What Are Seed Oils and Are They Bad for You?

The “hateful eight” might be the band of violent travelers from a Quentin Tarantino movie, but they’re also an octet of seed oils — canola, corn, sunflower, safflower, soy, grapeseed, rice bran and cottonseed — that social media influencers have deemed toxic. Experts say scientific evidence doesn’t support these claims, so we’ve unpacked the good and the bad about these oils made from seeds.


What Is a Seed Oil?

Vegetable oils are edible oils extracted from plants or seeds. Seeds oils, such as the so-called “hateful eight,” are the oils that specifically come from plant seeds.

“You take the seed, and when you squish it, oils come out,” explains Jeanne Freeland-Graves, the Bess Heflin Centennial Professor and division head of nutritional sciences at the University of Texas at Austin in Austin, Texas. “We’ve been doing this for centuries.”

This process of extracting oil is known as “cold-pressing,” meaning the oil is derived without heat, Freeland-Graves adds. Cold-pressed oils may be higher in nutrients, but they have a shorter shelf-life, take longer to produce and usually result in smaller quantities.

These cold-pressed oils, Freeland-Graves notes, may also be cloudier. To refine the oil and reduce the cloudiness, manufacturers sometimes use heat, which oxidizes — or breaks down — the oil. They might also use other chemicals or pressure to extract and purify the oil. It’s the heat and the fatty composition of these oils where naysayers come in.

[SEE: 10 Best Mediterranean Diet Snacks.]

What’s in Seed Oils?

Seed oils contain three types of fat in varying amounts: saturated, monounsaturated and polyunsaturated fats. Seed oil critics have zeroed in on polyunsaturated fats, also known as PUFAs, which contain both omega-3 and omega-6 fatty acids. Omega-3 — which is found in foods such as salmon, tuna and walnuts — is critical for heart and brain health.

“Research has suggested that omega-3 fatty acids may help to decrease the risk of blood clots, improve blood lipid levels, decrease blood pressure, protect against irregular heartbeats and suppress inflammation, thereby supporting brain health and decreasing the risk of some cancers,” says Nancy Farrell, a Fredericksburg, Virginia-based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics.

[See: 13 Best Fish: High in Omega-3s — and Environment-Friendly.]

Seed Oils and Inflammation

Omega-6 has a murkier reputation. Previously, it was largely considered unhealthy because of its link to inflammation, says Dr. Marijane Hynes, clinical professor of medicine at the George Washington University School of Medicine and Health Sciences in Washington, D.C.

The most common omega-6 is linoleic acid, which the body converts into arachidonic acid. Arachidonic acid plays a complex role in inflammation and has been linked to both inflammatory and non-inflammatory reactions in the body.

Research, however, suggests that linoleic acid and arachidonic acid may have some beneficial effects.

In a 2017 study, for example, researchers determined that linoleic acid intake did not have a significant effect on the blood concentration of inflammatory markers. Similarly, a 2015 study suggests that linoleic acid does not promote inflammation. Furthermore, a 2021 study in the American Heart Association’s journal Cardiology found that linoleic and arachidonic acid are associated with a lower risk for cardiovascular disease and that linoleic acid could play a role in prevention of the disease. A 2022 study even found that linoleic acid could be associated with better physical function in adults over age 70.

“Linoleic acid is important in supporting healthy blood cholesterol levels,” Farrell explains, adding that in general, omega-6 fatty acids can “help to maintain bone health, improve skin — eczema or psoriasis, for example — and hair health, regulate metabolism and support a healthy reproductive system.”

While these findings are promising, experts say more research needs to be completed. Farrell also notes that you need to balance your omega-3 and omega-6 consumption to maximize health.

“Too much of one of these fatty acids can create a deficiency of the other as they compete for enzymes for formation,” Farrell explains. “The most effective mechanism is for the diet to supply adequate amounts of both omega-3 and omega-6 fatty acids.”

[READ: Mediterranean Eating Habits That Support Healthy Aging.]

Balancing Omega-3 and Omega-6 With Seed Oils

Omega-3 and omega-6 aren’t made by the body, which means they must come from your diet, Farrell explains. To ensure you’re getting enough of both fatty acids, she suggests eating omega-6 and omega-3 at a 2-to-1 or 4-to-1 ratio. Typically, people consume them at a 17-to-1 ratio, due to the high amounts of omega-6 in oils used in fast food and in convenience foods.

Generally, the Academy of Nutrition and Dietetics recommends that women ages 19 to 50 consume 12 grams of omega-6 fatty acids each day, while men ages 19 to 50 should consume 17 grams of omega-6 fatty acids daily. According to the government’s Dietary Guidelines for Americans, the total recommended amount of oil consumed is 27 grams, which is equivalent to approximately 2 tablespoons, per day on a 2,000-calorie diet.

The problem, experts point out, is that we typically eat more than that because seed oils are often found in unhealthy, highly processed foods, such as:

— Baked goods.

— Candy.

— Margarine.

— Crackers.

— Mayonnaise.

— Salad dressings.

— Chips.

They’re also commonly used as frying oils, which is when heat becomes a factor.

The Basics of Heating Oils

Some oils that can handle higher cooking temperatures include safflower, sesame, olive and avocado oil. But a good rule of thumb to follow is to never reuse cooking oil.

When you start heating oil, PUFAs can create harmful chemicals, such as hydroxides and aldehydes, which experts have linked to inflammation.

Reheating these oils, when they continue to break down, can be a health concern because this process produces fumes and compounds that can be carcinogenic, which are substances and compounds that have been shown to cause cancer by affecting both cells and the DNA within cells.

Restaurants, Freeland-Graves and Hynes add, tend to be guilty of reheating oil.

“You should never reheat oils. You’re supposed to use them once and then throw them away,” Freeland-Graves explains. “But (in the) food industry, they can’t afford to do that. Good restaurants will change their oils and discard them, but that’s expensive.”

Using Seed Oils at Home

To avoid consuming reheated seed oils — and potentially unhealthy food — Hynes recommends cooking at home. Not only will you save money, she says, but you’ll also save on calories; when you eat out at a restaurant, you typically eat an extra 400 calories.

If you’re frying at home, you should look out for color changes or smoke and never reheat the oil. Freeland-Graves recommends using canola oil, while Hynes’s preference is extra-virgin olive oil, which is an unrefined, heart-healthy oil.

If you’re baking, Freeland-Graves suggests using butter or, for a healthier alternative, applesauce as a substitute for oil.

The Takeaway

When used appropriately, seed oils are not the bad guys they’ve been made out to be. However, because seed oils often appear in unhealthy foods, such as french fries and onion rings, as well as cookies and candy, you’re better off getting fatty acids — including omega-3 and omega-6 — from whole foods, such as fish (salmon, mackerel and herring), sunflower seeds, tofu, peanut butter, eggs, chia seeds, walnuts and almonds.

More from U.S. News

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What Are Seed Oils and Are They Bad for You? originally appeared on usnews.com

Update 03/13/23: This story was previously published at an earlier date and has been updated with new information.

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