Extra virgin olive oil consumption had a positive impact on two comorbidities of non-alcoholic fatty liver disease – obesity and diabetes – in mice, according to the results of a recent study.
However, researchers also found that excessive intake of extra virgin olive oil in a high-fat diet caused the same liver damage as a diet high in saturated fats.
To our surprise, the extra virgin olive oil intake did not improve the liver damage caused by high-fat diets. However, extra virgin olive oil intake was able to improve body weight and insulin resistance.
The study, which was published in Nature, investigated the impact of different types of high-fat diets and one low-fat diet on non-alcoholic fatty liver disease, a condition often derived from obesity and associated with insulin resistance.
The presence of non-alcoholic fatty liver disease is correlated with a higher risk of stroke, diabetes and heart disease.See Also: Grant Recipient to Study Impacts of Polyphenols on DNA Function
“Our study was designed to explore the mechanisms of the positive effects of extra virgin olive oil intake,” Franz Martín and Robert Kleemann, two authors of the study, told Olive Oil Times.
“What we did was analyze extra virgin olive oil composition, mainly sterols and phenols, and then explore the effects of extra virgin olive oil high-fat diets on the traits related to non-alcoholic fatty liver disease and type 2 diabetes,” the researchers added, referring to traits such as body weight, plasma lipid profile, glucose homeostasis, insulin sensitivity and histology markers of liver damage.
The research examined the effects of high-fat diets based on lard, extra virgin olive oil and extra virgin olive oil enriched with polyphenols against the effects of a low-fat diet.
“To our surprise, the extra virgin olive oil intake did not improve the liver damage caused by high-fat diets,” the two researchers said. “Thus, in the case of high-fat diets based on extra virgin olive oils, there were no relevant differences in liver damage when compared with saturated fats in high-fat diets.”
“However, extra virgin olive oil intake was able to improve body weight and insulin resistance,” they added.
According to the researchers, the study shows that excessive consumption of healthy oils over long periods may damage the liver because those oils accumulate in the cells.
“In the beginning, healthy oils can reduce inflammation, but if you accumulate high amounts of ‘good’ fatty acids in a cell, this cell will become dysfunctional because all cellular processes are hampered due to the sheer physical overload with lipids,” Martín and Kleemann said.
In other words, explained the researchers, “if one eats too much, even from healthy products, they may undergo adverse long-term effects.”
“It is extremely important to activate metabolism with exercise so that the beneficial lipids consumed are processed and utilized by the body,” Martín and Kleemann added. “Then, the real health effects of unsaturated lipids may have a much greater role because, if they are stored in vesicles as triglycerides, they cannot exert bioactive health effects.”
The study also demonstrated how the level of polyphenols present in the two types of extra virgin olive oil high-fat diets did not have much impact on the outcome.See Also: Tips for Selecting High-Polyphenol Olive Oils
“We saw that the intake of an extra virgin olive oil that was much richer in polyphenols did not add any difference,” Martín and Kleemann said. “The effect was similar to the other extra virgin olive oil.”
“The reason could be that extra virgin olive oil already contains sufficient levels of polyphenols and more polyphenols do not add anything,” they added. “Thus, sometimes more is not better.”
The researchers concluded that neither a low-fat diet nor an extra virgin olive oil-based high-fat diet was better at preventing non-alcoholic fatty liver disease.
“However, all the evidence suggests that the best way to prevent non-alcoholic fatty liver disease is a normal-caloric healthy and varied diet, together with physical activity,” Martín and Kleemann said. “To date, there is no other way.”
“Concerning the issue of insulin resistance, our data from this and other studies point to the fact that extra virgin olive oil intake improves insulin sensitivity,” they added.
By comparing the effects of different diets, the researchers also could better explore how extra virgin olive oil consumption affects the potential mutation of liver gene expression.
“The constant intake of extra virgin olive oils, for long periods, affected the expression of genes involved in oxidative stress, inflammation, lipids metabolism and fibrosis in the liver,” Martín and Kleemann said. “This is the reason why mouse livers were unable to improve the damage caused by high-fat hyper-caloric diets, despite the intake of healthy fats.”
However, the two scientists stressed that these findings were made in mice and could not be automatically correlated with humans. The reason for this, the researchers said, was the mice were eating far larger quantities of extra virgin olive oil and polyphenols, relative to their overall caloric intake, than humans naturally would.
“We believe that olive oils, even those with high polyphenols, are one of the most beneficial consumer oils we have available,” Martín and Kleemann said. “A big difference between all kinds of mouse studies and regular human olive oil consumption is that the mice get the same food every day.”
In the future, the researchers said that they hope to test olive oil in alternate dietary regimens and compare these with other consumer oils or dietary fats.
“The real benefit of consuming olive oil may be the ability to restore and quench dysmetabolic or inflammatory processes evoked by other components of the diets, such as carbohydrates, proteins, other oils and so on,” Martín and Kleemann said. “Because of the properties of olive oil, it can be expected that olive oil may be more powerful in restoring dysmetabolism and associated inflammation relative to other consumer oils.”
Regarding the effect of polyphenols, alternating a diet should also be considered by future studies.
“The effects observed in our study suggest that if high amounts of polyphenols are consumed with every bite eaten, this may be negative for the body’s own endogenous antioxidant systems,” Martín and Kleemann said. “It is possible that the endogenous antioxidant systems are down-regulated in response to the constant intake of polyphenols at relatively high levels.”
“In future studies, we should try to mimic a more alternated consumption of these dietary goodies so that the body’s antioxidant systems do not become lazy and remain active as well,” they concluded. “Thus nutritional antioxidants plus the body’s mechanisms should act in concert and synergistically instead of replacing each other.”