Can frying oil be reused?

Neurodegeneration has even been found in the offspring of rats that ate reused oil.

An alarming new study has revealed that consuming reused cooking oil can lead to higher levels of neurodegeneration in rats and their offspring. Given that the practice of reheating the same batch of oil for multiple meals is common in households and restaurants worldwide, the study's findings could have significant implications for human health.

Deep-frying involves completely submerging food in hot oil and is an extremely popular cooking technique that can be used to prepare everything from doughnuts to falafel. Unfortunately, the delicious food that comes out of deep fryers has been linked to a number of diseases, including cancer and diabetes.


These dangers are thought to increase when oils are reused, because repeated heating destroys the antioxidants and other healthy components contained in the oil, while adding dangerous compounds such as trans fats and peroxides. But until now, the consequences of consuming reused oil have not been properly researched.

"Deep-frying at high temperatures has been associated with various metabolic disorders, but there have been no long-term studies on the impact of deep-fried oil consumption and its detrimental effects on health," study author Kathiresan Shanmugam said in a statement. "To our knowledge, this is the first time we report that long-term deep-fried oil supplementation increases neurodegeneration in first-generation offspring."


For 30 days, the researchers fed female rats either standard chow or food enriched with regular or reheated fats. At the end of the month, they found that the animals fed the reused fat had elevated liver enzyme levels, indicating high levels of inflammation and oxidative stress in this key organ.

"As a result, liver lipid metabolism was significantly altered and transport of the important brain omega-3 fatty acid DHA was reduced," Shanmugam said. "This resulted in the neurodegeneration seen in the brain histology of rats and their offspring that consumed the reheated oil."

These findings demonstrate the importance of the liver-gut-brain axis and how disruption of this axis can lead to neurological damage. Furthermore, rats fed reheated fat showed increased cholesterol and higher levels of inflammatory markers such as high-sensitivity C-reactive protein (hs-CRP), which has been linked to heart attacks and strokes.

Cellular damage in the colons of these rats and degeneration of neuronal support cells known as glia were also noted by the researchers. In a series of follow-up experiments, the study authors exposed the rats to monosodium glutamate (MSG) and found that this common food additive caused more neurological damage in rats raised on reused oil.

The results of the study were presented at Discover BMB, the annual meeting of the American Society for Biochemistry and Molecular Biology, held March 23-26 in San Antonio.

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