The Bitter Taste of Extra Virgin Olive Oil for a Sweet Long Life

Ramon Estruch, MD, PHD; Rosa M. Lamuela-Raventós, PHD; Emilio Ros, MD, PHD

Disclosures

J Am Coll Cardiol. 2020;75(15):1740-1742. 

Presently, unhealthy diets continue to be a critical contributor to cardiovascular disease, the main cause of death worldwide. According to the latest ranking of the best dietary patterns for health, the Mediterranean diet ranks first, followed by the DASH (Dietary Approaches to Stop Hypertension) and flexitarian (mostly vegetarian with occasional meat) diets.[1] The traditional Mediterranean diet is characterized by a high consumption of olive oil, nonrefined grains, vegetables, fruits, legumes, and nuts; a moderate consumption of seafood, poultry, and dairy products; a low consumption of meat and processed meat; and a moderate consumption of wine, always with meals.[2] Unrestricted use of olive oil in the kitchen and at the table is central to the traditional Mediterranean diet. Importantly, use of olive oil increases the palatability of salads and cooked vegetables, permitting the ingestion of higher quantities. Also, because the fat in olive oil is made mostly of monounsaturated fatty acids, which are more heat-stable than polyunsaturated fatty acids from seed oils, olive oil is the ideal culinary fat.[3]

Besides palatability and thermic stability, olive oil has a range of health benefits, but its quality is crucially important in this regard. Unlike most seed oils, which need to be refined to be edible, olive oil can be either refined or extra-virgin. Extra-virgin olive oil (EVOO) is obtained by cold pressing of ripe olives, and, in this sense, is a pure olive juice. As such, EVOO retains minor but highly bioactive hydrophilic components of olives, such as polyphenols, which are almost absent in common olive oil, a mixture of refined olive oil (usually >80%) and EVOO. Indeed, the type of olive oil has a major impact on human health. Thus, polyphenols in EVOO are believed to underlie many of the cardiometabolic benefits of olive oil consumption, among them, lower rates of cardiovascular disease (CVD) and diabetes, reduced low-density lipoprotein cholesterol and increased high-density lipoprotein (HDL) cholesterol, lower blood pressure, improved vascular reactivity, reduced inflammation, and enhanced HDL functionality.[4] Of note, as EVOO was used in 1 arm of the landmark PREDIMED (Prevención con Dieta Mediterránea) trial, wherein a 31% CVD risk reduction was obtained,[5] there is first-level scientific evidence on the cardioprotective properties of EVOO within the context of the Mediterranean diet.

Obviously, most information on the health benefits of olive oil has been collected in studies conducted in Mediterranean populations, and little is known of other geographical locations. In this issue of the Journal, Guasch-Ferré et al.[6] report findings from 3 seminal Harvard cohorts prospectively assessing olive oil consumption in relation to CVD that partly fill this gap. With nearly 93,000 study subjects and about 9,800 incident CVD cases after follow-up for 24 years, this large cohort study provides robust evidence of the association between olive oil consumption and incident CVD in a non-Mediterranean country, such as the United States. Results show that, compared with participants with the lowest olive oil consumption, those consuming >0.5 tablespoon/day of olive oil had a 14% lower risk of CVD and an 18% lower risk of coronary heart disease (CHD), thereby confirming findings of a recent meta-analysis.[7] However, contrary to the findings of this meta-analysis, Guasch-Ferré et al.[6] did not observe a lower risk of stroke with olive oil consumption. In a subset of participants, olive oil consumption was associated with raised HDL cholesterol and lower levels of circulating anti-inflammatory biomarkers, confirming prior observations.[4] Finally, in substitution analyses, replacing 5 g/day of margarine, butter, mayonnaise, or dairy fat with the equivalent amount of olive oil was associated with 5% to 7% lower risk of CVD and CHD. No significant associations were observed when olive oil was compared with other vegetable oils.

Some aspects of this study merit consideration. First, the results concern total olive oil, as no information on the type of olive oil consumed was available. Part of the salutary health effects of olive oil are due to its content in oleic acid, which is found in all types of olive oil, but an important part is attributable to the >200 minor components that include mainly phenolic compounds, but also tocopherols, phytosterols, carotenoids, luteolin, and triterpenic acids, which are enriched in EVOO.[4] Most prospective studies relating exposure to olive oil to CVD do not distinguish between olive oil types, with 2 exceptions. In the Spanish cohort of the EPIC (European Prospective Investigation into Cancer and Nutrition) study,[8] a 14% decrease in CHD risk was observed for each 10 g/day per 2,000-kcal increment in EVOO, whereas consumption of common olive oil disclosed no association. Similarly, in the PREDIMED study, considered as an observational cohort,[9] total CVD was significantly decreased by 10% for each 10 g/day increase in EVOO, but common olive oil was unrelated.

Second, in the present study, the mean consumption of olive oil was only 12 g/day in the highest category (5% of the overall cohort), and barely 10% of participants consumed >1 teaspoon (4.5 g) daily. These are very low values compared to the usual consumption in Mediterranean areas. In the PREDIMED trial, mean baseline olive oil consumption was 38 g/day,[5] a value that more than triples that of the highest category of consumption in the U.S. cohort. Such marginal olive oil consumption in the Harvard cohorts and ensuing low statistical power may explain the nonsignificant association with stroke (hazard ratio: 0.96 [95% confidence interval: 0.92 to 1.01] per each 5 g/day increase), which contrasts with findings of other prospective studies.[7]

Third, olive oil consumption was determined from dietary questionnaires, which are subject to bias and misreporting. One way to circumvent this problem is to measure objective biomarkers of consumption, such as urinary hydroxytyrosol, the main polyphenol metabolite in olive oil, as was done in the PREDIMED trial.[5] In this way, a dose-response according to hydroxytyrosol levels can be assessed that may help to determine a causal relationship between olive oil consumption and clinical outcomes.

Finally, the findings of the present study also suggest that the replacement of more saturated fats, such as butter, margarine, mayonnaise, and dairy fat, with olive oil entails a lower CVD risk. This is a further argument for promoting the use of olive oil in place of less healthy fats in the U.S. population.

A final consideration on the quality of the phenol profile in EVOO is needed. Some of the EVOO polyphenols are unique, both because they are exclusively present in this food and for their sensory properties, since they have a very distinctive bitter and pungent taste, among them oleacein and oleocanthal, 2 secoiridoids that are not present originally in olives, but are naturally formed during the production of EVOO. Together with the hydroxytyrosol found in urine after the consumption of EVOO, these molecules are gaining attention for their anti-inflammatory properties.[10] Other interesting bioactive compounds are oleuropein, another polyphenol, and some triterpenes, such as squalene and oleanolic and maslinic acids. In fact, ongoing feeding trials are evaluating the effects of functional olive oils (EVOO enriched with these compounds) to increase the antioxidant and anti-inflammatory effects of the original EVOO.[11] Regardless, further research is warranted to demonstrate the exclusive effects of different doses of different types of EVOO (depending on olive ripeness, cultivar, climate, and extraction processes) on relevant clinical outcomes. Because randomized intervention studies based on hard clinical endpoints are difficult, expensive, and time-consuming, easier and more feasible strategies could be used, for instance, the evaluation of the effects of different EVOOs on atherosclerotic burden measured by noninvasive imaging techniques, as done in a PREDIMED substudy.[12]

In conclusion, olive oil, a key food of the Mediterranean diet, is scarcely used by well-educated U.S. cohorts such as those of the present study, but even so, its use is associated with lower CVD rates in them. EVOO, the bitter tasting but more beneficial type of olive oil, could be included in other healthy diets (i.e., DASH diet, flexitarian diet, and other plant-based diets) to promote CVD prevention. New virgin olive oils with a better profile of bioactive compounds may help upgrade the health benefits of olive oil.

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