Seed Oils Are Under Attack, but Are They Actually Bad for You?
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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.
But there’s a big issue with this theory: These results haven’t panned out in any studies looking for inflammatory markers or disease outcomes in real people eating a good deal of omega-6s, Dr. Mozaffarian says. In fact, research has consistently shown that high consumption of linoleic acid—the most prevalent omega-6 in food sources—has either no effect on inflammation in the body or is associated with lower levels, he says. It turns out, only a tiny portion (about 0.2%) of the linoleic acid we eat gets converted into that arachidonic acid, and the rest may become anti-inflammatory (!) compounds. But that message has gotten twisted. “People realized that omega-3s are a little better than omega-6s at being anti-inflammatory, and that got flipped to: ‘Omega-6s are pro-inflammatory,’” Dr. Gardner says. “But just because they’re not as good doesn’t mean they’re bad.”
Indeed, other studies have found that high omega-6 intake is linked to a reduced risk of type 2 diabetes and cardiovascular disease, as well as death from any cause. Some of these benefits also stem from linoleic acid’s separate ability to lower levels of “bad” LDL cholesterol, Frank M. Sacks, MD, a professor of cardiovascular disease prevention at the Harvard School of Public Health and lead author on the AHA advisory above, tells SELF. He also points to a large body of research showing that when people replace animal fats like butter or tallow in their diet with plant oils (including seed oils), their heart-health metrics get better—not worse.
Still, you might question whether we’re going overkill on omega-6 at least relative to omega-3, in light of the fact that today’s Western diet includes about 16 times as much of the former as the latter (whereas our ancestors ate them equally). There’s ample debate over the “ideal” ratio and whether it’s worth it or even possible to aim for one-to-one, given both the upsides of omega-6s we now know and their greater prevalence in our food supply. What experts agree on, however, is that we’re taking in “abysmally low” amounts of omega-3, Dr. Mozaffarian says. So it’s more practical and worthwhile to shift your ratio by eating more omega-3 (via fish, walnuts, flaxseed, and, yes, seed oils that have some of these fats, like canola and soybean) versus consuming less omega-6.
2. The claim: The industrial process used to make seed oils includes toxic chemicals or makes the end product harmful.
As noted above, manufacturers typically lean on chemicals called solvents, specifically hexane (which is toxic if you repeatedly inhale the gas form), to draw out the max amount of oil from seeds. And that has stoked concerns about chemical bits lingering in the final product. But the good news is, the use of heat in later stages of processing evaporates the hexane, so the final oil contains only a tiny amount, if any—too low to have a negative effect, according to the Agency for Toxic Substances and Disease Registry.
Once the oil has been extracted, it also undergoes some refining. The point is to strip away contaminants (like pesticides or trace metals) as well as other compounds that make the oil prone to going rancid, give it a harsh taste or smell, or darken its color. These practices can admittedly destroy some of the oil’s naturally beneficial components, too, including antioxidants like polyphenols, and introduce very low levels of some unsupportive compounds, such as trans-fatty acids, Dr. Mozaffarian says. But to be clear, this doesn’t cancel out the benefits of the ample healthy fats they include, nor does it transform them into something toxic. As Dr. Mozaffarian explains, the fact that seed oils might be slightly better for us if we could make them with less refining is still distinct from them being harmful.
Relatedly, some seed oil detractors are more worried about toxic byproducts developing when they fry or sauté with them. While it’s true that the unsaturated fat in seed oils is more susceptible to oxidation (a.k.a. degradation) with heat exposure than the saturated fat in, say, butter or lard, the refining process boosts the oil’s stability and smoke point to prevent that, Dr. Gardner says. (This is also why cold-pressed oils burn more easily and are best used chilled, like in salad dressing.) And though some research suggests that seed oil breakdown at high temperatures may trigger the production of harmful compounds, these results have only been shown in oils that have been repeatedly reheated and reused, like in a restaurant’s deep fryer—a very different situation from heating any one serving of oil (fresh from the bottle) a single time to cook a meal at home.
3. The claim: Because we’re consuming more seed oils and experiencing more chronic disease, the former is causing the latter.
The final layer of the anti-seed-oil argument draws a parallel between the sharp rise in seed oil intake over the past century and the hike in rates of chronic disease. But that leaves out a very important factor: how we’re consuming these oils. “What I would love to hear is that people have been making twice as many salads and using these oils in their dressings, or they’ve been sautéing the hell out of their vegetables,” Dr. Gardner says. But that’s certainly not the case. Usage has gone up, he says, because of ultraprocessed foods.
Mass-produced via industrial techniques, these items (including things like packaged cookies and chips) are often laden with seed oils and make up nearly 60% of the average American diet. The catch is, almost every one of them also has added sugar, added salt, and refined grain—all of which research suggests may contribute to the inflammation at the root of many chronic conditions, Dr. Gardner says. So we can’t accurately conclude that seed oils are causing more disease when so many other factors are in play.
The takeaway: Seed oils are healthy to use for cooking and preparing meals—but they’re also included in some not-so-beneficial ultraprocessed foods.
Nothing about the contents of seed oils or how they’re produced makes them deleterious or harmful. Quite the contrary, they’re rich in omega-6 fatty acids, which research shows are heart-healthy. Might it be extra-important to focus on eating omega-3s, given how little of them we tend to consume in comparison? Sure. But both play a role in a balanced diet.
While seed oils do tend to be present in many ultraprocessed foods, that doesn’t mean they’re to blame for any associated health risks: Again, research places the guilt squarely on the other less-supportive ingredients found in these items. When it comes to cooking, seed oils are a net good, and you should feel fully empowered to drizzle, sauté, and stir-fry as you please. The bottom line, says Dr. Mozaffarian: “Don’t be afraid of fat, and don’t be afraid of seed oils.”
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Originally Appeared on Self
