Deep-frying is a popular form of food preparation used globally and throughout in the United States. Each time dietary oils are heated to deep-frying temperatures, they undergo chemical alterations that result in a new matrix of lipid structures. These lipid products include triglyceride dimers, polymers, oxidized triglycerides, and cyclic monomers, which raises nutritional concerns about associations between these lipid products and heightened health risks.
Although, the correlation between thermally abused frying oil and deleterious health outcomes currently exist, yet there is less information concerning the effects of thermally abused frying oil consumption and the progression of breast cancer. In a new study by the University of Illinois, scientists suggest that consuming the chemical compounds found in thermally abused cooking oil may trigger genetic changes that promote the progression of late-stage breast cancer.
Scientists found that reused cooking oil may act as a toxicological trigger that promotes tumor cell proliferation, metastases and changes in lipid metabolism.
For the study, scientists used soybean oil as it is widely used in cooking industry in deep frying. Then scientists fed one group of the mice with fresh soybean oil and another group consumed thermally abused oil for the next 16 weeks.
Scientists then simulated late-stage breast cancer by injecting 4T1 breast cancer cells into a tibia of each mouse. The 4T1 cells are an aggressive form of the disease that can spontaneously metastasize to multiple distant sites in the body, including the lungs, liver and lymph nodes.
Twenty days after inoculation with the tumor cells, the primary tumors in the tibias of the mice that consumed the thermally abused oil had more than four times as much metastatic growth as the mice that consumed the fresh soybean oil. And when the researchers examined the animals’ lungs, they found more metastases among those that consumed the thermally abused oil.
William G. Helferich, a professor of food science and human nutrition said, “There were twice as many tumors in the lung, and they were more aggressive and invasive. I just assumed these nodules in the lungs were little clones – but they weren’t. 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.”
When studying both groups of mice, scientists found that the metastatic lung tumors in those that consumed thermally abused frying oil expressed significantly more of a key protein, Ki-67, which is associated strictly with cell proliferation. In addition, the gene expression in these animals’ livers was altered as well.
Using RNA sequencing, scientists found that 455 genes in which expression was at least two times greater – or, conversely, two times lower – than in mice that consumed the fresh oil. The altered gene pathways were related to oxidative stress and the metabolism of outside substances.
When the oil is repeatedly reused, triglycerides are broken apart, oxidizing free fatty acids and releasing acrolein, a toxic chemical that has carcinogenic properties.
Food chemistry professor Nicki J. Engeseth said, “Because there are no regulations in the U.S., it’s really difficult for us to evaluate what’s out there. 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.”
Helferich said, “Breast cancer survivors’ biggest fear is a recurrence, and the majority of these survivors have dormant tumor cells circulating in their blood. What wakes those cells up is anybody’s guess, but I’m convinced that diet activates them and creates an environment in different tissues that are more fertile for them to grow.”
Graduate student Ashley W. Oyirifi said, “Many cancer biologists are trying to understand what’s happening at metastatic sites to prime them for tumor growth. We’re trying to add to this conversation and help people understand that it might not be just some inherent biological mechanism but a lifestyle factor. If diet provides an opportunity to reduce breast cancer survivors’ risk, it offers them agency over their own health.”
Additional co-authors on the study were Urszula T. Iwaniec and Russell T. Turner, both of Oregon State University; and Fureya (Yunxian) Liu, a then-graduate student at the U. of I.
The study is reported their findings in the journal Cancer Prevention Research.