Summary
Olive oil is known for its polyphenols—plant compounds that act as antioxidants in test-tube studies. But do these antioxidants actually work inside the human body? This study set out to answer that question by testing how different levels of olive-oil polyphenols affect oxidative stress after eating a high-fat meal.
Twelve healthy men participated in a crossover trial where each of them consumed 40 mL of olive oil on three separate occasions. The oils were almost identical except for their phenolic content: one was high, one moderate, and one very low. Before each test, participants followed a strict low-antioxidant diet to “clear the slate,” making it easier to detect the effects of the oils themselves.
The findings were clear and dose-dependent. The more polyphenols the olive oil contained, the more of these compounds—especially tyrosol and hydroxytyrosol—appeared in the bloodstream. These same compounds were also incorporated into LDL particles (“bad cholesterol”), effectively enriching them with antioxidants.
Interestingly, ingesting 40 mL of olive oil by itself does create a temporary rise in oxidative stress. But the extent of this stress depended heavily on the oil’s polyphenol content. Oils rich in polyphenols significantly reduced LDL oxidation, meaning they offered better protection against the oxidative effects of the meal.
In simple terms, this study shows that olive-oil polyphenols don’t just sit in the bottle—they’re absorbed, used by the body, and help defend LDL particles against oxidation after eating. The higher the polyphenol content of the olive oil, the stronger the protective effect.
PMID: 16458191
DOI: 10.1016/j.freeradbiomed.2005.09.027
Abstract
Olive oil phenolic compounds are potent antioxidants in vitro, but evidence for antioxidant action in vivo is controversial. We examined the role of the phenolic compounds from olive oil on postprandial oxidative stress and LDL antioxidant content. Oral fat loads of 40 mL of similar olive oils, but with high (366 mg/kg), moderate (164 mg/kg), and low (2.7 mg/kg) phenolic content, were administered to 12 healthy male volunteers in a cross-over study design after a washout period in which a strict antioxidant diet was followed. Tyrosol and hydroxytyrosol, phenolic compounds of olive oil, were dose-dependently absorbed (p<0.001). Total phenolic compounds in LDL increased at postprandial state in a direct relationship with the phenolic compounds content of the olive oil ingested (p<0.05). Plasma concentrations of tyrosol, hydroxytyrosol, and 3-O-methyl-hydroxytyrosol directly correlated with changes in the total phenolic compounds content of the LDL after the high phenolic compounds content olive oil ingestion. A 40 mL dose of olive oil promoted a postprandial oxidative stress, the degree of LDL oxidation being lower as the phenolic content of the olive oil administered increases. In conclusion, olive oil phenolic content seems to modulate the LDL phenolic content and the postprandial oxidative stress promoted by 40 mL olive oil ingestion in humans.
Covas MI, de la Torre K, Farré-Albaladejo M, Kaikkonen J, Fitó M, López-Sabater C, Pujadas-Bastardes MA, Joglar J, Weinbrenner T, Lamuela-Raventós RM, de la Torre R. Postprandial LDL phenolic content and LDL oxidation are modulated by olive oil phenolic compounds in humans. Free Radic Biol Med. 2006 Feb 15;40(4):608-16. doi: 10.1016/j.freeradbiomed.2005.09.027. Epub 2005 Oct 18. PMID: 16458191.