There are many things that can go wrong with sunflower oil – “Depending on how it is processed and its fatty acid profile, it can be extremely unhealthy and contribute to significant metabolic dysfunction,” says Shanahan. As mentioned above, you should really avoid varieties of refined sunflower oil that are also high in linoleic acid, an omega-6 PUFA that is quite volatile.
There is nothing inherently wrong with omega-6 PUFAs, but the damage caused by exposure to high temperatures during refining and re-cooking is a major problem. “When these volatile PUFAs are exposed to high temperatures, they are chemically oxidized and chemically break down to form dangerous new molecules such as aldehydes, 4-hydroxynonal, cyclic amines, toxic alcohols and toxic ketones,” Shanahan said. When ingested, this collection of compounds can trigger oxidative stress and inflammation in the body and contribute to inflammatory conditions in a variety of chronic diseases ranging from joint pain to acne to intestinal problems.
But if high-PUFA oils like sunflower oil can make such a nasty cocktail of heated compounds, you might wonder why it is marketed as having high smoke point. Contrary to popular belief, an oil smoke point does not always guarantee stability under heat. In fact, various studies (like this) show that after repeated frying sessions, high-linoleic oils (smoke point 450 degrees Fahrenheit) are more harmful than sunflower oils, such as olive oil. Oil (smoke point 350 to 470 F). If you really want to cook with sunflower oil, high-oleic varieties are a more stable choice.
Finally, if you eat lots of PUFA-rich oils such as sunflower oil (and other common vegetable and seed oils), they can accumulate in your body fat. The problem, Shanahan explains, is that when your body burns these fats for fuel later, they break down – again – into the same dangerous compounds mentioned above, leading to further inflammation and overall metabolic dysfunction. Remember, you can inadvertently consume these oils when eating packaged foods — so read those labels and generally aim to eat more whole foods.