In wellness-minded corners of the internet, seed oils (a.k.a. oils made from the seeds of plants) have been pariahs for several years, with folks of varying credentials calling them out as “toxic,” branding a set of them as “the hateful eight,” and even suggesting they’re the root cause of a swath of chronic diseases. But as of late, they’ve soared to mainstream infamy, as influencers on TikTok have taken to disparaging these oils and, notably, Robert F. Kennedy Jr. (president-elect Donald Trump’s pick to head the Department of Health and Human Services) has claimed that we’re being “unknowingly poisoned” by them. But should we really view seed oils as Public Enemy No. 1?
It turns out, the science isn’t nearly so definitive—and much of it actually points in the opposite direction, suggesting that seed oils may support your health, depending on how (and in what quantity) you eat them. Indeed, the American Heart Association (AHA) even released a presidential advisory in 2017 recommending that folks eat less saturated fat (found in things like butter, lard, and coconut and palm oils) in favor of consuming more unsaturated fat, like the kind in seed oils, to lower their risk of developing cardiovascular disease. It’s the reason why Christopher Gardner, MD, a professor of medicine and nutrition scientist at Stanford University, tells SELF he’s befuddled by the malignment of seed oils in the popular discourse: “The way [people are] talking about them is so bizarrely demonized.”
Concerns swirling around seed oils seem to have emerged from a confluence of unrelated concepts, including the negative connotation of processed foods and a misunderstanding of how certain fats affect the body, Dariush Mozaffarian, MD, a cardiologist, public health scientist, and director of the Food is Medicine Institute at Tufts University, tells SELF. Below, he and other nutrition researchers break down how this common cooking ingredient became an easy—if misguided—scapegoat for major health woes, and why the effects of seed oils are actually more good than bad for you. (Yes, really.)
What oils are seed oils?
Technically, a seed oil is just any oil extracted from a plant’s seed. But the ones at the center of this controversy are the eight that are most commonly used in cooking and industrial food production: canola, corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils. What also unites them is the main type of fat they include: a polyunsaturated fat called an omega-6 fatty acid.
The way such seed oils are typically made also contributes to their vilification. Whereas something like an olive or avocado, for instance, can be readily squeezed to draw out the oil (called “cold-pressed” or “virgin”), you can imagine that doing the same to a bunch of little seeds would be way less efficient, Dr. Mozaffarian explains. So most seed oils you’ll find in the grocery store are extracted by way of chemicals and heat, he says. (Chemical-free cold-pressed options exist for certain seeds but are rarer and pricier.) They’re also typically refined further to strip them of any funky flavors and increase their shelf life and stability (more on this below).
The main arguments against seed oils—and what the science actually says
1. The claim: The type of fat in seed oils causes inflammation.
At the heart of the case against seed oils are concerns about the omega-6 fatty acids that are abundant in them. Like its better-known cousin omega-3, omega-6 is essential for healthy brain and cell functioning, and we have to get both via food, since the body can’t make them. What’s less clear is how much of each fatty acid is optimal, and exactly how they interact with each other once we eat them. Some research in human cells (conducted in a lab, not in the body) and animals has suggested that they may compete or have opposing effects, at least at the cellular level: While your body turns omega-3 into compounds called resolvins that tamp down inflammation, it converts omega-6 into chemicals like arachidonic acid that can do the opposite. Hence the fear that too many omega-6-laden seed oils—and too little omega-3s—might up your risk for developing a chronic inflammation-fueled condition like heart disease or cancer.
