Systematic Literature Reviews

A review of recent systematic literature reviews

Prepared for Olive Wellness Institute

July 2018

Prepared by Nutrition Research Australia

Aim

The aim of this project was to:

  • Search the literature for systematic literature reviews (SLRs) or meta-analyses on olive oil and/or the Mediterranean Diet
  • Provide a brief summary of the SLRs for ten health outcomes to be used to update the Olive Wellness Institute (OWI) website

 

Methodology

The following methodology was used to obtain all SLRs on olive oil and/or the Mediterranean diet:

  • PUBMED and Web of Science databases were searched for studies published from the year 2000 to June 2018.
    • The search was limited from the year 2000, as all previously published reviews would be outdated, and all previous studies would be captured in more recent reviews of the literature.
  • Search terms included: Mediterranean diet OR Mediterranean OR Olive oil OR Extra virgin olive oil OR Virgin olive oil OR EVOO OR VOO AND Review OR Systematic review OR Systematic literature review OR SLR OR Meta-analysis OR Meta-analyses.
    • Limited to reviews in English and in humans (children or adults).
  • Titles and abstracts were scanned for the following inclusion criteria:
    • Systematic reviews or meta-analysis.
      • Expert/narrative reviews or individual studies were not considered.
    • Reviews focused specifically on the Mediterranean diet or on olive oil (any type)
      • This included reviews that looked at the Mediterranean diet alongside other diets.
    • Any health outcome or related measure (e.g. adherence, cost-effectiveness, etc.).
  • Studies were categorised into 14 health outcomes, and ten outcomes were included in this summary report.
    • Asthma (excluded)
    • Blood pressure
    • Bone health (excluded)
    • Cancer risk (excluded)
    • Cardiovascular disease
    • Cholesterol and lipids
    • Cognitive health and impairment
    • Depression and mental health
    • Type 2 diabetes (prevention and management)
    • Frailty in the elderly (excluded)
    • Inflammation
    • Metabolic Syndrome
    • Mortality (excluded)
    • Rheumatoid arthritis
    • Weight and anthropometric measures
  • The most recent and relevant review was selected and summarised for each of the ten health outcomes.
    • Studies were chosen based on:
      • Diet: Studies specifically on olive oil were prioritised over those on the Mediterranean diet, when available
      • Publication date: Studies with the most recent publication date
      • Outcomes: Studies that reported the largest range of measures relevant to the outcomes of interest (i.e. more than one risk factor for cardiovascular disease)
      • Quantitative assessment: Studies that performed a meta-analysis
      • Quality of evidence: Highest quality of evidence (i.e. RCTs prioritised over cross-sectional studies)
      • Impact factor: Studies published in a journal with the highest impact factor of the journal
      • Citations: When studies had a similar publication date, those with the greatest number of citations
    • Data were obtained for each paper on:
      • Study type
      • Diet or food investigated
      • Outcomes measured
      • Population studied
      • Key study results
      • Quality assessment
    • Upon assessment of the review, we provided:
      • A one-sentence summary
      • A list of its limitations
      • The bottom line of what the research means
    • The other review papers identified via the literature search are listed at the end of each health outcome section.

 

Results

Click on the below links to access a summary of each area investigated:

*Click on a body part to see health benefits

human-body-infographic

Blood pressure

Cognitive health & impairment

Inflammation

Cardiovascular disease

Depression & mental health

Metabolic syndrome

Weight & anthropometric

Cholesterol & blood lipids

Type 2 diabetes

Rheumatoid arthritis

High phenolic olive oils lead to a small reduction in systolic but not diastolic blood pressure and oxidized LDL compared to low phenolic olive oils, and there was no difference in cholesterol, triglycerides and malondialdehyde.
Key reference: 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.
A Mediterranean diet reduced the risk of cognitive impairment and dementia, and was associated with improved cognitive functioning.
Key reference: Petersson, S.D. and E. Philippou, Mediterranean Diet, Cognitive Function, and Dementia: A Systematic Review of the Evidence. Adv Nutr, 2016. 7(5): p. 889-904.
Evidence from randomised controlled trials shows olive oil exerts beneficial effects on markers of inflammation and endothelial function.
Key reference: Schwingshackl, L., M. Christoph, and G. Hoffmann, Effects of Olive Oil on Markers of Inflammation and Endothelial Function-A Systematic Review and Meta-Analysis. Nutrients, 2015. 7(9): p. 7651-75.
Olive oil consumption significantly reduced the risk of cardiovascular disease (CVD) risk and stroke, but not specifically for coronary heart disease (CHD) risk.
Key reference: Martinez-Gonzalez, M.A., L.J. Dominguez, and M. Delgado-Rodriguez, Olive oil consumption and risk of CHD and/or stroke: a meta-analysis of case-control, cohort and intervention studies. Br J Nutr, 2014. 112(2): p. 248-59.
Any high diet quality, including a Mediterranean diet specifically, was associated with a reduction in the incidence of depressive symptoms, but a causal relationship is not yet established.
Key reference: Molendijk, M., et al., Diet quality and depression risk: A systematic review and dose-response meta-analysis of prospective studies. J Affect Disord, 2018. 226: p. 346-354.
The Mediterranean diet was inversely associated with metabolic syndrome, although the data are limited and come mostly from cross-sectional studies.
Key reference: Godos, J., et al., Adherence to the Mediterranean diet is inversely associated with metabolic syndrome occurrence: a meta-analysis of observational studies. Int J Food Sci Nutr, 2017. 68(2): p. 138-148.
The Mediterranean diet was efficacious for long-term weight loss in overweight or obese individuals compared with low-fat diets, but not compared with other diets (a low carbohydrate diet or the American Diabetes Association diet).
Key reference: Mancini, J.G., et al., Systematic Review of the Mediterranean Diet for Long-Term Weight Loss. Am J Med, 2016. 129(4): p. 407-415 e4.
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.
Key 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.
High olive oil intake was associated with a decreased risk of T2D and improved glucose metabolism in persons with T2D.
Key reference: Schwingshackl, L., et al., Olive oil in the prevention and management of type 2 diabetes mellitus: a systematic review and meta-analysis of cohort studies and intervention trials. Nutr Diabetes, 2017. 7(4): p. e262.
There was insufficient evidence to support the use of the Mediterranean Diet for the prevention of rheumatoid arthritis, but it may provide some benefit for the progression of rheumatoid arthritis.
Key reference: Forsyth, C., et al., The effects of the Mediterranean diet on rheumatoid arthritis prevention and treatment: a systematic review of human prospective studies. Rheumatol Int, 2018. 38(5): p. 737-747.

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