Repeated consumption of sunflower oil induced fibrosis, increased oxidative stress and inflammation in the rats’ livers, leaving them vulnerable to non-alcoholic steatohepatitis (NASH). NASH iscan result from worsening of non-alcoholic fatty liver disease (NAFLD) and can be a precursor to cirrhosis or liver cancer. Sunflower oil contains mainly omega-6 polyunsaturated fatty acids, which have previously been linked to inflammaton when consumed in excess.
Different types of fats (sunflower oil, virgin olive oil and fish oil), were fed to rats from weaning until the animals were 24 months old. The impact of the dietary oils on fat accumulation was analysed by the research team from the University of Granada, Spain.
The scientists also examined changes over time in liver structure, fibrosis, oxidative stress, gene expression and telomere length (a biomarker of ageing).
Liver fat accumulation occurred with ageing, irrespective of the type of oil fed to the rodents. However, other changes to the organ, which took place between the ages of 6 and 24 months, were markedly different according to the type of oil consumed.
“Virgin olive oil led to the lowest oxidation and ultrastructural alterations [to the liver]. Sunflower oil induced fibrosis, ultrastructural alterations and high oxidation. Fish oil intensified oxidation associated with age, lowered electron transport chain activity and enhanced the relative telomere length,” observed senior researcher Professor José Luis Quiles.
Olive oil best for liver
Perhaps surprisingly, the age-related oxidative effect of lifelong fish oil consumption also elevated NASH risk, the scientists noted. Virgin olive oil was the most beneficial in respect of long-term liver health.
“Virgin olive oil might be considered the dietary fat source that best preserves the liver during the ageing process,” concluded Quiles.
Virgin olive oil contains not only a large proportion of monounsaturated fatty acids (MUFA), but is also rich in polyphenols. By contrast, sunflower oil and fish oil contain only small or trace amounts of these antioxidant phytonutrients. Previous research, both in vitro and in vivo, has demonstrated that polyphenols have a protective against oxidative stress.
Despite their conclusion that olive oil is the best dietary source of fat for liver health, they do not comment on whether the benefits are derived from the MUFA or from the polyphenols.
Source: Journal of Nutritional Biochemistry
Volume 52, pages 36-44. DOI: 10.1016/j.jnutbio.2017.09.007
“Gene pathways associated with mitochondrial function, oxidative stress and telomere length are differentially expressed in the liver of rats fed lifelong on virgin olive, sunflower or fish oils”
Authors: Alfonso Varela-Lopez, José Luis Quiles et al.