In healthy adults, olive oil consumption appeared to lower the risk for developing type 2 diabetes, whereas daily olive oil ingestion improved glucose metabolism in adults who already had the disease, according to findings from a meta-analysis.
“In many studies, olive oil has been suspected to exert beneficial effects on health,” Lukas Schwingshackl, MSc, PhD, of the department of epidemiology at the German Institute of Human Nutrition in Berlin, and colleagues wrote. “It is an integral part of the Mediterranean diet, providing approximately two-thirds of vegetable fats in this kind of nutrition ... The major question is still not well answered [as to] which of the components of the Mediterranean diet is worthwhile to be adopted in countries with other dietary traditions, without having a local substitutional food.”
Schwingshackl and colleagues analyzed data from four cohort studies and 29 randomized controlled trials conducted in Europe (n = 22), North America (n = 8), Australia/New Zealand (n = 2) and Asia (n = 1). Study duration varied between 5.7 and 22 years for cohort studies (n = 183,370) and between 2 weeks and 4.1 years for randomized controlled trials (n = 3,698); mean ages ranged between age 33 years and age 67 years. Randomized controlled trials were stratified by three types: olive oil vs. low-fat diet; olive oil vs. polyunsaturated fatty acid-rich oils, and olive oil vs. fish oil.
Researchers performed three types of meta-analyses to investigate any association between olive oil consumption and type 2 diabetes risk: high vs. low-intake meta-analysis, dose-response meta-analysis and restricted cubic spline calculation for each study with more than three categories of exposure to examine for possible nonlinear associations.
In random-effects meta-analysis, researchers found the combined association of the use of olive oil was inversely associated with a lower risk for type 2 diabetes. Compared with the lowest olive oil intake category, those in the highest olive oil intake category saw a 16% reduced risk for developing type 2 diabetes (RR = 0.84; 95% CI, 0.77-0.92); however, researchers observed evidence of a nonlinear relationship. In the dose-response meta-analysis, researchers found that each 10-g daily increase in olive oil intake was associated with a 9% reduced risk (RR = 0.91; 95% CI, 0.87-0.95). Risk for developing type 2 diabetes decreased by 13% with increasing olive oil consumption up to 15 g to 20 g per day; however, there was no observed benefit beyond this value, according to researchers.
In participants with type 2 diabetes, olive oil interventions resulted in a greater reduction in HbA1c vs. controls (mean difference, –0.27%; 95% CI, –0.37 to –0.17). In subgroup analyses, the effect persisted only when compared with low-fat diets (mean difference, –0.35%; 95% CI, –0.48 to –0.23), according to researchers. There were no between-group differences for olive oil interventions vs. fish oil or polyunsaturated fatty acid-rich oils.
In sensitivity analyses, olive oil consumption was associated with improvements in HbA1c (mean difference, –0.28; 95% CI, –0.39 to –0.17) and fasting plasma glucose (mean difference, –0.34; 95% CI, –0.63 to –0.04) in trials with a low risk for bias.
“In light of other benefits, especially reported for extra virgin olive oil as an integral part of a Mediterranean diet, this vegetable oil represents a suitable component of a balanced diet,” the researcher wrote. – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.