People who consume food cooked using thermally abused oil may be more likely to develop late-stage breast cancer, a new study says.

In a study featured in the journal Cancer Prevention Research, scientists at the University of Illinois in Urbana-Champaign examined the health effects of cooking oil that has been used multiple times at high temperatures.

They found that consuming such oils can result in the proliferation of tumor cells and metastases, as well as change the metabolism of lipids in the body.

Thermally Abused Cooking Oil

William G. Helferich, professor of food science and human nutrition at Illinois, led his colleagues in studying the impact of thermally abused cooking oil on health. They focused their research on oil made from soybean because it is commonly used in deep frying by many in the foodservice industry.

The researchers had mice undergo a low-fat diet for a week before dividing them into two groups. The first group was given unheated soybean oil, while the other one was fed with thermally abused oil. Both groups followed this diet for 16 weeks.

The animals were then injected with 4T1 breast cancer cells to simulate late-stage breast cancer. The 4T1 cells are known to cause an aggressive version of cancer capable of metastasizing at different parts of the body spontaneously. This form of the illness can often be found in patients' lymph nodes, lungs, and liver.

Helferich and his team observed the mice for 20 days after they had been inoculated with the cancer cells. They found the animals that were fed with thermally abused oil were more than four times more likely to have their primary tumors metastasize compared to those that were fed fresh soybean oil.

The animals that consumed the spoiled oil also had more metastasized tumors in their lungs.

"There were twice as many tumors in the lung, and they were more aggressive and invasive," Helferich noted.

Higher Likelihood For Metastasized Tumors

The researchers initially thought that nodules in the mice's lungs were clones, but they found that this was not the case. The tumors had actually undergone transformation and had become more aggressive than before.

While the mice that were fed fresh soybean oil also developed metastases of their tumors, these were not considered as aggressive or invasive as the ones found in the second group. The proliferation of the cancer cells in the first group of mice was also not as widespread.

Helferich and his colleagues examined both groups of mice to check how their lung tumors had metastasized. The tumors found in the second group produced more Ki-67, a key protein that is linked with the proliferation of cells.

The researchers also looked at the gene expression of the mice's livers. By analyzing the RNA sequencing of the animals' organs, they saw 455 genes that had either had two times greater, or two times lower likelihood of expression when compared to those that were fed only fresh soybean oil.

Study co-author Ashley W. Oyirifi said these altered pathways for the animals' genes were linked with oxidative stress. They are also associated with the metabolism of foreign substances.

Using cooking oil repeatedly can increase its likelihood to cause negative health effects. The process causes triglycerides to break apart more often and oxidize free fatty acids. It can also release acrolein, a chemical that is known to cause cancer development.

The study's findings help raise concern about the potential health risks associated with thermally abused oil. While people do not consume these oil directly, they are still exposed to its negative effects. Food that has been prepared using spoiled oil still contains the substance by the time they are eaten.

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