Extra virgin olive oil is one of the best-studied foods in nutrition research, central to the Mediterranean diet. A newer category, "high-phenolic" or "high-polyphenol" oil, is sold at two to three times the price of ordinary extra virgin. Here is what the number on the label means.
What polyphenols are
Polyphenols are compounds the olive makes to protect itself, including hydroxytyrosol, tyrosol, oleocanthal and oleacein. They give good oil its bitterness and the peppery catch at the back of the throat. Their amount depends on the olive variety, how early the fruit was picked, how it was milled, and how the oil has been stored since.
The one authorized claim
In the European Union, olive oil is allowed one specific health claim: "olive oil polyphenols contribute to the protection of blood lipids from oxidative stress." It may be used only for oil containing at least 5 mg of hydroxytyrosol and its derivatives per 20 g of oil (about 250 mg per kilogram), with the effect linked to a daily intake of 20 g. That threshold is the most useful benchmark a shopper has.
Reading the number
- Units. Results are usually given in mg per kg. Around 250 mg/kg meets the EU claim threshold; oils sold as high-phenolic often state 500 to over 1,000 mg/kg.
- Method. Labs use different methods (HPLC methods, NMR). Results from different methods are not directly comparable, so compare oils tested the same way.
- Date. Polyphenols decline over time. A lab report from right after milling describes a fresher oil than the one in your kitchen months later. Look for the harvest date and the test date.
Keeping it
Light, heat and air break polyphenols down. Buy oil in dark glass or tin, keep it closed and away from the stove, and use it within a few months of opening. Use the best oil raw, on food, where you can taste it.
Sources
- Commission Regulation (EU) No 432/2012, list of permitted health claims.
- EFSA, Scientific Opinion on the substantiation of health claims related to polyphenols in olive, 2011.
This guide is general information, not medical advice. Talk to your doctor or pharmacist before starting a supplement if you are pregnant or nursing, take medication, or have a medical condition.