Production and widespread consumption of seed oils in the U.S. began in the early 20th century. Given the popularity and cost-effectiveness of seed oils, it's likely you are consuming them on a regular basis in products such as salad dressing, packaged snacks, and fast food. You might even have a bottle of canola oil or sunflower oil on hand at home for cooking!
So, Why are seed oils so bad for you? And why are so many scientists and health experts recommending people stop consuming them?
What Are Seed Oils?
Seed oil is an edible oil derived from plant seeds. It may also be chemically processed or pressed from whole seeds. These include sesame seed oil, corn oil, cottonseed oil, soybean oil, sunflower oil, safflower oil, grapeseed oil, and rice bran oil.
Industrial seed oil production requires a rigorous process involving high temperatures, chemical extraction, and synthetic additives. What remains is a nutrient-deficient product that has been oxidized, likely contains trans fats, and is loaded with harmful chemicals such as TBHQ, BHA and BHT - all known to be carcinogenic. The refining process also removes nutrients like vitamin E, beta carotene, and omega 3 fatty acids. As a result, industrial seed oils lack essential vitamins and minerals. When all is said and done, seed oils provide very little health benefits compared to alternatives such as coconut oil or extra virgin olive oil.
It's important to understand that seed oil is a polyunsaturated fat (PUFA), meaning it has two or more double bonds in its chemical structure. This makes it incredibly unstable and prone to oxidation and rancidity.
Why Are Seed Oils Bad For you?
Oxidation occurs when fatty acids react to oxygen and begin to deteriorate. The result of degradation includes trans fat - a contributor to heart disease and type 2 diabetes - and lipid peroxides - a harmful byproduct that effects DNA, proteins, membrane lipids, and contributes to chronic disease.
Moreover, seed oils contain toxic chemicals called phytosterols, which are known to increase cholesterol levels and contribute to cardiovascular diseases. Phytosterol content varies widely among different types of seed oils, but they're present in most.
While some seed oil varieties are known for having a high smoking point (the temperature at which they begin to burn, typically 400°F and higher), it's not uncommon for restaurants to heat these types of oil over their smoke point repeatedly. This practice has been known to develop carcinogenic compounds and free radicals.
Finally, because these oils contain large amounts of omega-6 fatty acids (a precursor to inflammation), they contribute to inflammatory conditions and chronic illness like arthritis, asthma, eczema, psoriasis, and other autoimmune diseases. Omega-6 fats are essential for our health, but we need them in small quantities and from high-quality sources, such as avocados, walnuts, salmon, eggs, and chicken.
Just like the case of refined sugars, the human body has not evolved to eat large amounts of linoleic acid (the main fatty acid found in seeds). Studies have shown that consumption of linoleic acids may have pro-inflammatory and thrombrogenic properties.
List of Seed Oils to Avoid
Rice bran oil