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22.05.2009


Life-extending effect of virgin olive oil shown in fat rats

Westerners are getting fatter and fatter. If they were to get most of their dietary fat from cold-pressed olive oil they might not lose weight, but they’d probably be healthier. Italian researchers at the University of Florence come to this conclusion in an animal study soon to be published in the Journal of Nutritional Biochemistry.

The researchers gave one-year-old adult male rats a diet resembling that of Westerners who overeat. The rats were kept on the diet, in which over forty percent of the energy came from fat, for a year. The researchers mixed the rat feed with corn oil [CO], virgin olive oil with a high level of phenols, similar to commercially available olive oil [H-EVOO], or olive oil from which the phenols had been removed [L-EVOO].


Corn oil contains predominantly polyunsaturated n-6 fatty acids. Olive oil contains mostly monounsaturated fatty acids. Olive oil also contains a high amount of tyrosine metabolites. These phenols have a health promoting effect, and are found above all in extra-virgin olive oil. The table below shows the comparative amounts of phenols in the virgin olive oil and the refined oil that the researchers made themselves.



By the end of the experiment the rats were two years old, and had reached old age in lab-rat terms. Ordinary rats live longer, but lab rats have a shorter life expectancy because of inbreeding. Some animals died during the experiment and some became so ill that they were killed. The animals became fatter, and post mortems revealed that many of them had a fatty liver, in particular the rats that had been given olive oil. On the other hand, the virgin olive oil protected against tumours. The animals that were given extra virgin olive oil during the experiment were least likely to die.



The researchers measured the amount of damage to the genetic material in the rats’ blood cells. The damage was less in the rats that had had the extra-virgin olive oil diet. These rats had lower levels of TBARS, a marker for damage caused by free radicals.



The blood pressure of the rats on the corn oil diet rose. In the olive-oil rats their blood pressure remained stable.

For health freaks this research provides an argument for replacing ordinary olive oil with extra-virgin olive oil. But these people probably don’t overeat, so it’s not clear to what extent extra-virgin olive oil would have a health-enhancing effect. The researchers are cautious: "Improving the quality of olive oil in terms of antioxidant content can have some beneficial effects, but it is not sufficient by itself to counteract the detrimental effects of a high-calorie diet containing large amounts of fat", they conclude in the article. "Future experiments will elucidate whether the protective effects of olive oil phenols on age-related dysfunctions would be more evident using a lower-calorie and lipid intake regimen."

The researchers received EU financing from the FLAVO 2005-513960 programme and the Network of Excellence in Nutrigenomics, NuGO FOOD-CT-2004-506360. Two years ago Professor Martijn Katan expressed his scepticism in the Dutch national press about the positive health effects reported in EU studies on olive oil. [Trouw 18 januari 2007] “Olive oil is healthy”, Katan said in the interview. “But it’s no healthier than other vegetable oil. But Europe has an olive oil lake. That’s why the EU has financed so much research into the usefulness of olive oil. Thanks to all the advertising associated with this, olive oil now has the reputation of being most healthy, but this is not the case.”

Source:
J Nutr Biochem. 2009 Apr 13. [Epub ahead of print].

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