Health professionals are warning against the repeated use of reheated cooking oil, describing it as a harmful practice that could lead to serious health conditions, including cancer.

With food prices rising daily and incomes stretched thin, many families now reuse cooking oil to prepare different meals to cut costs. While this may seem economical, experts warn it could have fire long-term health consequences.

In many homes, a single batch of oil is used repeatedly for frying akara, meat, plantain, and sometimes even fish. For many households, the practice is driven by the need to manage food items carefully and reduce kitchen waste.

Mrs Yetunde Afolabi*, a food vendor in Lagos, told Guardian Life that she often sieves and reuses oil after each cooking session.

“Once it’s not too dark, I still use it for stew or frying again. That’s how I save money,” she said.

However, nutritionists caution that this routine exposes families to harmful chemicals produced when oil is heated multiple times.

According to Dr Egemba Fidelis, repeatedly heating oil causes it to break down, releasing harmful substances such as free radicals, acrolein, and polycyclic aromatic hydrocarbons.

“These substances have been linked to different types of cancer and chronic health problems. The risk increases when oil is used beyond two cycles of heating,” he explained.

A report published in the Journal of Clinical Biochemistry and Nutrition supports this claim. The study found that animals fed with food fried in reused oil showed signs of liver inflammation and early-stage cancer cells in major organs.

Medical experts have identified four major cancers associated with the consumption of food cooked in overly reused oil:
The liver plays a central role in detoxifying harmful substances. Continuous exposure to degraded oil can lead to inflammation and eventual liver damage.
Some studies suggest that toxic compounds from reused oil can disrupt hormonal balance, raising the risk of hormone-related cancers.
Toxic aldehydes and free radicals formed in reheated oil can damage the inner lining of the intestine and colon.
Acrolein, a by-product of overheated oil, is known to damage cells and cause mutations that could lead to cancer.

Many households may not recognise when oil has become dangerous. But there are visible signs.

Clinical nutritionist, Odukoya Fiyintoluwa said that any oil that shows one or more of these features should not be reused: a deep brown or black colour, a thick or sticky consistency, a sharp burnt or sour smell, rapid foaming or smoking when heated, and the presence of solid residue at the bottom of the pot.

“It’s a mistake to mix bad oil with fresh oil. That does not improve its safety,” he warned.

To reduce the health risks associated with reused cooking oil, health professionals advise families to adopt safer and more practical cooking methods. These changes, though small, can make a big difference in protecting long-term health without adding pressure to household budgets.

One effective method is shallow frying, which requires less oil than deep frying. This not only reduces waste but also limits the urge to reuse oil. Experts say even simple kitchen adjustments like this can go a long way in limiting exposure to harmful substances.

Another safer option is to switch cooking methods altogether. Instead of relying heavily on frying, families are encouraged to explore steaming, boiling, stir-frying, or grilling. These techniques use little or no oil, preserve nutrients in food, and lower the risk of ingesting degraded oils.

Health professionals also recommend portion control as a preventive measure. Cooking in smaller quantities helps avoid over-frying and allows better management of oil. By using just enough oil for a single meal, there’s no need to save leftovers that may later become unsafe for consumption.

In households where palm oil is used, experts advise moderation. While palm oil has a higher heat resistance than some vegetable oils, it still breaks down when overheated or reused repeatedly. Its rich colour and flavour make it ideal for certain local dishes, but it should not be seen as a license to reuse carelessly.

Planning meals better can help reduce the reliance on frying. Rearranging the weekly food schedule to include more soups, stews, or boiled dishes will not only preserve oil but also improve overall nutrition.

Another common mistake in Nigerian kitchens is frying different food items in the same oil. For example, using oil for fish in the morning, then meat in the afternoon, and plantain at night.

Odukoya says this increases the chemical instability of the oil.

“Each food type leaves its residue in the oil. Mixing them over time not only affects the taste but creates the perfect environment for harmful compounds to develop,” he said.

While experts agree that the economic situation is challenging, they insist that safety in food preparation should remain a top priority.

Odukoya said “It’s not about wastefulness. If you’re spending less today but exposing your body to harmful substances, it could cost much more in the future, both medically and financially.”

He advised households to treat cooking oil the same way they treat other perishables: once it shows signs of spoilage, it should be discarded.

“There’s no substitute for health,” he added.

*Name changed for privacy reasons