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, 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.
Dietary extra-virgin olive oil rich in phenolic antioxidants and the aging process: long-term effects in the rat.
The aim of the present work was to verify whether extra-virgin olive oil, a food naturally containing phenolic antioxidants, has the potential to protect from the pro-aging effects of a high-calorie diet. Male rats were fed from age 12 months to senescence a high-calorie diet containing either corn oil (CO), or extra-virgin olive oil with high (H-EVOO) or low (L-EVOO) amounts of phenols. The prolonged high fat intake led to obesity, liver lipid degeneration and insulin resistance, which were not counteracted by high phenol intake. No difference in overall survival was found at the end of the experiment in the animals treated with H-EVOO compared to the other groups. However, we did detect a protective effect of olive oil on some age-related pathologies and on blood pressure, of which the former was associated with the antioxidant content. Concomitantly, a decrease in DNA oxidative damage in blood cells and plasma TBARS and an increase in liver superoxide dismutase were detected following H-EVOO consumption. Thus, although olive oil phenols cannot reverse the detrimental effects of a prolonged intake of high amounts of fat, improving the quality of olive oil in terms of antioxidant content can be beneficial.
PMID: 19369055 [PubMed – indexed for MEDLINE]