How Seed Oils Were Demonized
A sketchy conjectural hypothesis was transmogrified into a dubious dietary dogma.
The controversy over polyunsaturated seed oils is in some respects the mirror image of the fight over saturated fats in meat, milk, and eggs. Omega-3 and omega-6 fatty acids are essential fatty acids. They are "essential" since they must be provided by foods because they cannot be synthesized in the body yet are necessary for health. Both act as structural components in cellular membranes and modulate inflammatory responses.
The three main omega-3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The principal sources of omega-3 fatty acids are oily fish, flaxseed oil, and nuts like walnuts. The chief omega-6 fatty acid is linoleic acid. The prime sources of linoleic acid in modern diets are seed oils including soybean, corn, cottonseed, sunflower, canola, safflower, rice bran, and grapeseed oils. The use of these oils has increased in modern diets, and they have been dubbed by some self-proclaimed health and wellness gurus as the "hateful eight."
The main contention by these health gurus is that the modern dietary "balance" between omega-3 and omega-6 essential fatty acids is out of whack, resulting in a host of alleged bad effects on health. For decades, American physician and endocrinologist Artemis Simopoulos has been one of the chief proponents that a present-day imbalance between omega-3 and omega-6 fatty acids in the contemporary diet is the source of many modern ills. Simopoulos appears to have first encountered this hypothesis while attending the 1988 NATO Advanced Research Workshop on Dietary Omega-3 and Omega-6 Fatty Acids in Italy.
Simopoulos became the co-editor of the proceedings volume for that conference, publishing a paper that suggested that the optimal ratio for intakes of omega-3 and omega-6 fatty acids was 1 to 5-6 based on a 1985 study in which a team of French researchers fed 24 nuns different proportions of the two nutrients for five months published in Lipids. The proceedings volume also noted that "the current estimate of this ratio in the western diet is 10-11/1. Evidence based on estimates from paleolithic nutrition and from terrestrial animals (mammals) in the wild indicate a ratio of omega-6 to omega-3 to be 1 to 1 in the diet."
An earlier 1988 summary of that same conference in the Journal of the American Oil Chemists' Society noted that "some conference participants felt that the dietary ratio of omega-6 to omega-3 fatty acids of about four-to-one might be desirable." In her 1989 summary article in the Journal of Nutrition, Simopoulos cited the paleolithic ratio estimate but also reported that conference "participants could not agree on either a recommendation for omega-3 fatty acid intake as a percent of dietary calories or on the ratio of omega-6 to omega-3 in the diet."
However, Simopoulos had made up her mind. In her 1991 review article in the American Journal of Clinical Nutrition, she again asserted that the recent big increase in the availability of seed oils had created evolutionarily suspect "imbalances between omega-6 and omega-3" fatty acids." Simopoulos suggested that this "imbalance" significantly contributed to coronary artery disease, inflammatory disorders, and cancer. She later popularized her theories about the alleged ill effects of increased seed oil consumption in her co-authored 1997 diet book, The Omega Plan: The Medically Proven Diet That Restores Your Body's Essential Nutritional Balance. In the book, she asserted that the "hidden imbalance" between omega-6 and omega-3 fatty acids "makes you more vulnerable to heart disease, cancer, obesity, inflammations, autoimmune diseases, allergies, diabetes and depression—all of the so-called diseases of civilization."
It is worth noting that exercise physiologist and chief originator of the paleo diet, Loren Cordain, participated in a number of nutrition and fitness conferences overseen by Simopoulos in the 1990s. For example, he was one of the promulgators of the 1996 Declaration of Olympia on Nutrition and Fitness that among other things recommended that "nutrient intakes should more closely match human evolutionary heritage," specifically mentioning the role of "essential fatty acids."
In 1997, Cordain was co-author of an article on evolutionary aspects of diet in World Review of Nutrition and Dietetics edited by Simopoulus in which they observed, "The ratio of omega-6 to omega-3 PUFA (polyunsaturated fatty acids) is estimated to have been far lower for preagricultural humans than for Americans." He and his co-author then speculated that this higher ratio of omega-6 to omega-3 fatty acids "may have important physiological consequences." The authors modestly concluded, "Paleonutrition is an intellectually appealing, but unproved, dietary paradigm."
In 1998, Cordain was a co-author of an article focused on fatty acids during the Paleolithic that was published in the World Review of Nutrition and Dietetics, again edited by Simopoulos. While noting that "evolutionary considerations are not (yet) a basis upon which to make nutritional recommendations," Cordain and his co-authors nevertheless went on to observe that with respect to essential fatty acids, "current intake clearly differs from that of our ancestors: preagricultural humans generally consumed omega-6 and omega-3 PUFA [polyunsaturated fatty acids] in roughly equal amounts." Cordain and his co-authors then added, "This pattern fueled the emergence and development of our genus; evolutionary considerations commend its restoration."
And "commend its restoration" Cordain certainly did in his 2002 blockbuster The Paleo Diet. There Cordain endorsed Simopoulos' claims about the health harms of "imbalanced" omega fatty acids. He asserted that "the ratio of omega-6 to omega-3 fats in Paleo diets was about 2 to 1; for the average American, the ratio is much too high—about 10 to 1. Eating too many omega-6 fats instead of omega-3 fats increases your risk of heart disease and certain forms of cancer; it also aggravates inflammatory and autoimmune diseases."
For what it's worth, a 2018 study in Lipids In Health and Disease confirms the modern ratio of fatty acids in the modern American diet when it reported that the omega-6 to omega-3 ratio for U.S children and older adults averages 9 to 1, and 8 to 1 respectively.
Keep firmly in mind that with respect to the problematic subject of nutritional epidemiology, no prior claims about the harms or benefits of any nutrient ever fully disappear. For example, alternative medicine proponent Joseph Mercola is a co-author of the 2023 narrative review in Nutrients that outlines research that purports to demonstrate the deleterious health effects of consuming linoleic acid.
However, as you will see in the main article, the bulk of recent research has not been kind to Simopoulos' assertion that the supposedly imbalanced consumption of linoleic acid found in seed oils "makes you more vulnerable to heart disease, cancer, obesity, inflammations, autoimmune diseases, allergies, diabetes and depression." On the contrary, most research finds that consuming seed oils reduces the risks of these maladies.
