Are Seed Oils Bad for You? Olive Oil vs. Seed Oils — The Evidence

Seed oils — soybean, corn, canola, sunflower, safflower — are being called "toxic" and "the root of all disease" all over social media. The claim: they cause inflammation and heart disease, so you should swap them all for olive oil. Is any of that true? Only part of it. The biggest studies point the opposite way — but olive oil still wins.

Evidence Tier: 🥈 Silver — large observational studies and meta-analyses, but the randomized-trial evidence is old and conflicting.

📋 Simple Summary

Seed oils are cooking oils made from seeds, like soybean, corn, canola, sunflower, and safflower. Lots of online videos call them toxic and blame them for heart disease.

But the biggest studies — one of 68,000 people and another of 811,000 people — found the opposite. People with more of these oils in their body tended to live a bit longer, not shorter.

The confusion comes from a few old studies from the 1960s that swapped butter for these oils in already-sick people. Those studies are quoted a lot, but the oils back then also contained a now-banned bad fat called trans fat, which muddies the results.

The honest bottom line: seed oils are not the poison they are made out to be. But olive oil — especially the extra virgin kind — is still the best choice, because it has extra healthy plant compounds that seed oils lack.

The detailed breakdown continues below for those who want the full science.

What Are Seed Oils?

Seed oils are oils pressed from the seeds of plants. The common ones are soybean oil, corn oil, canola oil, sunflower oil, and safflower oil. They are sometimes called "vegetable oils," which is confusing because they actually come from seeds.

These oils are high in a type of fat called omega-6. The main omega-6 fat is called linoleic acid (say "lin-oh-LAY-ick"). This is the molecule most of the "seed oils are bad" argument is about.

Here is the key point: your body needs some omega-6 fat. You cannot make it yourself, so you have to eat it. The question is only how much is okay.

The Claim, and Where It Comes From

The "seed oils are toxic" claim is very popular on social media. It usually makes a few arguments:

• Seed oils are new to the human diet, so our bodies are not used to them.
• Omega-6 fats turn into inflammation in the body.
• Seed oils are made with harsh chemicals and high heat.

There is a small grain of truth in each one. Seed oils are newer than butter and olive oil. Omega-6 fats do play a role in inflammation. And industrial seed oils are heavily processed. But the leap to "seed oils kill you" does not hold up when you look at the big studies.

The Biggest Studies Say the Opposite

Two huge, well-designed studies give us the clearest picture.

The first, published in the journal Circulation in 2019, pooled data from 30 studies across 13 countries, with about 68,000 people. Instead of just asking people what they ate, it measured the actual omega-6 levels in their blood and tissues. People with higher omega-6 levels had a 22% lower risk of dying from heart disease and a 7% lower risk of any heart problem.

The second, a 2020 review in the American Journal of Clinical Nutrition, combined 44 studies with about 811,000 people. People who ate more linoleic acid had a 13% lower risk of dying from any cause, a 13% lower risk of dying from heart disease, and an 11% lower risk of dying from cancer.

That is not what "toxic" looks like. If anything, the biggest and best data suggest omega-6 is neutral or slightly helpful.

The Old Studies Everyone Quotes

So why do so many people say seed oils are dangerous? Because of a few old studies that were re-analyzed years later.

One was the Sydney Diet Heart Study, run in the late 1960s. It gave 458 men who had already had a heart attack either safflower oil (high in omega-6) or their usual diet. When researchers recovered and re-analyzed the old data in 2013, they found the safflower-oil group actually had a higher death rate.

Another was the Minnesota Coronary Experiment, also from the 1960s. It replaced saturated fat with corn oil in about 9,400 people and found no clear benefit — and a slightly higher death rate among those whose cholesterol dropped the most.

These studies are real and worth taking seriously. But they have a big problem: the margarines used back then were often loaded with trans fat, a fat we now know is clearly harmful. It is very hard to tell whether the harm in those old studies came from the omega-6 fat or from the trans fat mixed in with it. That is why they remain hotly debated rather than settled.

What Is Actually Causing the Problem

Here is the important part most online arguments miss. The real dietary problems tied to seed oils are not the oil itself. They are:

• Trans fat. This is the clearly bad fat, now mostly banned. Old margarines and fried foods were full of it.
• Ultra-processed foods. Seed oils are a main ingredient in chips, cookies, and fast food. It may be the junk food around the oil, not the oil, that causes harm.
• Too many calories. Oil of any kind is pure fat and very high in calories. Eating too much of it, from any source, leads to weight gain.

In other words, blaming seed oils alone is like blaming the spoon for the sugar.

Why Olive Oil Still Wins

None of this means seed oils are better than olive oil. Olive oil still comes out on top, and for a clear reason.

Extra virgin olive oil is packed with polyphenols — natural plant compounds that fight inflammation and protect cells. Seed oils lose most of these compounds during heavy processing. Plus, olive oil has the strongest long-term health data of any oil: big studies link it to a 15–19% lower risk of death (we cover that in detail on our olive oil page).

So the honest ranking is simple: olive oil is the best all-around oil. Seed oils are fine, not poison. The thing to actually avoid is trans fat and too much ultra-processed food.

The Honest Verdict

What This Means for You

• Do not fear seed oils. A little canola or avocado oil for cooking is not going to hurt you.
• Use extra virgin olive oil for most things. Drizzling, salads, and low-heat cooking are where it shines.
• For high-heat cooking (frying, searing), a seed oil with a high smoke point is actually a reasonable choice — olive oil can smoke and break down at very high heat.
• Focus on whole foods. The oil you cook a vegetable in matters far less than eating the vegetable instead of a bag of chips.
• Avoid trans fat (check labels for "partially hydrogenated" oil) and cut back on ultra-processed food. That is where the real risk is.

Frequently Asked Questions

Are seed oils bad for you?

No, the evidence does not support the claim that seed oils are toxic. Large studies of hundreds of thousands of people found higher omega-6 levels were linked to lower, not higher, risk of death and heart disease. The real problems are trans fat and too much ultra-processed food.

Do seed oils cause inflammation?

The idea that omega-6 fats simply "turn into" inflammation is oversimplified. In large studies, higher omega-6 in the blood was linked to a lower risk of heart disease, not higher. Your body needs some omega-6 fat.

Is olive oil better than seed oils?

Yes, extra virgin olive oil is the best all-around oil. It has polyphenols — natural plant compounds that fight inflammation — that heavily processed seed oils have lost, and it has the strongest long-term health data of any oil.

What is the best oil for high-heat cooking?

For frying or searing, oils with a high smoke point work best, such as avocado oil or refined canola oil. Extra virgin olive oil can break down and smoke at very high heat, so save it for drizzling, dressings, and low-heat cooking.

What about the old studies that showed seed oils increased deaths?

Those studies — the Sydney Diet Heart Study and the Minnesota Coronary Experiment — were run in the 1960s using margarines that often contained trans fat, a fat we now know is clearly harmful. It is hard to know if the harm came from the omega-6 or the trans fat, which is why the results remain debated rather than settled.

Sources

1. Marklund M, Wu JHY, Imamura F, et al. Biomarkers of Dietary Omega-6 Fatty Acids and Incident Cardiovascular Disease and Mortality. Circulation. 2019. PMID 30971107
2. Li J, Guasch-Ferré M, Li Y, Hu FB. Dietary intake and biomarkers of linoleic acid and mortality: systematic review and meta-analysis of prospective cohort studies. Am J Clin Nutr. 2020. PMID 32020162
3. Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ. 2013. PMID 23386268
4. Ramsden CE, Zamora D, Majchrzak-Hong S, et al. Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ. 2016. PMID 27071971

Disclaimer: We are researchers, not doctors. Nothing on this page is medical advice. Talk to your doctor before making major changes to your diet.