EASY ON THE OLIVE OIL?

Mediterranean diet claims under scrutiny. Why splashing out on olive oil may pay off.

It’s supposed to be good for you. So said a study published in 2013 that tracked the effects of the Mediterranean diet over five years, but its results have now been called into question.

The original research found that the diet – featuring fresh fruits and vegetables, seafood, nuts, olive oil and red wine, but very little red meat or sugar – reduced the risk of cardiovascular disease, contributed to slight reductions in rates of heart attack and early death, and more significantly lowered the risk of stroke.

Since then, study after study has found other benefits, such as staving off ageing in the brain or delaying the onset of Alzheimer’s disease.

But the 2013 study, known as PREDIMED, was recently retracted and republished (New England Journal of Medicine, doi.org/cq2s). That’s because not all of the study’s 7447 participants were fully randomised.

For instance, participants were assigned to follow either the low-fat control diet or one of two versions of the Mediterranean diet – with an emphasis on fats derived from either olive oil or walnuts. But some couples were both assigned to the same diet because of their marital status, so it wasn’t truly random.

The authors reanalysed their data, removing about 21 per cent of the participants. They found that the protective effects of the diet held up under this new scrutiny, but their scope was more limited: the health benefits were only seen for people with a high risk of heart disease.

Given these limited benefits, should we really all be eating like the Greeks? Another study suggests your bank balance is an important factor.

Researchers at the Mediterranean Neurological Institute in Italy carried out a study of more than 18,000 men and women over four years. They found a 15 per cent reduction in cardiovascular risk for those on the Mediterranean diet, but only if they earned £35,000 a year or more. For the less advantaged, the benefits of the diet weren’t seen at all.

Even though all study participants followed the Mediterranean diet, those with higher incomes tended to eat food that had more heart-protecting antioxidants and polyphenols, and which was grown with fewer pesticides. Those with lower incomes had less access to a wide variety of fruits, vegetables and whole grains, and tended to buy foods that had lower nutritional value (International Journal of Epidemiology, doi.org/cbhh).

“The real extra virgin olive oil that was used in the PREDIMED trial is about 8 euros per bottle,” says Marialaura Bonaccio at the Mediterranean Neurological Institute. “So the question is, do I get the same benefits from a bottle of olive oil that costs 10 euros, as compared to the lower quality one that I paid 2 euros for?”

She and her colleagues are planning a follow-up study to determine whether people are eating the quantities of food suggested by the Mediterranean diet, which will also look at the quality of those foods. She suspects that the difference in benefits may come down to higher quality foods that cost far more.

“It’s a real paradox. When the Mediterranean diet was discovered, it was the diet of the poorest people in Italy and Greece. Now, it’s the diet of the rich people,” she says.

Written by Chelsea Whyte in "New Scientist" UK, June 23-29, 2018, volume 238 issue 3183, excerpt p.25. Digitized, adapted and illustrated to be posted by Leopoldo Costa.