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Do seed oils cause inflammation?
Among all the food misinformation online, seed oils, in particular, have been the subject of controversy, with many labelling them as the culprits for inflammation and disease.
The sheer volume of information about seed oils online is immense. There are even accounts and apps dedicated to helping people avoid restaurants and products that contain seed oils.
Is this level of fear around seed oils valid? Can they really be so damaging to your health?
When we look at the evidence, it seems that the villainising of seed oils might just be one big misunderstanding…
Most of the trials done in humans show seed oils have no effects on a range of inflammatory biomarkers. Some studies even show they could have an anti-inflammatory effect.
Seed oils, extracted from plants like sunflower, soybean, and corn, have become a common ingredient in many diets due to their versatility and affordability. However, they’re now at the center of debate, with some claiming that seed oils contribute to inflammation and adverse health outcomes.
This is largely due to their high omega-6 fatty acid content. Specifically, critics argue that linoleic acid, an omega-6 found in high amounts in seed oils, may promote inflammation by increasing levels of another omega-6 fatty acid, arachidonic acid, in the body.
In the human body, linoleic acid is converted, via a multistep pathway, into another omega-6 fatty acid called arachidonic acid, which is involved in pro-inflammatory responses. So, by this understanding, more linoleic acid in the diet (through more seed oils) increases arachidonic acid and results in more inflammation.
However, evidence shows us this is not how it actually works in the body.
A systematic review looked at the results in 36 human intervention studies on whether more linoleic acid in the diet resulted in more arachidonic acid.
It did not.
Increasing the levels of linoleic acid by up to 551% did not significantly increase the levels of arachidonic acid in the plasma, serum, and red blood cells.
But what if you measure the levels of inflammation in the body after regular consumption of seed oils? Surely, given all the hype around their inflammatory effects, there would be strong evidence for this?
Not quite.
Studies have also debunked the prevailing myth that these oils lead to inflammation, showing that they may actually possess anti-inflammatory properties. Yes, you read that right—anti-inflammatory!
“Seed oils contain omega-6 fatty acids. Some argue that too many of these fatty acids are pro-inflammatory, but the research doesn't support that at all. This review of dozens of control studies looked at 10 on the effect of seed oils on inflammatory markers. They found that not a single study found convincing evidence that seed oils increase inflammation, and actually, three of them found seed oils to have an anti-inflammatory effect.” says Dr Idz.
This review failed to find substantial evidence linking seed oils to increased inflammation.
Another systematic review of 15 randomised controlled trials in healthy humans found no significant evidence for dietary linoleic acid increasing a range of inflammatory markers.
The evidence supporting the claims that seed oils cause inflammation is next to zero. Including omega-6 fatty acids from seed oils in your diet is unlikely to spike your risk of disease or premature death.
When thinking about seed oils, which are high in omega-6 fatty acids, the concern is not actually about the consumption of the seed oils themselves, but rather the rampant imbalance and inadequate intake of omega-3 fatty acid consumption as compared to omega-6 fatty acid consumption. Omega-3 fatty acids are found within fatty fish such as tuna, salmon, and mackerel as well as plant sources such as flaxseeds, chia seeds, and walnuts. It is generally known that the standard American diet is inadequate in the consumption of these dietary sources of omega- 3 rich foods. This, in turn, produces an imbalance of the suggested omega-3: omega-6 fatty acid ratio, which may contribute to perpetuating bodily inflammatory responses. In fact, the American diet contains approximately 15-25 times more omega-6 fatty acids as compared to omega-3 fatty acids, producing ratios ranging from 14:1-25:1. The actual suggested omega-6: omega-3 ratios, which have been studied in helping to optimize and combat inflammatory processes is approximately 4:1 (omega-6: omega-3), and ideally 1:1.
If you consumed a diet high in seed oils contained within high-fat, high-sugar processed foods, you would likely see some adverse effects on your health. However, the current evidence from controlled human trials suggests that seed oils in isolation do not cause inflammation in the body.
“The key isn't to fear seed oils, but to embrace a diet rich in whole foods. For example, fruits, veggies, pulses, and whole grains. These are your champions in fighting inflammation and disease. Overall, the science suggests that having omega-6 fatty acids from seed oils in your diet is unlikely to increase your risk of death or disease.
Remember, no single food is ever the enemy, it’s about the diet overall.
If you want a deeper dive into the topic, take a look at this video by Nutrition Made Simple.
Top Nutrition Coaching is a platform offering personalised nutrition plans tailored by registered dieticians (RDs).
Sources
Innes, J, et al. (2018). Omega-6 fatty acids and inflammation. https://pubmed.ncbi.nlm.nih.gov/29610056/.
Johnson, G,et al. (2012). Effect of Dietary Linoleic Acid on Markers of Inflammation in Healthy Persons: A Systematic Review of Randomized Controlled Trials. https://www.sciencedirect.com/science/article/abs/pii/S2212267212004649.
Rett, B, et al. (2011). Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review. https://pubmed.ncbi.nlm.nih.gov/21663641/.
Telle-Hanson et al. (2017). Does dietary fat affect inflammatory markers in overweight and obese individuals?—a review of randomized controlled trials from 2010 to 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC5628471/.
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