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Olive oil is often said to be "healthy".

This study, for example, states:

For each 10 g/d increase in extra-virgin olive oil consumption, cardiovascular disease and mortality risk decreased by 10% and 7%, respectively. No significant associations were found for cancer and all-cause mortality.

It's unclear if such claims are talking about olive oil as a replacement for other dietary fats, or as an addition. Are such studies controlling other factors (like olive oil being chosen by wealthier health-conscious people)?

Also, in the above study, why aren't they seeing an association with all-cause mortality? Should we assume that olive oil lowered cardiovascular mortality, but increased other mortality?

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  • All-cause mortality is a term used by epidemiologists, or disease-tracking scientists, to refer to statistical cause of death from any cause. Not just cardiovascular disease. – Chris Rogers Aug 18 '19 at 7:37
  • @ChrisRogers I understand that (But I don't understand the purpose of your comment) – user10901 Aug 18 '19 at 7:53
  • You asked if seeing no significant associations with all-cause mortality could mean that olive oil could increase other causes. It means there is no significant increase or reduction in mortality overall. – Chris Rogers Aug 18 '19 at 8:05
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    There are two questions here, and the one in the paragraph with the bold text is one your own research should have answered. One would have to read the full study to see what they're controlling for. As for the second question, I think that's just a result of a poorly written paragraph. (It's very likely translated from Spanish.) I'm quite confident that if olive oil increased mortality in any category other studies would have revealed that by now. – Carey Gregory♦ Aug 18 '19 at 22:07
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    Haven't looked at the study but be wary of interpreting "no significant" as "no difference" - they are not the same thing. – Bryan Krause Aug 18 '19 at 22:33
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Olive oil contains mainly monounsaturated fat made of oleic acid.

The current evidence suggests that unsaturated fat may be beneficial as replacement for saturated fat, that is by increasing unsaturated/saturated fat ratio. Most of the evidence suggest that polyunsaturated fat may be more benefical for the heart health than monounsaturated fat (Health.gov 2015, Cochrane 2015, Annual Reviews in Nutrition 2016, NMCD 2017).

There is some weak association between olive oil and reduced risk of heart disease, but the included studies could not isolate the effect from other foods consumed:

Researchers in PREDIMED study have found statistically significant association between olive oil consumption and cardiovascular mortality, but when checked for all-cause mortality, the association was no longer statistically significant.

In one meta-analyses, they concluded that olive oil may contribute to benefits of Mediterranean diet, but it's not possible to say if olive oil as such, or only as a source of unsaturated fat, is beneficial (Frontiers in Nutrition 2019). Anyway, a recent systematic review did not bring a clear conclusion about benefits of Mediterranean diet for heart health (Cochrane 2019).

In a recent systematic review, sunflower oil, was associated with lower LDL cholesterol levels than olive oil (Journal of Lipid Research 2018).

In conclusion, currently there is no clear evidence to say that olive oil as such is beneficial for heart, but it could be beneficial as one of the sources of unsaturated fat when replaced for saturated fat.

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  • They didn't ask the participants about their other habits (health-conscious people make healthy choices, like avoiding alcohol and smoking), or about their consumption of saturated fats? (If so, I think it's safe to say that the study is worthless. They should have done a multi-variate linear regression, etc.) – user10901 Aug 19 '19 at 19:30
  • @MaxB, in the full version of the article, it is said that the participants included were all Mediterraneans, 55-80 years old with no evidence of cardiovascular disease, but had at least one risk factor for it: smoking, high blood pressure, diabetes, obesity, family history, etc. They excluded everyone with BMI >40 or any chronic disease, alcohol or drug abuse. The major problem with this study is its short duration (5 years) and the fact that it was just observational and without clear information of the overall diets participants had. – Jan Aug 20 '19 at 6:44
  • Taking the info from other studies together, the evidence about health benefits of olive oil is weak. – Jan Aug 20 '19 at 6:45

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