A new mouse study suggests that extra-virgin olive oil can reverse the signs of nonalcoholic fatty liver disease.
Previous research has shown that olive oil - and especially extra-virgin olive oil - may reduce the risk of cardiovascular disease. However, not much is known about the mechanisms responsible for this association between olive oil consumption and cardiovascular health benefits.
This is why a team of researchers - led by Dr. Rodrigo Valenzuela from the University of Chile in South America - set out to investigate the effects of a compound found in extra-virgin olive oil on the health of mice.
The compound is called hydroxytyrosol and, as the scientists explain, it is a polyphenol with well-known antioxidant properties. These properties have been suspected to be the reason behind the many health benefits of olive oil.
This new research, however, shows that hydroxytyrosol also has a protective effect on the liver. The findings were published in the journal Lipids in Health and Disease.
Analyzing the effect of hydroxytyrosol on mice
Dr. Valenzuela and colleagues examined the effects of hydroxytyrosol on mice that were fed a diet high in fats.
Specifically, they looked at certain enzymes that play a key role in the synthesis of some polyunsaturated fatty acids. Polyunsaturated fats are beneficial to one's health because they can lower "bad" cholesterol levels, improve cardiovascular health, brain function, and cell growth.
The so-called bad cholesterol is also known as low-density lipoprotein (LDL) cholesterol. It is referred to as the "bad" cholesterol because it is the kind of fat that can build up inside the arteries, hardening or blocking them over time and contributing to a number of cardiovascular diseases.
By contrast, high-density lipoprotein (HDL) cholesterol is known as the "good" cholesterol because it transports the cholesterol from other parts of the human body back to the liver, where it is processed and eliminated.
The researchers fed four groups of mice, each comprising 12 to 14 rodents, either a high-fat diet (consisting of 60 percent fat) or a control diet (with only 10 percent fat). Additionally, some mice were also administered 5 milligrams of hydroxytyrosol per kilogram of body weight over a period of 12 weeks.
Dr. Valenzuela and team took blood and tissue samples from the mice at the end of the experiment. They analyzed the effects of the diet on the composition of fatty acids, the activity of the enzymes considered, and on oxidative stress.
Hydroxytyrosol reverses signs of fatty liver disease
In the mice that had been fed a high-fat diet, both the total cholesterol levels and the levels of LDL-cholesterol increased, while the HDL cholesterol remained unchanged. However, hydroxytyrosol seemed to reduce the negative effect of these types of cholesterol in the mice that had taken it.
A high-fat diet also seemed to raise the markers of insulin resistance. Again, in the mice that had also taken hydroxytyrosol, these markers were reduced. However, they were not as low as the levels of the mice that had been on a regular diet.
Importantly, mice that had been on a high-fat diet showed decreased levels of the liver enzymes that help to synthesize the beneficial polyunsaturated fatty acids. The reduction in the liver enzymes was connected with an imbalance in the fatty acids found in the liver, brain, and heart.
However, the mice whose high-fat diet was also supplemented with hydroxytyrosol showed enzymatic activity and fatty acid composition similar to that of the mice that were fed a normal diet. This suggests that hydroxytyrosol may have reversed the damaging effects of a high-fat diet.
Dr. Valenzuela explains the results:
"Our results indicate that hydroxytyrosol may be a key part of the health benefits of extra-virgin olive oil.
Mice fed on a high-fat diet had signs of nonalcoholic liver disease which we believe has led to the noticeable reduction in enzyme activity in the liver and the negative effects on fatty acid composition in this, and other, organs. We also found that the liver showed signs of increased oxidative stress, which we know has links to fatty liver disease. It is intriguing that adding a relatively low dose of hydroxytyrosol to the diet was able to reverse these effects, reduce the signs of fatty liver disease, and reduce negative effects seen in the other organs."