It may be budget-savvy, but reusing cooking oil may act as a trigger for breast cancer progression and cancer survivors should take note…

Do you reuse cooking oil?

It’s good for the household budget, but the bad news is that compounds in thermally abused cooking oils – reused cooking oil – may trigger genetic, biochemical changes that hasten the progression of late-stage breast cancer, promoting tumour cells’ growth and proliferation.

This is according to a new study in mice by University of Illinois scientists.

The study

After consuming a low-fat diet for one week, one group of the mice was fed unheated fresh soybean oil, while another group consumed thermally abused oil – cooking oil that has been repeatedly reheated to high temperatures – for the next 16 weeks.

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Soybean oil was used in the study because of its common use by the food service industry in deep frying.

The scientists 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 metastasise to multiple distant sites in the body, including the lungs, liver and lymph nodes, according to the study.

Twenty days after inoculation with the tumour cells, the primary tumours 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.

There were twice as many tumours in the lung, and they were more aggressive and invasive,” says William G. Helferich, a professor of food science and human nutrition, who led the research.

“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.”

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What happens when cooking oils are reused?

When oil is repeatedly reused, triglycerides are broken apart, oxidising free fatty acids and releasing acrolein, a toxic chemical that has carcinogenic properties.

Scientists have long known that thermally abused oil contains acrolein, and studies have linked the lipid peroxides in it with a variety of health problems, including atherosclerosis and heart disease.

As the oil degrades, polymer molecules also accumulate, raising nutritional and toxicological concerns.

A cautionary note for breast cancer survivors

Breast cancer survivors’ biggest fear is recurrence, and the majority of these survivors have dormant tumour cells circulating in their blood, says Helferich.

“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’s more fertile for them to grow,” he says.

“Many cancer biologists are trying to understand what’s happening at metastatic sites to prime them for tumour growth,” says one of the lead authors, graduate student Ashley W. Oyirifi, “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.”

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Source: University of Illinois at Urbana-Champaign via

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