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Seed Oils: Facts and Fallacies

  • Writer: FibonacciMD
    FibonacciMD
  • 12 hours ago
  • 7 min read

Updated: 10 hours ago

Are seed oils truly "toxic" or a heart-healthy staple? Explore the science behind omega-6 fatty acids, inflammation, and the impact of ultra-processed foods on chronic disease.

Culinary Medicine


seed oils facts and fallacies
photo by Mary Grosvenor

 by  Lori A Smolin, PhD  and


Seed oils are a hot topic of debate. These oils, extracted from the seeds of plants such as corn, soy, canola, safflower, and sunflower, are among the most widely used oils in homes, restaurants, and processed foods. Online influencers argue that the types of fatty acids they contain promote inflammation and that our increased consumption of seed oils is responsible for our expanding rates of chronic diseases such as obesity and heart disease.[1] In addition they suggest that the way these oils are processed introduces toxins into our diet.


However, major scientific and health organizations recommend choosing plant-based oils, including seed oils, as part of a healthy diet. Should we avoid seed oils? 


The ABCs and Health Impact of Fats and Oils  

Fats and oils are made up of mixtures of fatty acids. Saturated fatty acids are found primarily in animal foods such as meat and dairy products. A high intake of saturated fatty acids contributes to cardiovascular disease by raising blood cholesterol levels.[2] Research has repeatedly shown that cardiovascular disease risk is significantly reduced when saturated fats are replaced by unsaturated fats.[3] Unsaturated fats include mono- and polyunsaturated fats. Monounsaturated fatty acids are found in olive, canola, and avocado oils. Diets high in monounsaturated fatty acids have been shown to reduce the risk of heart disease.[4] Polyunsaturated fatty acids include omega-3 and omega-6 fatty acids, which are dietary essentials.


Good sources of omega-3s include nuts, seeds, fish, and beans. Omega-6s are also found in nuts and seeds as well as seed oils. In the body, omega-3 and omega-6 fatty acids compete for pathways that form regulatory molecules that affect levels of inflammation and other metabolic processes, such as blood clotting and blood pressure. The type of regulatory molecule formed depends on the starting material. For example, if the starting material is the omega-3 fatty acid alpha-linolenic acid, the resulting molecule can decrease inflammation. And if the starting material is the omega-6 fatty acid linoleic acid, the resulting molecule can increase inflammation.  


Do Seed Oils Contribute to Chronic Inflammation?  

Inflammation is an essential component of our immune response. In the short term, inflammation helps eliminate harmful substances and initiate healing, but persistent, unresolved inflammation, referred to as chronic inflammation, contributes to the risk for chronic diseases. Studies have identified a number of factors that might promote chronic inflammation.[5,6] One of these is a high ratio of dietary omega-6 to omega-3 fatty acids.[7,8] Since seed oils are generally higher in omega-6 than omega-3 fatty acids, their use has been proposed as a cause of inflammation. [9] However, this hypothesis is not well supported.


Human studies have found that an increased intake of omega-6 fatty acids does not increase in blood concentrations of most inflammatory markers.[10,11] And, epidemiological studies have found little relationship between the omega-6 to omega-3 ratio in the diet or the blood and the risk of cardiovascular disease.[6] The likely reason this hypothesis is not supported is that it considers only pro-inflammatory omega-6 fatty acid metabolites. It does not consider anti-inflammatory omega-6 fatty acid metabolites or other factors that affect levels of inflammation and the risk of chronic disease. [6] Aging, stress, lack of exercise, and a diet high in ultra-processed foods are risk factors for chronic inflammation.[5]


Does the Processing of Seed Oils Introduce Risk? 

The potential negative health effects of seed oils have also been attributed to the refining process. Seed oils are most often produced by chemically extracting the oil from the seeds using the solvent hexane. Hexane is known to cause central nervous system symptoms such as muscle weakness and numbness when it is inhaled, but the effects of ingestion are not fully understood.[12] Most of the hexane used in extracting oils evaporates but traces may remain in the oils. Critics of seed oils claim that this residual hexane is a hazard to health. Currently, the FDA does not monitor residual hexane in seed oils but considers the levels too low to have any effect on human health.[13] If you are concerned that hexane is a health hazard, you can avoid it by choosing organic, expeller-pressed, cold-pressed, or unrefined seed oils.[14]


Has the Rise in Seed Oil Consumption Contributed to Chronic Disease? 

The rise in seed oil consumption has paralleled increases in obesity and other diet-related chronic diseases, but association does not mean causation.[15] Advances in food technology in the early 20th century allowed for the mass production of neutral flavored, heat-stable vegetable oils, including seed oils. [16] The wide availability of these inexpensive oils high in polyunsaturated fats has significantly increased our intake of omega-6 fatty acids.[8,17] But neither the oils themselves nor the omega-6 fatty acids they contain are likely to be the cause of the rising rates of chronic diseases in the United States.[18]


Seed oils are abundant in ultra-processed foods such as chips, cookies, and snack bars, which now provide more than half of the calories consumed at home by U.S. adults.[19] These foods are high in calories, refined carbohydrates, added sugars, and salt and excessive intake is recognized as a risk factor for diet-related diseases.[20] Therefore, ultra-processed foods are a more likely contributor to the increased incidence of chronic disease than the seed oils they contain.[15,17] 


Bottom Line  

 Simply stated, there is no conclusive evidence that seed oils increase health risks. There is evidence that replacing saturated fats with unsaturated fats, including those in seed oils, reduces the risk of cardiovascular disease. [6]


To optimize the benefits of unsaturated fats, it is best to include a variety of them in your food choices. Most of us get more than enough omega-6 fatty acids in our diets. To up your omega-3s, eat more fish, walnuts, and seeds such as pumpkin, sunflower, flax, and chia seeds.  To increase your monounsaturated fat intake, choose olive, canola, and avocado oil for cooking and sauces. You can further increase the overall healthfulness of your diet by limiting ultra-processed foods and basing your meals and snacks on whole and minimally processed foods.


Mary Recommends

As an Amazon Associate FibonacciMD earns from qualifying purchases.


A heart-healthy kitchen staple, La Tourangelle Organic Canola Oil is an expeller-pressed, non-GMO oil with a neutral flavor and high smoke point—ideal for all your everyday sautéing and frying. [https://amzn.to/4aztf7p]


Not a seed oil, but a great heart-healthy alternative, La Tourangelle’s Sear & Sizzle Avocado Oil is a handcrafted, high-smoke point oil.[https://amzn.to/4qQCuF3]


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