The debate over seed oils and their impact on health has sparked heated discussions in wellness circles, with linoleic acid (LA), an omega-6 fatty acid abundant in seed oils, at the centre of the controversy. Critics, including prominent alternative health advocates like Dr. Joseph Mercola, have long warned that high LA consumption, common in Western diets due to the prevalence of oils like soybean, corn, and sunflower, drives chronic inflammation, contributing to heart disease, obesity, and other modern health woes. Meanwhile, emerging research, such as a recent study published in Nutrients (Lai et al., 2025), suggests that higher LA levels may actually be associated with lower inflammation, challenging the anti-seed oil narrative. Adding fuel to the fire, some health gurus have recently raised concerns about excessive omega-3 intake, linking it to potential heart issues.
The vilification of seed oils stems from their high omega-6 content, particularly LA, which is an essential polyunsaturated fatty acid (PUFA). Seed oils, including canola, soybean, corn, and sunflower, became dietary staples in the 20th century due to their affordability, versatility, and widespread use in processed foods. However, critics argue that this shift led to a dramatic increase in omega-6 consumption, disrupting the balance between omega-6 and omega-3 fatty acids.
Historically, human diets maintained an omega-6 to omega-3 ratio close to 1:1 or 4:1. Today, Western diets often exhibit ratios as high as 20:1, driven by seed oil-heavy processed foods and low omega-3 intake from sources like fatty fish. Advocates like Dr. Mercola contend that this imbalance promotes chronic inflammation, as LA is metabolised into arachidonic acid (AA), which can produce pro-inflammatory molecules called eicosanoids. These molecules are implicated in conditions like cardiovascular disease, diabetes, and autoimmune disorders.
Dr. Mercola and others have pointed to observational studies and mechanistic arguments to support their claims. For example, some research suggests that high LA intake may increase oxidative stress, as PUFAs are prone to oxidation, potentially damaging cells and tissues. Critics also highlight the industrial processing of seed oils, which involves high heat and chemical solvents, potentially introducing harmful compounds like trans fats or oxidized lipids. These concerns have fuelled a broader movement to replace seed oils with alternatives like olive oil, coconut oil, or butter, which are lower in omega-6 or more stable during cooking.
The Counterargument: New Evidence Challenges the Narrative
Recent research, including the Nutrients study by Lai et al. (2025), paints a different picture. This large-scale, cross-sectional analysis from the Framingham Offspring Study examined blood levels of LA and AA in 2,700 participants, alongside 10 biomarkers of inflammation and oxidative stress. After adjusting for confounding factors like age, sex, smoking, and body weight, the researchers found that higher LA levels were associated with lower levels of five inflammation markers, with no evidence linking higher LA to increased inflammation. Similarly, higher AA levels correlated with reduced levels of four markers. These findings suggest that omega-6 fatty acids may have anti-inflammatory effects, directly contradicting the narrative that LA is inherently harmful.
Dr. William S. Harris, a co-author of the study, emphasised that these results align with a broader body of research. For instance, meta-analyses of randomised controlled trials (RCTs) have shown that replacing saturated fats with omega-6-rich oils can reduce cardiovascular risk, likely due to their ability to lower LDL cholesterol. The American Heart Association has endorsed this approach, citing evidence that omega-6 PUFAs are heart-protective when consumed in moderation.
Moreover, the idea that LA-driven eicosanoids are universally pro-inflammatory oversimplifies the biochemistry. While AA can produce pro-inflammatory molecules, it also generates anti-inflammatory compounds like lipoxins, which help resolve inflammation. The body's response to LA and AA depends on context, including genetics, overall diet, and lifestyle factors. For example, adequate omega-3 intake may modulate AA's effects, restoring balance to inflammatory pathways.
The Omega-3 Twist: Too Much of a Good Thing?
Adding complexity to the debate, some alternative health advocates, including Dr. Mercola, have recently cautioned against excessive omega-3 consumption. Omega-3 fatty acids, found in fish oil, flaxseed, and algae, are celebrated for their anti-inflammatory properties and cardiovascular benefits. However, concerns have emerged about potential risks, particularly related to heart rhythm disorders like atrial fibrillation.
A 2021 meta-analysis published in Circulation found that high-dose omega-3 supplements (e.g., 4 grams daily) were associated with a slightly increased risk of atrial fibrillation, particularly in patients with existing heart conditions. While omega-3s reduce triglycerides and inflammation, excessive doses may alter cardiac electrophysiology, potentially destabilising heart rhythms. Dr. Mercola has cited such findings to argue that the pendulum may have swung too far toward omega-3 supplementation, especially in the absence of dietary balance.
This critique aligns with the broader argument that nutrient imbalances, whether omega-6 or omega-3, are the real issue. The optimal approach, according to some experts, is to focus on whole foods (e.g., fatty fish for omega-3s, nuts for omega-6s) rather than relying on supplements or processed oils, which may lack the synergistic nutrients found in natural sources.
Navigating the Controversy: What Does the Science Say?
The seed oil controversy highlights the challenges of translating complex nutritional science into practical advice. Here are key points to consider:
1.Inflammation is Multifaceted: Inflammation is influenced by numerous factors, stress, sleep, exercise, and overall diet, not just omega-6 intake. The Nutrients study suggests that LA and AA are not inherently pro-inflammatory, but excessive consumption in an unbalanced diet may still pose risks.
2.Context Matters: The health effects of seed oils depend on how they're consumed. Oils used in deep-frying or ultra-processed foods may contribute to oxidative stress due to high heat or additives, whereas cold-pressed oils in moderation (e.g., in salad dressings) are less likely to be harmful.
3.Omega-6 to Omega-3 Ratio: While the ideal ratio remains debated, increasing omega-3 intake from sources like salmon or chia seeds can help balance high omega-6 levels without eliminating seed oils entirely.
4.Quality Over Quantity: Not all seed oils are equal. Highly processed oils may contain oxidised compounds, whereas minimally processed options like extra-virgin olive oil or cold-pressed sunflower oil retain more beneficial nutrients.
5.Individual Variability: Genetic factors, such as variations in the FADS1 gene, influence how efficiently individuals convert LA to AA. This means that some people may tolerate higher LA intakes better than others.
Practical Recommendations
Given the conflicting narratives, here's how to approach seed oils and fatty acid balance:
Prioritise Whole Foods: Incorporate omega-6 sources like nuts and seeds and omega-3 sources like fatty fish or flaxseeds into your diet. These foods provide additional nutrients, like antioxidants, that processed oils lack.
Choose High-Quality Oils: Opt for minimally processed oils (e.g., cold-pressed or extra-virgin) and avoid those used in high-heat cooking, which can degrade PUFAs and create harmful byproducts.
Balance Omega-3 and Omega-6: Aim to increase omega-3 intake through foods or moderate supplementation (e.g., 1–2 grams of fish oil daily) while being mindful of seed oil-heavy processed foods.
Stay Sceptical of Extremes: Be wary of blanket claims demonising or glorifying any single nutrient. Nutrition science is nuanced, and absolutes rarely hold up.
Consult Experts: If you have specific health conditions, consult a dietitian to tailor your fat intake to your needs, especially if you're at risk for heart disease.
In conclusion the seed oil controversy reflects a broader tension in nutrition: the desire for simple answers in a field rife with complexity. While alternative health advocates like Dr. Mercola raise valid concerns about dietary imbalances and processed foods, the latest evidence, including the Nutrients study, suggests that omega-6 fatty acids like LA are not the villains they're often made out to be. At the same time, emerging cautions about excessive omega-3 intake remind us that balance is key. By focusing on whole foods, high-quality oils, and a balanced omega-6 to omega-3 ratio, you can navigate this controversy without falling prey to fearmongering or oversimplification.
Reference: Lai, H. T. M., et al. (2025). Red Blood Cell Omega-6 Fatty Acids and Biomarkers of Inflammation in the Framingham Offspring Study. Nutrients, 17(13), 2076. DOI: 10.3390/nu17132076
"A large-scale study finds that higher blood levels of omega-6 do not increase markers of inflammation.
A recent study published in the journal Nutrients sheds new light on the ongoing debate surrounding omega-6 fatty acids and their potential role in inflammation.
Public concern over seed oils has been growing, largely because many of these oils are rich in linoleic acid (LA), an essential omega-6 fatty acid. Critics argue that Western diets are overloaded with LA, suggesting this shift is a key contributor to many modern health issues.
According to this view, elevated levels of LA are believed to drive chronic inflammation. But is there solid evidence that consuming more LA — and having higher levels of it in the bloodstream — actually leads to increased inflammation?
Investigators relied on data from the Framingham Offspring Study, a well-known research cohort from the Boston area. The Framingham Offspring Study is a landmark longitudinal research initiative that follows the children of participants in the original Framingham Heart Study to investigate genetic and lifestyle factors influencing cardiovascular and metabolic health. Launched in 1971, it has provided decades of valuable insights into chronic disease risk and prevention. The cohort's rigor and continuity make it one of the most trusted sources for understanding long-term health trajectories.
Study Design and Biomarker Analysis
This was a cross-sectional study, meaning that the LA and arachidonic acid (AA) levels were measured in the same blood samples as the 10 inflammation-related biomarkers in 2700 individuals. The relationships between the levels of these two omega-6 fatty acids and 10 separate blood/urine biomarkers of inflammation and oxidative stress were statistically evaluated.
After adjusting (controlling statistically) for multiple other potentially confounding factors (age, race, sex, smoking, blood lipid levels, blood pressure, body weight, etc.), the researchers found that higher LA levels were associated with statistically significantly lower levels of five of the 10 biomarkers, and in no case was higher LA related to higher levels of any biomarker. For AA, higher levels were linked with lower concentrations of four markers, and, like LA, there were no statistically significant associations with higher levels of inflammation/oxidation.
Implications for Dietary Recommendations
"These new data show clearly that people who have the highest levels of LA (and AA) in their blood are in a less inflammatory state than people with lower levels. This finding is exactly the opposite of what one would expect if omega-6 fatty acids were 'proinflammatory' – in fact, they appear to be anti-inflammatory," explained study investigator William S. Harris, PhD; President Fatty Acid Research Institute; Founder, OmegaQuant Analytics, LLC; and Professor, Department of Internal Medicine, Sanford School of Medicine, University of South Dakota, Sioux Falls, SD.
"In the flurry of news stories about the harms of seed oils – the primary sources of LA in the diet – many voices are calling for reducing Americans' intakes of LA. This is not a science-based recommendation, and this study – in addition to many more – point in precisely the opposite direction: instead of lowering LA intakes, raising intakes appears to be a healthier recommendation," Dr. Harris continued. "These findings contradict a narrative, not previous research findings. There are many studies in the medical literature that are consistent with our findings here."
Reference: "Red Blood Cell Omega-6 Fatty Acids and Biomarkers of Inflammation in the Framingham Offspring Study" by Heidi T. M. Lai, Nathan A. Ryder, Nathan L. Tintle, Kristina H. Jackson, Penny M. Kris-Etherton and William S. Harris, 21 June 2025, Nutrients.