Health Risks in Puri and Singara Fried in Burnt Oil: Experts Warn of Heart Disease to Cancer

At a recent seminar in Dhaka, concern was raised over the widespread use of burnt, repeatedly reheated oil in preparing popular snacks in Bangladesh. Experts said the oil, reused again and again, raises the risk not only of stomach problems but also of high blood pressure, heart disease, heart attacks, liver damage and even cancer.

Every afternoon, crowds gather at fried-snack stalls in lanes and alleys. Oil bubbles in pans as puri, singara, samosa and piyaju are dropped in. In many places, the same oil is used for frying from morning to night, turning black and foaming — and it is in that oil that many people's favourite snacks are cooked.

Professor Dr Mohammad Shoeb of the University of Dhaka's chemistry department said the chemical structure of edible oil begins to change as soon as it is heated once. Edible oil contains various chemical components, held in oil-glyceride form or as unsaturated fatty acids.

When heated to a certain temperature, the fatty acids in the oil change into a trans configuration, producing trans fat. Dr Shoeb said this trans fat is harmful to health and can lead to cardiovascular disease, which blocks the arteries of the heart.

High heat also produces many chemical substances such as aldehydes, which react with different cells in the body. Experts said that when the same oil is heated repeatedly or used for a long time, its necessary components change into harmful ones.

Reusing burnt oil can also increase the risk of acidity, heartburn, stroke, Parkinson's disease, heart disease and even cancer, experts said. Harmful compounds form in oil heated repeatedly at excessive temperatures.

Experts added that invisible particles from earlier cooking remain in reused oil, so even fresh food cooked in it loses much of its taste and, in particular, its nutritional value. Dr Shoeb said free radicals form in used oil, damaging human cells and accelerating the ageing process.

Md Shafiqul Islam, chairman of the Bangladesh Food Safety Authority (BFSA), called burnt oil severely harmful to the heart and urged people to avoid using it. He said that of all the heart's enemies, the most deadly is burnt oil, and that food businesses, as well as individuals, must give up using it.

Public health specialist Dr Mushtaq Hossain believes burnt oil, or oil used more than once, works in the human body as a slow poison. He said eating food cooked in burnt oil day after day can create risks of high blood pressure, heart disease, heart attack, fat deposits in blood vessels, liver damage and cancer.

Dr Mushtaq Hossain said that once edible oil is used, the oxygen in it leaves, and consuming such oil causes blood to clot in the body, affecting the heart and the brain. He warned that using the oil for a long time risks leaving many important organs inactive. In his words, burnt oil accumulates in the blood as waste, and prolonged use reduces circulation, creating a risk of infection and failure in vital organs such as the heart and brain.

The same seminar also raised another side of the issue. Experts said that if discarded burnt oil were collected and turned into biofuel or biodiesel, it would both reduce environmental pollution and bring economic benefit. In their view, used edible oil can be converted into biodiesel through scientific methods and used as a renewable fuel to cut natural pollution.

In Bangladesh, the private company Biotech Energy Limited collects cooking oil and produces biodiesel from it. According to the company, it can collect as waste only about 30 percent of the edible oil used in restaurants and fried-snack shops in the country.

Abdullah Al Hamid, managing director of Biotech Energy Limited, said the company now collects more than 100 tonnes of used cooking oil every month from at least 3,000 establishments. He said that from places serving both curries and deep-fried food, not a single drop of oil comes in, because the leftover oil is put into the dough for parathas. In other words, oil left after one round of frying is not thrown away but reused in paratha dough or curries.

Abdullah Al Hamid said that although there was little response when collection of used edible oil began, volumes have risen since 2019; where initially even five tonnes could not be found, the company now collects up to 100 tonnes a month. He said biofuel production in Bangladesh is currently small in scale, and most of it is exported to various European countries.

Dr Mohammad Shoeb said the fatty acids in burnt oil, held as triglycerides, are converted with methanol into esters, and in chemical terms the esters of various fatty acids are biodiesel or biofuel. As food oil contains no sulphur, he said, the biodiesel made from it contains none either, producing 80 percent less black smoke than ordinary diesel.

Experts also noted, however, that the infrastructure and technical capacity needed to produce biofuel this way are quite costly. Biofuel production has not yet reached a large scale in Bangladesh, but they said the situation is gradually changing.