Seed Oils and Cardiovascular Health: A Review of the Evidence

The category of vegetable oils commonly described in consumer discussion as “seed oils” — including soybean, canola, sunflower, corn, safflower, and cottonseed oils — has been the subject of renewed public debate on U.S. social-media platforms. The oils in question are high in polyunsaturated fatty acids, particularly linoleic acid, an essential omega-6 fatty acid.

This Bulletin reviews the published evidence on seed-oil consumption and cardiovascular outcomes, summarizes the 2017 Presidential Advisory issued by the American Heart Association, and contrasts the current state of the literature with claims that have circulated in consumer media.

Let's start with what seed oils actually are. The term typically refers to oils extracted from the seeds of plants: soybean oil, canola oil, sunflower oil, corn oil, safflower oil, and cottonseed oil. These oils are high in polyunsaturated fatty acids (PUFAs), particularly linoleic acid, an omega-6 fatty acid. They became dietary staples in the 20th century largely because they were cheaper to produce than animal fats and were promoted as heart-healthy alternatives to saturated fat.

The anti-seed-oil argument usually goes something like this: seed oils are "unnatural," they're highly processed, they contain too much omega-6 which causes inflammation, and their rise in the food supply correlates with rising rates of chronic disease. Some of these points contain grains of truth, but the conclusions drawn from them often leap far beyond what the evidence supports.

The Omega-6 Inflammation Claim

The most common argument against seed oils centers on omega-6 fatty acids. The reasoning goes: omega-6 fatty acids are precursors to pro-inflammatory molecules (eicosanoids), therefore consuming a lot of omega-6 must cause chronic inflammation, therefore seed oils cause heart disease, diabetes, and every other modern ailment.

The problem is that this is a massive oversimplification. While omega-6 fatty acids can be converted to pro-inflammatory compounds, they're also converted to anti-inflammatory ones. A 2019 review published in the journal Circulation found that higher linoleic acid intake was associated with modestly lower risk of cardiovascular events and cardiovascular mortality. The American Heart Association has consistently stated that replacing saturated fats with polyunsaturated fats (including omega-6) reduces cardiovascular risk.

A 2017 meta-analysis in the British Journal of Sports Medicine found no significant association between linoleic acid intake and inflammatory markers in controlled feeding trials. In other words, when researchers actually tested whether eating more omega-6 increased measurable inflammation in humans, it generally didn't.

The "Processing" Argument

Another frequent criticism is that seed oils are "heavily processed" and therefore inherently unhealthy. It's true that most commercial seed oils undergo processes including degumming, bleaching, and deodorizing. These sound scary, but the question that matters is whether the final product is harmful, not whether the process sounds unpleasant.

Olive oil, often held up as the gold standard of healthy fats, also undergoes processing. "Extra virgin" means minimally processed, but refined olive oil goes through similar steps to refined seed oils. The processing argument, taken to its logical conclusion, would also condemn most of the foods we eat, including cheese, bread, chocolate, and wine.

What the Actual Evidence Shows

The largest and most rigorous studies generally find that replacing saturated fat with polyunsaturated fat (the main fat in seed oils) is associated with lower cardiovascular risk. This doesn't mean seed oils are a superfood. It means the claim that they're uniquely toxic is not supported by the bulk of the evidence.

That said, there are legitimate nuances worth considering. Seed oils are calorie-dense, and their prevalence in ultra-processed foods means that people who eat a lot of processed food will consume a lot of seed oils by default. But the problem there is likely the ultra-processed food pattern itself, not the specific oil used.

The Bottom Line

Are seed oils the dietary villain that social media makes them out to be? The evidence says no. Are they a magical health food? Also no. They're a relatively neutral source of calories and essential fatty acids that can be part of a healthy diet.

The seed oil panic is a textbook example of how wellness culture takes a kernel of biological truth (omega-6 fatty acids can be converted to inflammatory compounds), strips away all the context and complexity, and turns it into a simple, shareable narrative that sounds scientific but isn't.

If you want to improve your diet, the evidence consistently points to the same boring advice: eat more vegetables, fruits, whole grains, and legumes. Exercise regularly. Sleep enough. Manage stress. Whether your salad dressing contains canola oil or olive oil is very far down the list of things that will meaningfully impact your health.

But that advice doesn't sell supplements. And it definitely doesn't go viral.

Embrace the soy.