Are Seed Oils Bad For You?

I vividly remember Spring of 2022: I was nearing completion of my PGY1 residency, considering signing up for my first marathon, and deep in the grasp of fitness influencers. Ironically, the fitness influencer I was most obsessed with at the time is one I no longer follow.

This influencer (and supplement company owner) was preaching about the harms of seed oils. Naturally, I was then brainwashed into thinking I, too, needed to banish seed oils from my diet. I lasted about 3 weeks. During those three weeks, I loved the challenge of finding meals and snacks that did not list any seed oils on the ingredient label. Did I notice a difference in my body and mood? Of course. Was this solely based on the omission of seed oils from my diet? Absolutely not.

I will explain why I made this conclusion as we dive into this topic. We first need to discuss what seed oils are, how common seed oils are in the food we consume, and what contributed to my improved body image and mood during my short, 3-week experiment.

What are Seed Oils?

Seed oils are made from a variety of seeds and plants. They are often used in everyday cooking and ultra-processed foods. Although seed oils are plant-based in nature, they are made through chemical processes which include bleaching, refining, and heating.

These processes remove healthy antioxidants like vitamin E and phenols and leave behind omega-6 fatty acids (a type of polyunsaturated fat). You may be familiar with omega-3 fatty acids in fatty fish and fish oil supplements. Omega-3s are the "healthy polyunsaturated fats" that support cardiovascular health. That being said, omega-6s are not bad for you, but your body likes to keep omega-3s and -6s in homeostasis. The American diet, typically on the more processed side due in part to the inclusion of seed oils, can throw off this balance from the consumption of too many omega-6 fatty acids.

Dr. DiNicolantonio published a paper in 2021 detailing the specific ratios of omega-6/3 and how the ratio has changed over the last 100 years. Ideally, the ratio was about 4:1.² In more recent years, it has increased to 20:1.² He attributes the increase to the over-consumption of omega-6-rich seed oils.² The rest of his paper highlights the importance of maintaining a lower 6/3 ratio to reduce the risk of autoimmune disease, asthma, and allergies.²

"Tell me more about Omega-6"

Omega-6s are part of a healthy diet, in small amounts. They are found everywhere in the body and help with the function of all cells. Omega-6s and Omega-3s are also referred to as linoleic acid/alpha-linolenic acid.

I liked this explanation from the Encyclopedia of Food and Health (2016)³:

Cold-pressed olive oil and other vegetable oils such as sunflower have been reported to have a lower linoleic acid (LA)/alpha-linolenic acid ratio (ALA) [ratio] as compared with refined vegetable oils and a higher amount of oleic acid. Similarly, β-carotene was present in cold-pressed vegetable oils but is absent in the refined ones.

Hydrogenation of vegetable oils is a process used in order to produce semisolid or solid fats from vegetable oils. During the process of partial hydrogenation, trans-fatty acids (TFAs) are produced that have adverse health effects, and therefore, alternative methods of converting vegetable oils to solid fats have been introduced. Interesterification, that is, rearrangement of fatty acids within a triacylglycerol, is a process now widely used, although there are conflicting data regarding possible adverse health effects on lipoprotein and serum glucose metabolism and hemostasis parameters.

A few notes/explanations about this excerpt to understand before we move on:

• Oleic acid: omega-9 fatty acid that occurs naturally in animal and vegetable fats; may improve heart health and lower inflammation
• Hydrogenation: a chemical reaction that adds hydrogen to a liquid fat to increase shelf life and save cost. Known as "trans fat"

• Trans-fatty acids: an unsaturated fatty acid of a type occurring in margarines and manufactured cooking oils as a result of the hydrogenation process, having a trans arrangement of the carbon atoms adjacent to its double bonds. Consumption of such acids is thought to increase the risk of atherosclerosis. (Oxford Languages definition)

The Science of Linoleic Acid (Omega-6)

Because it was known that linoleic acid (LA) reduces blood cholesterol levels and lowers the risk of heart disease, the American Heart Association (AHA) Science Advisory recommended in 2009 that omega-6 polyunsaturated fatty acids make up at least 5 to 10% of total energy.^4,5 The American Dietetic Association and Dietitians of Canada published the same recommendation earlier than the AHA in 2007.⁶

Despite major, reputable sources recommending a daily intake of LA, the possibility of LA leading to excess inflammation could not be ignored. The science of consuming an excess of LA is thought to "prompt excessive formation of arachidonic acid (AA) and subsequent synthesis of pro-inflammatory eicosanoids (e.g., prostaglandin E₂, leukotriene B₄, and thromboxane A₄). Elevated pro-inflammatory eicosanoid generation could drive up other biomarkers of inflammation (e.g., interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), C-reactive protein (CRP)) that are associated with increased incidence of CVD, cancer," inflammation, swelling, irritation, autoimmune diseases, and irritable bowel disease.⁵

Several published studies looked at the relationship between LA intake and inflammation in humans, yet no clear association was found.^7-10 One randomized crossover trial of 15 normal-weight males published in 2024 found that a 5-day high-fat diet enriched with cottonseed oil reduced TNF-alpha and tissue factor more than an olive oil-enriched diet.¹¹ When evaluating conjugated linolic acid supplementation, results are often mixed, showing reductions in some inflammatory markers (TNF-alpha, IL-6) and increases in others (CRP).^12,13

The "Hateful Eight" of Seed Oils

So what oils fall under the umbrella term of "seed oils"? Here is a well-known list from several sources:

• Canola oil (aka rapeseed oil)
• Corn oil
• Cottonseed
• Grapeseed oil
• Soybean oil
• Sunflower oil
• Safflower oil
• Rice bran oil
• (Peanut oil - the ninth seed oil of concern in many articles)

The Real Reason Seed Oils Have a Bad Reputation

We have already mentioned that seed oils are primarily found in ultra-processed foods, right? And that seed oils in small amounts can be healthy and unharmful. Let's consider the two meals below:

1. Meal option 1: Roasted vegetables and potatoes in olive oil with seasonings. Pan-fried chicken breast with a bit of butter. Dinner rolls on the side.
2. Meal option 2: Boxed mac 'n cheese. Chicken nuggets baked in the oven. Single-serving bag of chips. A can of Coke.

These two meal options are drastically different. The first uses olive oil and butter. The second doesn't appear to use any oil or fats. However, looking closer at meal option 2....

You can see the highlighted ingredients for the items in meal option 2. There are hidden seed oils in 3/4 items (not to mention the other laundry list of ingredients in each product! Like high fructose corn syrup in the Coke! – not pictured).

It would be easy to turn Meal 1 into a seed oil massacre, too. If the preparer did not have olive oil or butter but opted to use canola oil for the roasted vegetables and pan-fried chicken, well then the health benefits of all the whole foods included in this meal might be partially counteracted with the inclusion of a seed oil (depending on the quantity).

I recognize there are limitations for some individuals and families between the two meal options. The second option might be easier for a college student living in a dorm, low-income families, and more kid-friendly. This example is pretty drastic, but eye-opening, nonetheless. The main point I am making here is seed oils take the blame for being unhealthy when in reality the frequent consumption of processed foods is to blame. Making conscious decisions to limit seed oils will ultimately lead to limiting processed foods entirely.

From my 3-week experiment, I was still able to find certain snacks/bars/chips that did not include a seed oil on the label but had other hard-to-pronounce-chemical compounds in the ingredient list. So no, I was not solely eating whole, unprocessed foods at the time. However, when trying to limit just seed oils, I found myself choosing to buy a RxBar and grapes at the airport, seeking out more whole-ingredient bars and baked crackers instead of candy bars and traditional bagged chips. For me, limiting seed oils cleaned up my diet for 3 weeks. No wonder I felt great and perceived my body as "less inflamed." Little changes can go a long way, and you do not have to drastically change your diet to Whole30 or vegan to see benefits.

"What Oils Should I Use?"

I want to first say that if your diet contains seed oils, whether from cooking oil or a few of your favorite processed snacks, do not worry. From the data currently available, moderate consumption of omega-6s does not seem to have a direct correlation (that we know of) with inflammation. The caveat to my statement here is that hopefully your diet contains an adequate portion of omega-3s as well, as the literature does support a healthy balance of these two components. For myself, I have added in a fish oil supplement (Nature's Bounty brand because that is what Costco carries) to ensure I am hitting my omega-3 quota. This is by no means necessary, but I feel better by taking it nightly.

If you would like to be more conscious about your seed oil consumption, other alternatives include:

• Olive oil
• Extra virgin olive oil
• Avocado oil
• Coconut oil

A big component of cooking oil selection that I did not consider until I met my husband is the smoke point and the purpose of each type of oil. This topic could be another post in itself. I will leave you with this blog post on the different types of cooking oils from MBG Food, reviewed by Lauren Torrisi-Gorra, M.S., RD.

Final Thoughts and Conclusions

Here is my final hit list from the wealth of information presented above:

• Do not believe everything you see online from "fitness influencers," no matter how big of a following they have.
• Seed oils, in moderation, can be a part of a healthy diet.
• Take a quick look at the past week of your eating habits: does your diet consist of primarily processed, pre-packaged foods? If yes, consider switching out a few of your staples for less-processed, whole-ingredient alternatives.
• Next time you are at the store, pick up a bottle of avocado or coconut oil to replace the vegetable/canola oil in your cabinet that you typically use for sauteeing/roasting.
• Omega-6 fatty acids have not been shown to directly increase inflammatory markers, but the quality of evidence available in the literature is a limitation at this time.
• Consider a fish oil supplement if you feel you may not be obtaining enough omega-3 fatty acids from your diet.
• Oh, not mentioned, but implied: stay active, get those daily steps in, and soak up some vitamin D (sunshine)! Diet is only half the battle to a healthy, long life and inflammation management. Moving your body and circulating blood flow is a crucial part, too!

*Information presented on RxTeach does not represent the opinion of any specific company, organization, or team other than the authors themselves. No patient-provider relationship is created.

References

1. Seed Oils: Are They Actually Toxic? Cleveland Clinic, 2023. https://health.clevelandclinic.org/seed-oils-are-they-actually-toxic
2. DiNicolantonio, J. J. (2021). The Importance of Maintaining a Low Omega-6/Omega-3 Ratio for Reducing the Risk of Autoimmune Diseases, Asthma, and Allergies. Missouri Medicine, 118(5), 453-459. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8504498/
3. S.C. Savva, A. Kafatos,Vegetable Oils: Dietary Importance,
   Editor(s): Benjamin Caballero, Paul M. Finglas, Fidel Toldrá,
   Encyclopedia of Food and Health,Academic Press,2016,Pages 365-372, ISBN 9780123849533.
4. Harris WS, Mozaffarian D, Rimm E, Kris-Etherton P, Rudel LL, Appel LJ, Engler MM, Engler MB, Sacks F. Omega-6 fatty acids and risk for cardiovascular disease: A science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009;119(6):902–907.
5. Fritsche KL. Linoleic acid, vegetable oils & inflammation. Mo Med. 2014 Jan-Feb;111(1):41-3. PMID: 24645297; PMCID: PMC6179509.
6. Kris-Etherton PM, Innis S American Dietetic Association, Dietitians of Canada. Position of the American Dietetic Association and Dietitiansof Canada: Dietary fatty acids. J Am Diet Assoc. 2007;107(9):1599–1611.
7. Ferrucci L, Cherubini A, Bandinelli S, Bartali B, Corsi A, Laurentani F, Martin A, Andres-Lacueva C, Senin U, Guralnik JM. Relationship of plasma polyunsaturated fatty acids to circulating inflammatory markers. J Clin Endocrinol Metab. 2006;91:439–446.
8. Pischon T, Hankinson SE, Hotamisligil GS, Rifai N, Willett WC, Rimm EB. Habitual dietary intake of n-3 and n-6 fatty acids in relation to inflammatory markers among US men and women. Circulation. 2003;108:155–160.
9. Fernandez-Real JM, Broch M, Vendrell J, Ricart W. Insulin resistance, inflammation, and serum fatty acid composition. Diabetes Care. 2003;26:1362–1368.
10. Klein-Platat C, Drai J, Oujaa M, Schlienger JL, Simon C. Plasma fatty acid composition is associated with the metabolic syndrome and low-grade inflammation in overweight adolescents. Am J Clin Nutr. 2005;82:1178–1184.
11. Catherine Prater M, Polley KR, Cooper JA. Improvements in markers of inflammation and coagulation potential following a 5-day high-fat diet rich in cottonseed oil vs. Olive oil in healthy males. Cytokine. 2024 Mar;175:156494. doi: 10.1016/j.cyto.2023.156494. Epub 2024 Jan 3. PMID: 38171039.
12. Rastgoo S, Shimi G, Shiraseb F, Karbasi A, Ashtary-Larky D, Yousefi M, Golalipour E, Asbaghi O, Zamani M. The effects of conjugated linoleic acid supplementation on inflammatory cytokines and adipokines in adults: A GRADE-assessed systematic review and dose-response meta-analysis. Front Immunol. 2023 Feb 22;14:1092077. doi: 10.3389/fimmu.2023.1092077. PMID: 36911696; PMCID: PMC9992184.
13. Haghighatdoost F, Nobakht M Gh BF. Effect of conjugated linoleic acid on blood inflammatory markers: a systematic review and meta-analysis on randomized controlled trials. Eur J Clin Nutr. 2018 Aug;72(8):1071-1082. doi: 10.1038/s41430-017-0048-z. Epub 2017 Dec 29. PMID: 29288248.