Seed Oils: What the Science Actually Shows

Seed oils are currently one of the most debated topics in nutrition. Social media claims often suggest they are toxic, pro-inflammatory, or even responsible for chronic disease. But when we look at the actual body of research, the picture is far more nuanced.

As a food scientist, my goal here is not to defend or demonize seed oils — but to explain what the science supports, what it doesn’t, and where common claims go too far.

What Are “Industrial Seed Oils”?

Industrial seed oils are oils extracted from seeds using mechanical pressing and/or solvent extraction. The most commonly used include: soybean oil, canola oil, corn oil, sunflower, and safflower oil. They are widely used in the food industry due to their neutral flavor, stability, and low cost.

Typical Processing Steps

_Bloghttps://www.cookingoilmillmachinery.com/FAQ/cooking_oil_pressing_method_vs_cooking_oil_solvent_extraction_method_235.html

One of the most common concerns raised about seed oils is the use of hexane during processing. Hexane is widely used because it is highly effective, stable, and easily evaporated. After extraction, the oil is heated and refined, causing hexane to evaporate completely due to its low boiling point. Understandably, when we hear that a petroleum-based substance is used to process these oils, it raises alarms. Seed oils may contain trace amounts of hexane but often undetectable or below 1 part per million and highly regulated. There are no studies that link hexane, used as a solvent in food oils, to any harmful health effects. That being said, there are no studies that necessarily show that hexane is not the culprit either – it just hasn’t been done yet. It also warrants, if we look at the seed oil industry holistically, we should be concerned with the occupational exposure for those in the factory that are exposed to higher concentrations and at greater risk.

Omega-6 vs Omega-3: Why the Ratio Matters

All of these oils are high in polyunsaturated fats, otherwise known as Omega-6 fatty acids and is where a lot of the controversy stems from. Omega 6- fats are essential fatty acids, meaning our body cannot make them, and play an important role in our immune signaling and cell membrane structure. Another type of essential fats are Omega-3s that are commonly found in fatty fish, flax, and chia seeds.

Historically, the human diet had an omega-6 to omega-3 ratio closer to 2:1 to 4:1. Today, the modern Western diet provides far more omega-6 than omega-3 fats and this ratio often exceed 15:1 or even 20:1, largely due to increased seed oil consumption through ultra-processed foods. This imbalance – not the omega-6 fats themselves – is a concern.

Do Seed Oils Cause Inflammation?

Omega-6 fats do not consistently raise CRP, IL-6, or TNF-α, common markers of inflammation. In fact, when we look at studies, human trials generally show neutral or beneficial effects of seed oils on cholesterol and cardiovascular risk. The LA Veterans Administration Hospital Study (1969) showed that by replacing saturated fats with vegetable oils there was a significant reduction in serum cholesterol and no increase in total mortality (Dayton et al., Circulation). The data shows that Omega-6 fatty acids aka seed oils themselves do not appear to be the problem.

The Real Problem: Overconsumption & Ultra-Processed Foods

The strongest evidence I see against seed oils is not that they themselves are the problem but that their rise in use also mirrors that of the explosion of ultra-processed foods. Since the 1900s, soybean oil consumption has increased a 1,000 fold. Seed oils are a major fat source in processed foods contributing 9 calories per gram. 1 tablespoon is equivalent to 13-14grams aka 1 tablespoon of seed oils contribute roughly 120calories and right now, processed foods make up 60% of calories in the American diet. The data does not show that seed oils themselves are toxic, but because they are calorie-dense, they make it easy for excess calorie intake and we are consuming a lot more of them.

Rather than fearing seed oils, a science-aligned approach would be to limit ultra-processed foods where seed oils are overused, increase omega-3 intake, use a variety of fats including olive oil, butter, and avocado oil, and focus on eating whole nutritious foods.

Alternative Options

I completely understand if there is still hesitation when it comes to consuming these seed oils and quite frankly, if it lists these items on the label, its probably ultra-processed and overall not good for your health. I suggest swapping to whole foods as often as possible but if you’re scanning your nutrition label, look for olive oil, avocado oil, butter, ghee, or coconut oil.

References:

1. Farvid MS, Ding M, Pan A, et al. (2014). Dietary Linoleic Acid and Risk of Coronary Heart Disease: A Systematic Review and Meta-Analysis of Prospective Cohort Studies. Circulation, 130(18), 1568–1578.
   Link
   Shows higher linoleic acid intake is associated with lower risk of coronary heart disease.
2. Hooper L, Martin N, Jimoh OF, et al. (2020). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev, 5, CD011737.
   Link
   A meta-analysis showing that replacing saturated fats with polyunsaturated fats reduces cardiovascular events.
3. Dayton S, Pearce ML, Hashimoto S, et al. (1969). Cholesterol-lowering effect of replacing dietary saturated fat with linoleate-rich corn oil. Circulation, 39, 1–9.
   Early randomized trial demonstrating that linoleic acid from corn oil lowers cholesterol and reduces atherosclerosis.
4. Turpeinen O, Mikkilä V, et al. (1972). Effect of polyunsaturated fats on serum cholesterol and coronary heart disease incidence in mental hospital patients. Am J Clin Nutr, 25(6), 637–646.
   Shows lower coronary disease incidence in patients consuming higher polyunsaturated fat diets.
5. Johnson GH, Fritsche K. (2012). Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review. J Nutr, 142(12), 2175–2180.
   Link
   Summarizes evidence showing linoleic acid does not increase inflammation in humans.
6. Innes JK, Calder PC. (2018). Omega-6 fatty acids and inflammation. Br J Nutr, 111(3), 395–402.
   Link
   Discusses the role of omega-6 fatty acids in inflammatory pathways and cardiovascular health.
7. Ramsden CE, Zamora D, et al. (2013). Use of dietary linoleic acid for secondary prevention of coronary heart disease and death. BMJ, 346, e8707.
   Link
   Reanalysis of an old trial highlighting that omega-6 benefits depend on diet context and omega-3 balance.
8. Monteiro CA, Moubarac JC, Cannon G, et al. (2019). Ultra-processed foods, diet quality, and health using the NOVA classification system. BMJ, 365, l1456.
   Link
   Explains how seed oils are prevalent in ultra-processed foods linked to poor health outcomes.
9. Micha R, Peñalvo JL, Cudhea F, et al. (2017). Association Between Dietary Factors and Mortality From Heart Disease, Stroke, and Type 2 Diabetes in the United States. JAMA, 317(9), 912–924.
   Link
   Large study linking high ultra-processed food intake (including seed oil consumption) to cardiovascular and metabolic risk.