Get your score

Are seed oils toxic?

What you hear: “Canola, sunflower and soybean oils are toxic, cause inflammation and heart disease, and you should cook with butter or tallow instead.”

What the studies found

A review of 15 randomised trials in healthy people found that adding linoleic acid, the main fat in these oils, did not raise any measured inflammation marker. A Cochrane review of 15 trials (about 56,700 people) found cutting saturated fat, often by replacing it with these oils, lowered combined heart events by 17% over at least two years, though deaths did not change. In 221,054 US adults, the biggest butter eaters had a 15% higher death rate than the smallest, while more plant oil went with lower death rates (an observed link). One recovered 1970s trial did not find fewer deaths with corn oil, so the heart benefit is debated, but not the 'toxic' claim.

What you could do

Using liquid plant oils in place of butter or lard is a reasonable, well-supported swap.

See it in the habit library, with what it means for your own longevity score.

Not medical advice. General information from published studies, not a diagnosis or a treatment plan. Talk with your doctor before starting a supplement or changing a medicine, especially if you are pregnant, take other medicines or have a health condition.

How we judged it

Doesn't hold up: Good studies looked and found no benefit, or the claim is plainly false. We judge the claim as it is usually said online, not the habit itself. Trials assign people at random, so they can show cause; observed studies follow people and show a link, not proof. Last checked: October 2026.

The studies, in their own words

1. Johnson & Fritsche, J Acad Nutr Diet 2012

   We conclude that virtually no evidence is available from randomized, controlled intervention studies among healthy, noninfant human beings to show that addition of LA to the diet increases the concentration of inflammatory markers.

2. Hooper et al. Cochrane Database Syst Rev 2020

   The included long-term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular events by 17% (risk ratio (RR) 0.83; 95% confidence interval (CI) 0.70 to 0.98

3. Zhang et al. JAMA Intern Med 2025

   the highest butter intake was associated with a 15% higher risk of total mortality compared to the lowest intake (hazard ratio [HR], 1.15; 95% CI, 1.08-1.22

4. Zhang et al. JAMA Intern Med 2025

   Substituting butter with plant-based oils may confer substantial benefits for preventing premature deaths.

5. Marklund et al. Circulation 2019

   Higher levels of LA were significantly associated with lower risks of total CVD, cardiovascular mortality, and ischemic stroke

6. Ramsden et al. BMJ 2016

   replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes.

More claims, checked

• Doesn't hold upRaw milk
• Doesn't hold upAlkaline water and alkaline diet
• Doesn't hold upA glass of red wine for your heart
• Backed by trialsA 10-minute walk after meals
• Partly trueIntermittent fasting and time-restricted eating
• Partly trueApple cider vinegar before meals

See all 50 claims