Across Pakistan, fried food is a regular part of daily life. Children and adults commonly eat samosas, pakoras, fries, fried chicken, jalebi, and other snacks purchased from roadside stalls, school canteens, restaurants, and markets. To reduce costs, some vendors may continue using the same oil through several frying cycles. Repeated heating gradually darkens and thickens the oil, reduces its natural antioxidants, and produces oxidized fats, aldehydes, lipid peroxides, and other harmful compounds. Studies of oils used by local food vendors have reported chemical changes associated with repeated heating, including increased oxidation, hydrolysis, and thermal degradation.paspk+1 Cancer begins when genetic material inside a cell becomes damaged and mutations accumulate. Repeatedly heated oil may contribute to this process through oxidative stress. During prolonged heating, unstable molecules called free radicals and reactive oxygen species are formed. When these substances exceed the body’s antioxidant defenses, they can attack DNA, proteins, and cell membranes. Oxidative DNA damage may create errors during DNA replication. If repair systems fail, these errors can become permanent mutations in genes that normally control cell division, DNA repair, and programmed cell death.pmc.ncbi.nlm.nih+1 The chemical products of overheated oil can strengthen this process. Lipid peroxides break down into reactive aldehydes, including malondialdehyde and related compounds. These substances can attach to DNA and form abnormal chemical structures called DNA adducts. If a DNA adduct is not repaired correctly, the cell may copy the damaged information during replication, producing a mutation. In addition, cooking-oil fumes can contain PAHs, benzene, formaldehyde, and heterocyclic aromatic amines. PAHs can be converted inside the body into active metabolites that bind to DNA; unrepaired damage may then become a cancer-promoting mutation.pmc.ncbi.nlm.nih+1 Repeatedly heated oil may also create a chronic inflammatory environment. Oxidized fats can disturb cell membranes, stimulate inflammatory signaling, and increase the production of further reactive oxygen species. Persistent inflammation causes repeated tissue injury and repair. Each cycle of cell division creates another opportunity for damaged DNA to be copied incorrectly. Over time, a cell containing several important mutations may escape normal controls, multiply excessively, invade surrounding tissues, and eventually form a malignant tumour. This does not mean that eating one fried snack will cause cancer. The concern is long-term and repeated exposure to food prepared in severely degraded oil, together with exposure to frying fumes and other dietary and environmental risk factors. Research on repeatedly heated oils has demonstrated oxidative stress, lipid peroxidation, DNA damage, genotoxic effects, and precancerous tissue changes.pmc.ncbi.nlm.nih+1 Safer choices Prefer fresh, home-prepared food when possible. Avoid oil that is very dark, foamy, thick, rancid-smelling, or smoking. Do not repeatedly reuse frying oil. Do not mix fresh oil with old, degraded oil. Remove burnt food particles from oil during cooking. Keep frying temperatures controlled and avoid prolonged heating. Improve ventilation when frying indoors. Limit frequent consumption of street-fried and deep-fried foods, especially for children. Repeatedly heated oil is therefore more than an issue of taste or nutrition. Through oxidative stress, DNA damage, inflammation, and exposure to reactive chemical compounds, degraded oil can create conditions that support the development of cancer. The simplest preventive message is clear: use fresh oil, avoid smoking temperatures, reduce repeated reuse, and make fried foods an occasional rather than everyday part of the diet.
