Summary
Olive oil contains natural polyphenols that act as antioxidants in the lab, but the big question has always been whether these benefits actually show up inside the human body. This study set out to test that directly by comparing olive oils with different levels of polyphenols.
Thirty healthy volunteers took part in a carefully designed, double-blind, randomized crossover trial. Each person consumed three types of olive oil—low, medium, and high in phenolic compounds—for three weeks at a time, with washout periods in between. Because each participant tried all three oils, the researchers could clearly see how the phenolic content affected the body.
What they found strongly supports the antioxidant power of polyphenols in everyday life. As the phenolic content of the olive oil increased, levels of tyrosol and hydroxytyrosol—two key olive-oil phenols—also increased in the participants’ urine, showing that the body was absorbing and processing these compounds. More importantly, oxidized LDL levels went down, and LDL particles became more resistant to oxidation. Both changes represent real, measurable protection against processes linked to heart disease.
Another encouraging finding was a modest rise in HDL cholesterol (“good cholesterol”) after people consumed virgin olive oil with the highest phenolic content.
Overall, the results paint a clear picture: regularly consuming virgin olive oil rich in polyphenols can help reduce oxidative stress, protect LDL from oxidation, and even support healthier cholesterol levels. The higher the phenolic content, the stronger the benefits—suggesting that choosing high-quality, polyphenol-rich olive oil may offer meaningful protection against oxidative damage in the body.
PMID: 15168036
DOI: 10.1007/s00394-004-0452-8
Abstract
Background: Evidence from in vitro studies suggests that antioxidant olive oil phenolic compounds can prevent LDL oxidation. However, in vivo evidence in support of this hypothesis is sparse.
Aim of the study: to establish the antioxidant effect of olive oils with differences in their phenolic compounds content in humans
Methods: A controlled, double blind, cross-over, randomized, clinical trial using three similar olive oils with increasing phenolic concentration (from 0 to 150 mg/Kg) was conducted in 30 healthy volunteers. Olive oils were administered over three periods of 3 weeks preceded by two-week washout periods.
Results: Urinary tyrosol and hydroxytyrosol increased (p < 0.020), in vivo plasma oxidized LDL decreased (p = 0.006), and ex vivo resistance of LDL to oxidation increased (p = 0.012) with the phenolic content of the olive oil administered. After virgin olive oil administration, an increase (p = 0.029) was observed in HDL cholesterol levels.
Conclusions: Sustained consumption of virgin olive oil with the high phenolic content was more effective in protecting LDL from oxidation and in rising HDL cholesterol levels than that of other type of olive oils. Dose-dependent changes in oxidative stress markers, and phenolic compounds in urine, were observed with the phenolic content of the olive oil administered. Our results support the hypothesis that virgin olive oil consumption could provide benefits in the prevention of oxidative processes.
Marrugat J, Covas MI, Fitó M, Schröder H, Miró-Casas E, Gimeno E, López-Sabater MC, de la Torre R, Farré M; SOLOS Investigators. Effects of differing phenolic content in dietary olive oils on lipids and LDL oxidation--a randomized controlled trial. Eur J Nutr. 2004 Jun;43(3):140-7. doi: 10.1007/s00394-004-0452-8. Epub 2004 Jan 6. PMID: 15168036.