By David W. Brown
Cooking oils are marketed as everyday essentials, but scientific evidence shows they can be detrimental to human health. The issues arise from the way oils are produced, their biochemical effects in the body, and the toxic solvents used during extraction, particularly hexane.
Industrial Processing and Hexane Extraction
Most commercial cooking oils—soybean, corn, canola, sunflower, safflower, and others—are not simply “pressed” from plants. Instead, they undergo industrial solvent extraction, where the seeds are crushed and treated with hexane, a petroleum-derived chemical. Hexane is favored because it efficiently strips nearly all oil from plant material, maximizing yield. After extraction, the oil is heated to evaporate most of the hexane, but residues can remain. Even trace levels of hexane are concerning: it is classified as a neurotoxin and inhalation exposure is linked to nerve damage in workers. While regulators argue the amounts left in oil are small, chronic dietary exposure has not been thoroughly studied. Thus, oils made with hexane introduce a potential chemical contaminant into the human food supply.
Refining, Bleaching, and Deodorizing
After extraction, oils are refined, which involves neutralizing free fatty acids with lye, bleaching with clays to remove pigments, and deodorizing at very high heat to strip unpleasant odors. This high-heat treatment alters the chemical structure of fatty acids, generating trans fats and other oxidative byproducts even before the oil reaches consumers. Many of these compounds are pro-inflammatory and cytotoxic, setting the stage for long-term health consequences.
Oxidation and Free Radical Damage
Once extracted, refined oils are chemically unstable. Polyunsaturated fatty acids (PUFAs) in oils like soybean and corn are highly prone to oxidation, especially when exposed to light, air, and heat during cooking. Oxidized oils form lipid peroxides and aldehydes, which can damage DNA, proteins, and cell membranes. These compounds trigger oxidative stress and inflammation, both fundamental drivers of chronic diseases including cancer, atherosclerosis, and neurodegenerative disorders.
Distortion of Omega-6 to Omega-3 Ratio
Vegetable oils are extremely high in omega-6 fatty acids (linoleic acid) but nearly devoid of omega-3s. While omega-6 fats are essential in small amounts, modern diets laden with cooking oils push the ratio of omega-6 to omega-3 far beyond the ideal balance (often 20:1 versus the recommended 1–4:1). Excess omega-6 promotes the production of pro-inflammatory molecules called eicosanoids, fueling systemic inflammation that underlies arthritis, cardiovascular disease, diabetes, and obesity.
Impact on Human Metabolism
Refined oils are calorie-dense but nutrient-poor, offering no fiber, vitamins, or minerals. They represent “empty calories” that disrupt satiety signals and contribute to weight gain. Furthermore, heating oils during frying produces advanced lipid oxidation end products (ALEs), which impair insulin signaling and promote insulin resistance. This helps explain the strong association between frequent fried food consumption and type 2 diabetes.
Cooking oils may seem harmless, but their risks are embedded at every stage: toxic solvent extraction with hexane, chemical refining and deodorizing, oxidative instability, omega-6 overload, and pro-inflammatory byproducts formed during cooking. Regular consumption exposes the human body to free radical damage, chronic inflammation, and toxic residues, which together contribute to obesity, diabetes, cardiovascular disease, and cancer. For optimal health, whole plant foods such as nuts, seeds, and avocados provide natural fats along with fiber, vitamins, and antioxidants—delivering the benefits of healthy fats without the hazards introduced by industrially processed oils.