Do you reuse cooking oil? It could be detrimental to your health, according to a new study.
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Researchers from the University of Illinois at Urbana-Champaign recently conducted a study, published in the Cancer Prevention Research journal, to determine how reusing cooking oil impacts the progression of breast cancer.
To do so, they examined mice that were injected with breast cancer cells and then grouped them into two categories. After eating a low-fat diet for a week, the first group of rodents was fed unheated soybean oil, and the second group had “thermally abused” or reused oil for the next 16 weeks. They said they used soybean oil because it’s most commonly used by the food service industry in deep frying.
After 20 days, the mice that consumed reused oil had four times as much metastatic growth, cancer that spread from its original site to another, compared to the mice that were fed fresh soybean oil.
Upon further analysis, they observed there was more metastates in the lungs of the animals that consumed the resused oil.
"There were twice as many tumors in the lung, and they were more aggressive and invasive," said coauthor William G. Helferich said in a statement.
“I just assumed these nodules in the lungs were little clones – but they weren’t,” Helferich continued. “They’d undergone transformation to become more aggressive. The metastases in the fresh-oil group were there, but they weren’t as invasive or aggressive, and the proliferation wasn’t as extensive.”
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Why is reusing cooking oil so harmful?
The scientists found the growing lung tumors in mice that consumed the reused cooking oil produced more Ki-67, a key protein associated with rapid cell growth. They also said this group had liver issues as well as gene alterations, which were associated with oxidative stress and the metabolism of foreign substances.
“When oil is repeatedly reused, triglycerides are broken apart, oxidizing free fatty acids and releasing acrolein, a toxic chemical that has carcinogenic properties,” the team explained. “As the oil degrades, polymer molecules also accumulate, raising nutritional and toxicological concerns.”
The authors noted countries in Europe regulate the amount of polar materials in frying oils. Polar materials are “chemically altered triglycerides and fatty acids that are used as chemical markers of oils’ decomposition,” the analysts said. Typically, restaurants can only use oil with 24-27 percent of polar material.
The reused oil in the study contained 15 percent of polar material, while the fresh soybean oil only had 2-4 percent.
“Because there are no regulations in the U.S., it’s really difficult for us to evaluate what’s out there,” coauthor Nicki Engeseth said. “But the important thing is, the food that’s fried in these oils sucks up quite a bit of oil. Even though we’re not consuming the oil directly, we’re consuming oil that’s brought into the food during the frying process.”
The researchers concluded that more evaluations are needed, but they said they believe diet “provides an opportunity to reduce breast cancer survivors’ risk.”
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