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Scientists behind the study examined how the long-term consumption of different dietary fat sources such as olive, sunflower and fish oils affects the liver of rats. As part of the comprehensive study, the researchers carried out a complete analysis of the liver genome, aiming to establish how it evolved in line with a rat's consumption of different oils.
They looked at three types of oil: virgin olive oil, sunflower oil and fish oils. According to their findings, virgin olive oil proved to be the best at preserving the liver.
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Fish oil, on the other hand, increased oxidation of the liver associated with aging, reduced mitochondrial electron transport chain activity and changed the relative length of telomeres (chromosomes whose length can affect aging in cells and cause cancer).
Sunflower oil was also demonstrated to cause negative effects.
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"The alterations caused by the long-term consumption of sunflower and fish oils make the liver susceptible to NASH," Morales told The Daily Mail. He also warned that NASH is a "very serious disease that may act as a catalyst for other liver diseases such as cirrhosis and liver cancer."
Although many nutritionists have classified fish oil as a super food and it has been previously linked to health benefits, this isn't the first time scientists have suggested it may not be so great.
Previous research has suggested taking fish oil supplements can lower the risk of death from heart disease, while others have found no benefit. A recently published review of data from 10 studies involving a total of nearly 78,000 people, revealed that patients regularly taking fish oil supplements were just as likely to experience a stroke or heart attack within a four year period of time as those who did not, according to Live Science.
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Dr. Howard LeWine, chief medical editor at Harvard Health Publishing, wrote in a 2013 blog post that he believes the evidence for fish oils' benefits and risks will be a topic of debate for the foreseeable future.
"Experts will surely remain divided on their opinions about fish oil supplements for the general population. And don't expect any clarity about what to do any time soon. I expect other studies with flip-flopping results in the future," he wrote.
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For now, Morales suggests those concerned for their liver stick to consuming virgin olive oil instead of the other alternatives.
"Virgin olive oil is the healthiest option," the researcher said, explaining that it "has already been proven in relation to diverse aspects of health."