Seed Oils: Facts & Myths

Seed oils have become a hot topic on social media, often sparking debate whether they’re health promoting or “toxic.” Many health influencers are suggesting the production methods and high omega-6 fatty acid composition of seed oils are to blame for a wide range of health issues from brain fog to chronic inflammation and obesity. But does research support these claims? Many nutrition experts and scientific studies advocate for a diet that includes the fatty acids found in seed oils, emphasizing the health benefits of replacing saturated fats in the diet with unsaturated fats. So, which is it?

What are seed oils?

Seed oils are cooking oils extracted from the seeds of various plants and commonly known as vegetable oils. The most common seed oils, referred to by social media wellness influencers as the “Hateful Eight,” include:

• Canola (rapeseed) oil
• Corn oil
• Cottonseed oil
• Soybean oil
• Sunflower oil
• Safflower oil
• Grapeseed oil
• Rice Bran oils

How are seed oils produced?

The seed oils are extracted from plants either by a chemical or mechanical process. Seed oil critics claim the chemical extraction process leaves toxic byproducts, such as hexane, in the oils. While hexane is considered hazardous in gas form, it’s used as a liquid solvent to extract the oil from the seeds. The hexane is then evaporated off. Since the FDA does not currently monitor or regulate hexane residue in cooking oils, it’s unclear what trace amounts of hexane, if any, remain in the seed oils found on the supermarket shelves.

Alternatively, oils can be mechanically extracted through cold pressing or expeller pressing of the plant seeds. While there are no chemical solvents in this process, these oils tend to have lower smoke points for cooking, shorter shelf lives, and are more expensive because they are unrefined.

What about the omega-6s?

All dietary fat sources are a mix of saturated, monounsaturated (MUFAs), and polyunsaturated fatty acids (PUFAs). Polyunsaturated fats also include omega-3s and omega-6s, and critics of seed oils propose that the omega-6 fatty acids found in seed oils are the cause of chronic inflammation. The reasoning is that linoleic acid, the most common omega-6, is converted into arachidonic acid in the body, which is a building block for compounds that cause inflammation. While this may sound convincing, a 2017 meta-analysis of randomized control trials found that increased dietary intake of linoleic acid does not have a significant effect on blood concentrations of inflammatory markers. This is likely because only a small percentage, about 0.2%, of omega-6s is converted to arachidonic acid.

What many anti-seed oil influencers also overlook is that arachidonic acid is also a precursor for compounds that fight inflammation in the body. Many studies, including 2023 research in the International Journal of Molecular Sciences, show a higher intake of omega-6 fatty acids is associated with better cardiovascular health and improved glucose metabolism. The American Heart Association also supports the inclusion of omega-6s as part of a healthy diet to prevent cardiovascular disease.

Concerns have also been raised over the ratio of omega-6 to omega-3 fatty acids in the diet. The claim is that historically, humans consumed a diet with a 1:1 ratio of omega-6s to omega-3s, while the standard American diet has increased this ratio to 10:1 or greater. There is no denying the widely accepted health benefits of omega-3 fatty acids found in fatty fish, walnuts, and flaxseeds, but the ideal ratio of fatty acids remains somewhat unclear.

Can seed oils be part of a healthy diet?

It’s important to consider the context of how seed oils and their omega-6s make it to consumers’ mouths. Most are used in deep-fried foods, fast food, and packaged snacks. These ultra-processed foods also tend to be high in sodium, refined carbohydrates, and added sugars, providing little nutritional benefit. Replacing ultra-processed food choices with more minimally processed whole foods such as fruits, vegetables, lean proteins, whole grains, legumes, nuts, and seeds is a more constructive tactic than aiming to eliminate seed oils entirely from one’s diet. Seed oils can be a beneficial part of a healthy diet when used in cooking, such as in stir frying vegetables, oven roasting fish, or crafting homemade salad dressings.