Do you love your chips mwitu, smokies or mandazis? Chances are they were fried in used and reused oil

Cooked mandazis. (Denish Ochieng, Standard)

For the past two years, John Ngaruiya has been running a food eatery in the heart of Mathare, an informal settlement where many residents depend on such outlets to satisfy their hunger.

On any given day, his eatery is buzzing with customers eager to enjoy his chips, mandazis and chapatis, often washed down with a cup of tea or a glass of water.

To cut costs and maximise profits, Ngaruiya relies on used cooking oil (UCO) for deep frying, unaware of the risks he is exposing to both his customers and himself.

Many eateries follow a similar practice, reusing oil multiple times, even after it has passed its safe usage limit. Some low-end, unregulated food outlets even buy UCO discarded by large hotels in the city, where such oil is often sold to recyclers.

While recycling used cooking oil can help reduce environmental pollution, it unfortunately also finds its way back to consumers, particularly in informal settlements.

Alarming levels

In Kenya, companies collect used cooking oil for recycling into products like soap or biofuels. However, some of this waste oil ends up being consumed by unsuspecting Kenyans, either at home or in eateries.

Despite the known dangers of UCO, it remains in high demand in settlements like Mathare, Korogocho, Soweto, Kibra, Mukuru, Lunga Lunga, Kawangware and Kangemi. Here, many hotel owners use it to prepare food that is consumed by thousands.

A study conducted six years ago revealed that the use of such oil had reached alarming levels.

The research, which focused on fried foods like fish, potato chips, crisps, mandazis and samosas, concluded that these foods posed a serious public health risk.

Researchers from Jomo Kenyatta University of Agriculture and Technology (JKUAT) collected and tested frying oils from low-end eateries in Nairobi, finding most of them unfit for human consumption.

“Our results show that most of the fresh, in-use, and discarded oil samples were unfit for consumption,” said Michael Wawire, a lecturer at the Department of Food Science and Technology and co-author of the study.

The study found that the degradation in all discarded oil samples far exceeded the maximum level recommended by regulatory bodies.

Dr Wawire explained that overcooked or adulterated frying oil changes its chemical composition, becoming potentially toxic.

“Degraded oils are actually toxic in nature, which means that their build-up in the human body can lead to serious health complications,” he said.

Experts warn that repeatedly heating oil can have detrimental effects on health. The process of heating oil produces harmful lipid peroxidation products, which are linked to diseases like cancer and heart complications.

“I didn’t know that reusing cooked oil is harmful. I’ve seen others doing it and decided to follow suit to save on costs,” says Ngaruiya, a 45-year-old father, when The Nairobian caught up with him at his eatery.

He adds: “Don’t blame restaurant owners for using reused cooking oil if it’s dangerous as you say. It’s because of the high cost of living. If we replaced cooking oil after using it once, we would make huge losses.”

Where is the evidence?

When he is not relying on the cheaply available waste oil, Ngaruiya reuses a five-litre jerrican of cooking oil purchased from a supermarket, which he uses until it’s completely depleted.

“Throwing it away is not an option these days,” he says.

In Embakasi’s Tassia estate, roadside potato chips seller Peter Mwania has been using reused cooking oil for more than three years. He got the idea from a friend who ran a restaurant before it closed in 2021 during the Covid-19 pandemic.

“I visited his hotel in 2019 and found him using waste oil to cook. He admitted using it, even though he knew it wasn’t good,” Mwania said.

Despite being aware of the health risks, Mwania insists that none of his customers has ever complained.

“I’ve never had a customer tell me that my chips affected them. If reused oil is dangerous, let someone bring the evidence,” says Mwania, who refused to be photographed while cooking.

Caroline Adhiambo, a fishmonger in Pipeline estate, has been using degraded cooking oil for a long time. When we met her, a queue of customers was waiting for their fish to be deep-fried. She readily admitted using waste oil.

“It’s been six years of frying fish here. If used cooking oil is really harmful, as people say, I wouldn’t have any customers. I would have gone back to my village in Siaya County to farm,” says Adhiambo.

Struggling with the high cost of living and lack of awareness, many restaurant owners and roadside food vendors across the country continue to serve food cooked in waste oil.

The demand for used cooking oil has been on the rise, driven by the sharp increase in the cost of fresh oil.

According to the Edible Oil Manufacturers Association of Kenya, the introduction of a new tax on crude palm oil has exacerbated the situation.

For example, a 20-litre jerrican of cooking oil that previously retailed at Sh3,800 now costs Sh4,200.

Crude palm oil is a key ingredient in the production of cooking oil, and a 10 per cent import duty on it came into effect on July 1, 2024, as part of Kenya’s implementation of the East African Community common external tariff.

However, according to Columbia University’s Go Ask Alice! column, reusing cooking oil can be safe if certain precautions are followed. To reuse oil, it must be heated to between 175 and 192 degrees Celsius.

“Frying foods at or above 190 degrees Celsius can alter the chemical composition of fats in the oil, producing new substances known as lipid degradation products,” the article states.

These products are linked to increased risks of stroke, atherosclerosis, high cholesterol, Alzheimer’s, Parkinson’s and liver diseases.

Medical News Today, in an article titled ‘Frequently reusing frying oil may accelerate brain damage’, explains that heating oils to high temperatures significantly alters their chemical structure, reducing beneficial antioxidants and forming harmful compounds such as trans fats, acrylamide, and aldehydes.

“Reheating oils, especially for deep-frying, makes the oil increasingly unstable, reducing its health benefits and generating more toxins with each use,” the article adds.

The liver, which detoxifies the body, may be particularly vulnerable to damage from reheated oils.