Danger of eating reused cooking oil

New research links it to breast cancer

| THE INDEPENDENT | More Ugandans are consuming fast-food than in the past. According to a study titled `Determinants of fast food consumption in Kampala’ by Sarah Ayo, Jackline Bonabana-Wabbi, and D. Sserunkuuma, Chips, deep fried chicken, fish, and meat, sausages, chaps, pizza, and kebabs are among the most consumed fast foods.

Almost all are cooked by deep frying in cooking oil which, according to new research, can cause cancer if not done properly. Apart from the other health concerns linked to consumption of fatty meats which are associated with fast food, researchers are increasingly pointing at danger thought to be resulting in the tendency to reuse cooking oil in fast food preparation.

According to the research, reusing oil creates free radicals, a type of molecule, that attach themselves to healthy cells and may cause diseases, including cancer.

Consuming food prepared using reused oil over long periods also has a risk of causing acidity, heart disease, Alzheimer’s and Parkinson’s disease, and irritable throat.

Specifically, a recent study has shown that thermally-abused or reheated cooking oil possibly triggers cell changes that can promote late-stage breast cancer growth.

The study is interesting because the incidence of breast cancer in Uganda has nearly tripled in three decades and the cause of this is not wholly understood.

According to 2014 statistics from the Kampala Cancer Registry the prevalence of breast cancer in women stands at 3.7% or four women out if every 100 having the disease.

Researchers from the University of Illinois at Urbana-Champaign tested “thermally abused frying oil,” which is cooking oil that has undergone reheating to high temperatures multiple times, in laboratory mice and found that it increased metastatic breast cancer growth.

The team reported these findings in the journal `Cancer Prevention Research’.

The scientists fed all of the lab mice a low-fat diet for a week. Then, they gave some of the mice unheated fresh soybean oil for 16 weeks while the rest ingested thermally abused oil instead.

They chose to use soybean oil because the restaurant industry commonly uses it for deep frying.

To simulate breast cancer, they injected 4T1 breast cancer cells into a tibia of each mouse. These breast cancer cells are very aggressive and have a high rate of metastasis to multiple distant sites. As a result, they often appear in the lymph nodes, liver, and lungs.

The effects of reused oil

At 20 days after the injection of the tumor cells, there was a notable difference in the rate of metastatic growth between the two groups of mice. In the mice who had eaten thermally abused oil, the metastatic growth of the tibia tumors was four times greater than that of the tumors in the mice who consumed the fresh oil.

There were also more lung metastases in the former group. Lead researcher William G. Helferich, a professor of food science and human nutrition, noted that there were twice as many lung tumors, which were also more aggressive and invasive than those in the fresh-oil group.

“I just assumed these nodules in the lungs were little clones — but they weren’t,” says Helferich. “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.”

Here’s what needs to be done

Fast-food is popular because it is seen as an easy solution to consumers’ busy schedules and limited meal preparation time.

The research shows that as the population grows and feeding tastes continue changing coupled with the need for convenience, consumption of fast-food is expected to rise even higher; especially in urban areas.

The trouble is that although the danger of cooking with re-used cooking oil is known, it is not practical in the fast food industry to use new oil every time. The practical approach is to reuse oil but limit the duration of its use and hopefully reduce its negative effects.

Unfortunately, there is no set number to how many times one can reuse the oil. This depends on many factors; including type of oil used, how long the oil remains heated, and what was deep fried.

Anyone routinely cooking with reused oil could try to reduce its negative effect by:

• Ensuring that leftover oil from cooking or frying is cooled and properly sieved to remove food particles before being store; preferably in an airtight container. Food particles in used oil spoil it.
• Avoid using oil that is darker and greasier or thicker than usual.
• Avoid oil that emits a lot of smoke when heated. This shows the oil has accumulated HNE which is a toxic substance suspected to cause diseases including Parkinson’s, Alzheimer’s, stroke, and liver disease.
• Use oils that have a high smoke point i.e. they do not break down at high temperatures. These include oil from sunflower, soybean, sim sim and so on. Oils with a low smoke point such as olive oil should never be used for deep frying.

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