Back in the 1970s, a myth took hold concerning the apparent heart-health benefits of traditional Mediterranean-region diets.
Population studies had revealed suggestive statistical associations between the relatively good heart health of rural Italians, Greeks, and Spaniards and—among other dietary patterns—their copious consumption of olive oil.
Scientists guessed that olive oil might be heart healthy because, unlike most vegetable oils, it’s high in omega-9 monounsaturated fatty acids (oleic acid) instead of omega-6 fatty acids.
But in truth, cheap, refined olive oil hasn’t been shown as particularly heart healthy… while olives and unrefined, extra virgin (EV) grade olive oil are virtually proven so.
Thanks to lab and clinical studies, it’s become clear that the cardiovascular health benefits of EV olive oil stem from its polyphenol-type antioxidants... not from the heart-neutral monounsaturated fatty acids that predominate in all grades of olive oil (See our sidebar, “Rare, potent polyphenols...”).
Among foods, certain uncommon polyphenol compounds—especially tyrosols and oleuropein—are virtually unique to olives and to EV (unrefined) olive oil.
To further confirm that polyphenols provide most of olive oil’s heart benefits, Spanish researchers conducted a small clinical trial (Vázquez-Velasco M et al. 2010).
They chose to test an olive polyphenol called hydroxytyrosol, because prior studies suggest that it may possess extraordinary vascular-health potential.
Volunteers were divided into two groups. One group received refined sunflower oil—which contains virtually no polyphenols. The second group received the same sunflower oil, but with added hydroxytyrosol.
As expected, the volunteers who consumed hydroxytyrosol-enriched sunflower oil showed greater antioxidant activity in their blood, as well as lower levels of oxidized LDL cholesterol and a marker of inflammation called soluble vascular cell adhesion molecule (sVCAM-1).
Oxidized LDL cholesterol is believed to be a major promoter of atherosclerosis—the buildup of fatty plaques in the arteries—and of cardiovascular disease in general.
Likewise, greater blood antioxidant capacity and lower blood levels of inflammation are associated with reduced cardiovascular risk.
Study underscores the unique health potential of extra virgin olive oil
For this study, researchers from the Universidad Complutense de Madrid recruited 22 healthy volunteers aged between 20 and 45 years, with body mass indices (BMIs) between 18 and 33 kg/m2… a range that encompasses low normal weight to obese.
For three weeks, the volunteers ate their normal diets, but also consumed either 10 to 15 grams per day of hydroxytyrosol-enriched sunflower oil—providing a daily hydroxytyrosol dose of 45mg to 50mg—or plain, non-enriched sunflower oil.
After the initial three weeks, the volunteers had two weeks of no additional oil (a so-called control phase) before “crossing over” to receive the other oil.
The results showed no changes in blood levels of total cholesterol, LDL cholesterol, or HDL (“good”) cholesterol in either group.
However, those taking the hydroxytyrosol-enriched sunflower oil enjoyed significant reductions in oxidized LDL cholesterol, which dropped from 79.8 units per liter (U/l) at the start of the study to 64.1 U/l after three weeks… compared with an increase from 72.7 to 86.4 U/l during the control (plain sunflower oil) phase.
Further, levels of arylesterase enzyme—a measure of the blood’s antioxidant capacity—increased from 235.2 to 448.9 U/l while participants were consuming the sunflower oil with added hydroxytyrosol, compared with a smaller increase from 204.1 to 310.3 U/l during the control (plain sunflower oil) phase.
The Spanish team drew this key conclusion:
“Although hydroxytyrosol-enriched sunflower oil was unable to reduce LDL-cholesterol or increase HDL-cholesterol, it acts as a functional food by increasing arylesterase activity and reducing oxidized LDL” (Vázquez-Velasco M et al. 2010).
The Spaniards’ results support the outcomes of similar clinical studies… and help paint a fuller picture, in which olives and extra virgin olive oil look better and better all the time.
- Vázquez-Velasco M, Esperanza Díaz L, Lucas R, Gómez-Martínez S, Bastida S, Marcos A, Sánchez-Muniz FJ. Effects of hydroxytyrosol-enriched sunflower oil consumption on CVD risk factors. Br J Nutr. 2010 Dec 8:1-5. [Epub ahead of print]