A new study has found a concerning link between cooking oil that has been reused multiple times and late-stage breast cancer. The research, which involved lab mice fed reused cooking oil, found that consuming this ‘thermally abused’ oil may trigger changes that promote metastases and the proliferation of aggressive cancer cells. Similar effects weren’t observed in mice fed fresh cooking oil.
The research comes out of the University of Illinois, where researchers evaluated the effects of ‘thermally abused’ cooking oil on mice who had received an injection of 4TI breast cancer cells in their tibias. These cells are described as an aggressive form of breast cancer known for spontaneously metastasizing in other parts of the body, such as the lungs and lymph nodes.
At the start of the study, lab mice were fed a low-fat diet for one week, after which point one group was switched to reused cooking oil and another group was fed fresh soybean oil. In this case, reused cooking oil refers to frying oil that had been repeatedly heated to high temperatures, then cooled, such as the oil used by fast food restaurants to cook fries.
Both groups of mice were fed these diets for 16 weeks. By the 20th day of the study, the mice given reused cooking oil had more than four times the number of metastatic cancer tumors as the group of mice given fresh soybean oil. As well, the reused cooking oil group had more lung cancer metastases than the fresh oil group.
In addition, the researchers found that the tumors in mice fed reused cooking oil were ‘more aggressive and invasive’ than in the fresh oil group, highlighting a concerning effect consuming old cooking oil may have on breast cancer patients and survivors.
Talking about the effects is study lead professor William G. Helferich, who said:
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.
According to the study, reused cooking oil that has been repeatedly heated to high temperatures experiences a breakdown of triglycerides, leading to the oxidation of free fatty acids and the release of a toxic carcinogen called acrolein. Past research has linked the acrolein in thermally abused cooking oil with other health problems, such as heart disease and atherosclerosis.
Though humans do not directly consume reused cooking oil on its own, many people passively get it in their diet when consuming fried foods. This reuse is a standard practice among many restaurants, particularly fast food joints, where the cost of using fresh oil every day would be substantial.