Reusing cooking oil is something many restaurants, as well as many home cooks, do.
For instance, fry machines keep the same cooking oil in a station for entire work shifts. In that time hundreds of different food items are fried in the same cooking oil.
This common practice might save money, but there are reports indicating it could lead to accelerated breast cancer growth.
In this study, researchers at the University of Illinois tested to see how “thermally abused” cooking oil might assist in out of control growth of cancer cells.
Mice Fed Re-Heated Soybean Oil Had Worse Cancer
To discover just how reheating cooking oil over and over again might affect cancer growth the team injected 4T1 breast cancer cells into mice they planned to feed reheated cooking oil.
They injected the mice with these breast cancer cells because they’re known to be quite aggressive and are also shown to metastasis to multiple distant sites. This is why they’re commonly found in the liver, lungs, and lymph nodes.
Once injected, all the mice were given a diet of low-fat food for a week.
After the week of eating the low-fat diet the mice were split into two groups. One group ate unheated fresh soybean oil for a period of 16 weeks, the other half of the group were made to eat thermally abused oil instead (the researchers used this kind of oil because it’s a commonly used to deep fry food in restaurants.
20 days after the mice were injected with the breast cancer cells the scientists decided to observe what happened to the mice who’d been on their different diets.
What astounded the researchers was the group of mice who’d been given the reheated soybean oil had much higher rates of tumor metastasization. The growth at the site of the injection was 400% higher than the mice who consumed the fresh soybean oil
The group who ate the reheated oil also displayed many more lung metastases than the group that didn’t. One of the researchers in the study, William G. Helferich, wrote in their study that this group has 200% more lung tumors.
Not only did they have more tumors, but they were also more aggressive and invasive than those in the fresh-oil group.
Why Is Reheated Oil Bad In the First Place?
Even though the researchers aren’t exactly sure about the association between reheated oil and tumor growth, they theorize that when oil is heated up over and over it alters the composition of the cooking oil and causes acrolein to be released.
Acrolein is a toxic and potentially carcinogenic chemical.
This is disturbing because many restaurants reheat their cooking oils dozens of times a day before trading out for fresh oil.
Co-lead author and graduate student Ashley W. Oyirif 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.”