[ROTMetro]

Quoting DoingIsLearning from these comments:

The study was in Spain were both the quality of olive oil is very high and the retail cost fairly low comparatively with the rest if the world. Also many arguably poor farmers will grow their own olive trees and distribute the oil yield among their wider family.

So perhaps not so case closed as you say.

[Matthewiiv]

That's a fair point, although I would argue that if good quality olive oil is very cheap, then perhaps it's the other way round. Only the very poorest are forced to consume non extra virgin olive oil.

Also, I'm not sure about Spain but farmers generally have noticeably higher life expectancy than the average.