Menu

Are Seed Oils Bad For You? (November 2025)

Carrie Dennett, MPH, RDN

Social media, podcasts and the internet can be a mixed bag of nutrition and health information, and one questionable bit that’s been making the rounds for a while is that seed oils—cooking and salad oils pressed from canola, corn, cottonseed, grapeseed, rice bran, sunflower, safflower and soy—make you sick, causing everything from heart disease and diabetes to leaky gut and brain fog.. 

Are seed oil inherently unhealthy, or are they a victim of guilt by association and misunderstanding of the research? It looks like the latter.

Let’s start with guilt by association. Yes, some people say they felt better after they cut out seed oils. But how did they cut them out? Many seed oils are used in commercially fried foods and ultra-processed foods, such as the type of packaged snack foods that have a very long shelf life. These foods are typically also high in added sugar and sodium and refined flour, while lacking fiber and nutrients—so if someone stops eating them and feel better, it’s likely because of the foods themselves, not just the oils they contain.

Now let’s get into the science. Recommendations to replace most of the saturated fats—fat from animals, plus coconut oil—in our diet with heart-healthy unsaturated fats goes back decades. Unsaturated fats include:

  • Monounsaturated fats, found in olive, avocado, canola, peanut, safflower and sesame oil as well as avocados, peanut butter and many nuts and seeds.
  • Polyunsaturated fats, found in soybean, corn and sunflower oil, as well as walnuts, salmon, flax seed, sunflower seeds, tofu and soybeans.

All fats and oils are a mix of saturated, monounsaturated, and polyunsaturated fatty acids. For example, canola oil is about 7% saturated fat, 63% monounsaturated fat, and 30% polyunsaturated fat. Other seed oils tend to be higher in polyunsaturated fats. It’s well established that omega-3 polyunsaturated fats—found in fatty fish, walnuts, flax seeds and canola—are good for us. What’s more controversial are omega-6 polyunsaturated fats. 

One criticism of seed oils is that they’re too high in omega-6 fatty acids—especially linoleic acid—and this can cause inflammation in the body. The reasoning is that linoleic acid turns into a different fatty acid, arachidonic acid, in the body, and arachidonic acid is a building block for compounds that cause inflammation. 

However, only a small percentage of linoleic acid is converted to arachidonic acid—which is also a building block for compounds that fight inflammation. The inflammatory claims are mostly based on research in rodents, and mice and rats don’t respond to linoleic acid the same way humans do. In fact, human research has found it’s not inflammatory overall.

A 2017 review and analysis of 30 randomized controlled trials involving 1,377 people found no connection between a diet high in linoleic acid and markers of inflammation. A 2019 review of 30 observational studies from 13 countries involving 68,659 people found that high levels of linoleic acid were associated with lower risk of cardiovascular events, such as heart attacks.

Another criticism is that seed oil manufacturers use heat and solvents, such as hexane, to extract oil from seeds, creating unhealthy trans fats and chemical contaminants. However, seed oils contain little residual hexane, a mere fraction of what you inhale from car exhaust when walking along streets or roads. And heating during processing is brief, so any trans fats created are very minimal. When it comes to heat, the real problem is when seed oils are reheated, as they are in commercial deep fryers. This oxidizes the oils, and oxidized oils are inflammatory.

So what does this mean for you? First, don’t worry about seed oils. Second:

  • Eat a variety of foods and a variety of fats. There are many sources of healthful fats. Nuts and nut oils. Whole seeds such as sunflower, pumpkin, chia and flax. Avocados and avocado oil. Fatty fish. Olives and olive oil. 
  • Treat your oils with care. The four enemies of any cooking or salad oil are heat, light, oxygen and time. Store all oils in a cool, dark cabinet (especially if they are in clear bottles), or in the refrigerator if recommended on the label. Screw caps back on tightly once opened. If you don’t use a lot of a certain oil, don’t buy a big bottle of it. 

References:

Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 fatty acids and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009 Feb 17;119(6):902-7. https://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.108.191627

Su H, Liu R, Chang M, Huang J, Wang X. Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials. Food Funct. 2017 Sep 20;8(9):3091-3103. https://pubmed.ncbi.nlm.nih.gov/28752873/

Marklund M, Wu JHY, Imamura F, et al; Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Fatty Acids and Outcomes Research Consortium (FORCE). Biomarkers of Dietary Omega-6 Fatty Acids and Incident Cardiovascular Disease and Mortality. Circulation. 2019 May 21;139(21):2422-2436. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.118.038908

Related Posts