olive oil on cardiovascular risk factors: A systematic review and meta-analysis. Phytomedicine, 2015. 22(6): p. 631-40.

Nordmann, A.J., et al., Meta-analysis comparing Mediterranean to low-fat diets for modification of cardiovascular risk factors. Am J Med, 2011. 124(9): p. 841-51 e2.

Serra-Majem, L., B. Roman, and R. Estruch, Scientific evidence of interventions using the Mediterranean diet: a systematic review. Nutr Rev, 2006. 64(2 Pt 2): p. S27-47.

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