Eating food deep-fried in oil not only adds calories but also poses several health risks. Researchers have now found that frequent reuse of frying oil, a common practice in many homes and restaurants, could raise the risk of neurodegeneration and brain damage.

According to the results of a rat study presented at Discover BMB 2024, the American Society for Biochemistry and Molecular Biology's annual meeting, diets containing reheated cooking oils led to significantly increased levels of neurodegeneration compared to a standard diet.

"Deep-frying at high temperatures has been linked with several metabolic disorders but there have been no long-term investigations on the influence of deep-fried oil consumption and its detrimental effects on health. To our knowledge we are first to report long-term deep-fried oil supplementation increases neurodegeneration in the first-generation offspring," said Kathiresan Shanmugam, an associate professor from Central University of Tamil Nadu, India, who led the study.

The rats participating in the study were divided into five groups. Each group was given either standard chow alone or standard chow supplemented with 0.1 ml per day of unheated sesame oil, unheated sunflower oil, reheated sesame oil, or reheated sunflower oil for 30 days. The reheated oils were used to simulate the effects of reused frying oil.

The rats that consumed reheated sesame or sunflower oil had elevated oxidative stress and inflammation in the liver. They also had significant damage to the colon and associated changes in endotoxins and lipopolysaccharides; toxins released from certain bacteria.

The researchers noted higher levels of neurodegeneration in rats that consumed reheated oil and their offspring compared to rats on a normal diet. This is attributed to the disruption of the liver-gut-brain axis associated with the reheated oil.

"As a result, liver lipid metabolism was significantly altered, and the transport of the important brain omega-3 fatty acid DHA was decreased. This, in turn, resulted in neurodegeneration, which was seen in the brain histology of the rats consuming the reheated oil as well as their offspring," the researchers wrote.

The team conducted further experiments with the use of monosodium glutamate (MSG) to promote neurotoxicity in the rat offspring. The results showed that the offspring that took reheated oils were more likely to show neuronal damage than the control group receiving no oil or those that received unheated oil.

To cut the risk of liver inflammation and neurodegeneration, the researchers recommend supplementing with omega-3 fatty acids and nutraceuticals such as curcumin and oryzanol. However, additional human studies are needed to verify the effect.

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