A recent analysis from the Harvard health studies
By Dr Malcolm Mackay
A recently published study found that olive oil and other vegetable oils were equally effective in reducing mortality but more effective than other fats. However, the results have been widely misrepresented as evidence for health benefits that are unique to olive oil, even among health professionals who would usually discourage the consumption of energy dense, nutrient poor food products.
The study analysed total and disease specific mortality data from the Nurses’ Health Study and the Health Professionals Follow-up Study (1990-2018). The quantity of olive oil consumed by subjects in this study was quite small, averaging only 9g per day (half an Australian tablespoon) in the high olive oil intake group.
The introduction section of the paper conflates a Mediterranean diet with olive oil consumption – a common oversight in discussions of the healthfulness or otherwise of olive oil. The conflation continued in the discussion section of the paper in reference to the PREDIMED study, olive oil and breast cancer risk. A Mediterranean diet is characterised by limited quantities of meat and processed foods, high intakes of whole plant foods, and some olive oil and fish. It’s a healthier overall dietary pattern, not just an olive oil-rich diet.
The study found a statistically significant reduction in all-cause mortality and four categories of disease specific mortality in subjects who used olive oil. When we see observational data like this, we ask ourselves, “what other healthy habits might the item be associated with”? The statistical analysis adjusted the data to try and account for the observation that the olive oil using subjects had healthier diet and lifestyle behaviours. The other question we ask ourselves is, “healthier, compared to what”? The subjects in this study were on the standard American diet (SAD), mostly comprising animal products and processed foods. Almost any food would look good beside this.
The study contained an infographic of the potential mechanisms by which olive oil might improve cardiovascular and other health outcomes. The chart included phytochemicals and physiological mechanisms specific to high quality, extra virgin olive oil. We consider that the placement of this prominent infographic in the publication was misleading. The study did not demonstrate a health benefit specific to extra virgin olive oil. The dietary data collected did not specify the type of olive oil consumed. (The majority of commercial olive oil is not particularly high in polyphenols). Moreover, the study found no significant difference in all-cause or disease specific mortality between olive oil and other unsaturated vegetable oils.
The key figure in the publication was a forest chart of mortality ratios comparing olive oil to five groups of fats – margarine, butter, mayonnaise, other vegetable oils, and dairy fat. Olive oil was significantly better (less mortality) across all disease groups compared to margarine, butter, mayonnaise, and dairy fats. However, olive oil was no better than ‘other vegetable oils’ for total mortality or any category of disease specific mortality.
The authors of the study concluded that, “Our results support current dietary recommendations to increase the intake of olive oil and other unsaturated vegetable oils in place of other fats to improve overall health and longevity”. This is clearly a recommendation to replace worse fats with less bad fats. It was not a recommendation to eat more olive oil.
A whole foods, plant-based diet contains none of the ‘other fats’ for which olive oil would be a better choice. The fats naturally present in our diet are predominantly unsaturated, rich in essential fatty acids, and retain the fibre, nutrients and protective phytochemicals found only in whole plant foods. The addition of olive oil to our meals would add extra calories without any additional nutrients or fibre. The result would be either weight gain, reduced nutrient intake, or a combination of both.
This study is one of many published in recent years that claim to demonstrate the health benefits of olive oil. Most of the recent research on olive oil is funded by industry. We are aware of research dating back many decades that shows the detrimental effects of oil, including olive oil, on artery function and lipid metabolism. The recent olive oil industry funded studies have not overturned these older findings, rather they have ignored them.
See our No Oil! page for a full explanation of why we recommend avoiding this calorie rich and nutrient poor food.
Study:
Guasch-Ferré, M., Li, Y., Willett, W. C., Sun, Q., Sampson, L., Salas-Salvadó, J., . . . Hu, F. B. (2022). Consumption of Olive Oil and Risk of Total and Cause-Specific Mortality Among U.S. Adults. Journal of the American College of Cardiology, 79(2), 101-112 (not available on open access)
Page created 28 March 2022
Page last updated 28 March 2022