Seed oils such as canola, sunflower, and soybean oil have come under increasing scrutiny in recent years, with claims circulating on social media labelling them as “toxic” and responsible for a range of chronic diseases. However, nutrition experts and recent scientific studies suggest that the concerns may be overstated or misinformed.
The backlash against seed oils primarily centres around their high content of omega-6 fatty acids. Critics argue that excessive consumption of omega-6 — without balancing it with omega-3 fatty acids — can trigger inflammation and contribute to heart disease, cancer, and other health issues.
Yet, leading researchers say the evidence does not support these fears. “Controlled trials show that omega-6 fatty acids do not increase inflammation,” said Dariush Mozaffarian, director of the Food is Medicine Institute at Tufts University. In fact, he notes that omega-6s produce molecules that have anti-inflammatory effects in the body.
Large-scale studies also back this up. A 30-year study tracking over 200,000 people in the US found that higher intake of plant oils, including seed oils, was linked to a lower risk of death from cardiovascular disease and cancer. Conversely, those who consumed more butter were more likely to die during the study period.
One omega-6 fatty acid in particular, linoleic acid, has shown heart-health benefits. Research led by Matti Marklund at Johns Hopkins University found that people with higher levels of linoleic acid in their blood were significantly less likely to develop cardiovascular disease.
Some experts have warned about the imbalance between omega-6 and omega-3 in modern diets. Western diets often feature a ratio of up to 50:1, while a 4:1 ratio is considered more ideal. However, Marklund cautions against reducing omega-6 intake and instead encourages people to increase their omega-3 consumption, as both types are essential and beneficial.
Another concern involves the industrial processing of seed oils. While some oils are extracted using hexane, a chemical solvent, scientists say this is standard in food processing and that further refining removes any harmful residues. Cold-pressed alternatives avoid chemical use but are more expensive.
One recent study did link omega-6 consumption to tumour growth in a specific type of breast cancer, but researchers stress this doesn’t apply broadly. “Omega-6 fats are essential for a reason,” said lead researcher Kostas Koundouros. “Eliminating them entirely could have serious health consequences.”
Among seed oils, canola and soybean oil have the strongest evidence base and offer a healthy balance of fats. Mozaffarian even noted that canola oil may improve cholesterol more effectively than olive oil.
In summary, while more high-quality research is needed, current evidence suggests that seed oils, in moderation, are not harmful — and may in fact offer significant health benefits.
