What it is

Olive oil is the fat pressed from olives; most of its fatty acids have one double bond, and virgin oils contain small amounts of phenolic compounds 12.

Per 100 g, extra virgin olive oil contains on average 67.8 g cis-18:1 fatty acids, 15.4 g saturated fatty acids and 8.4 g linoleic acid 1. Its main phenolic compounds are the dialdehydes of oleuropein aglycone, mean 25.16 mg per 100 g (range 0.08 to 94.20), and of ligstroside aglycone, 14.28 mg, against 0.77 mg of free hydroxytyrosol 2.

In the body

Human cells make oleic acid from a saturated fatty acid, and the gut probably absorbs more than half of olive oil’s phenolic compounds 34.

Stearoyl-CoA desaturase (SCD) forms oleoyl-CoA by inserting a cis Δ9 double bond into stearoyl-CoA, with O2 and electrons from reduced cytochrome b5 3.

Synthesis of oleic acidCytosol, then endoplasmic reticulum membrane
  1. Acetyl-CoA
  2. Acetyl-CoA carboxylase 1 (ACACA)ATP, HCO3−, BiotinFirst and rate-limiting step of de novo fatty acid synthesis
  3. Malonyl-CoA
  4. Fatty acid synthase (FASN)Acetyl-CoA, 14 NADPH7 malonyl-CoA per palmitate; releases 7 CO2; thioesterase domain frees 16:0
  5. Palmitate (16:0)
  6. Long-chain-fatty-acid–CoA ligases (ACSL)ATP, CoA, Mg2+Releases AMP and diphosphate
  7. Palmitoyl-CoA
  8. several stepsMalonyl-CoA, 2 NADPHElongation cycle: ELOVL6, HSD17B12, HACD, TECR; releases CO2
  9. Stearoyl-CoA (18:0)
  10. Stearoyl-CoA desaturase (SCD)O2, 2 reduced cytochrome b5NADH-cytochrome b5 reductase (CYB5R3) supplies the electrons
  11. Oleoyl-CoA (18:1 cis-Δ9)

Absorbed tyrosol and hydroxytyrosol enter lipoprotein fractions, and hydroxytyrosol is excreted in urine as a glucuronide 4.

What studies show

In a Spanish trial, a Mediterranean diet with extra virgin olive oil was followed by fewer heart attacks, strokes and cardiovascular deaths than low-fat advice 5.

PREDIMED assigned 7447 adults at high cardiovascular risk to a Mediterranean diet with extra virgin olive oil, 1 litre a week per household, a Mediterranean diet with nuts, or advice to reduce dietary fat 5. Over a median 4.8 years, myocardial infarction, stroke or cardiovascular death occurred in 96 of 2543 participants on the olive oil diet and 109 of 2450 controls 5. The 5-year risks were 3.6% and 5.7% (adjusted hazard ratio 0.69, 95% CI 0.53 to 0.91), a number needed to treat of 48 for 5 years 5. Deaths from any cause numbered 118 and 114 (hazard ratio 0.90, 0.69 to 1.18) 5.

The 2013 report was withdrawn after deviations from randomisation emerged, including 425 household members and 467 participants at one site who were not randomised individually 5. After exclusion of 1588 participants with known or suspected deviations, the olive oil hazard ratio was 0.71 (0.52 to 0.97) 5. Public bodies, chiefly Spain’s Instituto de Salud Carlos III, and the Fundación Mapfre funded the trial 5. Olive oil and nut firms and trade bodies donated the foods; sponsors had no role in design, analysis or reporting 5.