The “hateful eight” might be the band of violent travelers from a Quentin Tarantino movie, but they’re also an octet of seed oils that social media influencers have deemed toxic:
— Canola oil.
— Corn oil.
— Sunflower oil.
— Safflower oil.
— Soy oil.
— Grapeseed oil.
— Rice bran oil.
— Cottonseed oil.
Experts say scientific evidence doesn’t support these claims, so we’ve unpacked the good and the bad about these vegetable oils made from the seeds of a plant. We’ll also take a look at other vegetable oils.
What Are Seed Oils and Vegetable Oils?
Vegetable oils — such as olive oil and coconut oil — 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. “We’ve been doing this for centuries.”
This process of extracting oil is known as “cold-pressing,” meaning the oil is derived without heat. 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 heating process and the fatty composition of these oils that bring in the naysayers.
[SEE: 10 Best Mediterranean Diet Snacks.]
Are Seed Oils and Vegetable Oils Bad for You?
Vegetable oils and seed oils contain three types of fat in varying amounts, some of which are essential in a healthy, balanced diet: 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.
Omega-6 has a murkier reputation. The most common omega-6 is linoleic acid. The body converts linoleic acid into arachidonic acid, a polyunsaturated fatty acid that plays a complex role in inflammation and has been linked to both inflammatory and non-inflammatory reactions in the body.
Previously, omega-6 fatty acids were largely considered unhealthy because of their 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. But much of those conclusions were based on small or animal and lab-based studies with little statistical significance or reliability.
[See: 13 Best Fish: High in Omega-3s — and Environment-Friendly.]
Potential Benefits of Seed Oils
Research, however, suggests that the linoleic acid and arachidonic acid in seed oils may actually have some beneficial effects.
Studies, including one from 2017 and another from 2015, suggest that linoleic acid does not have a significant effect on blood markers of inflammation or inflammation as a whole. Furthermore, a 2021 study in the American Heart Association’s journal Cardiology found that linoleic and arachidonic acid were 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.”
Balancing omega-3 and omega-6 fatty acids
Omega-3 and omega-6 fatty acids aren’t made by the body, which means they must come from your diet, Farrell says. 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, however, 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 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 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.
[READ: Mediterranean Eating Habits That Support Healthy Aging.]
Smoke Points and Cooking Methods of Different 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. Carcinogens are substances and compounds that have been shown to cause cancer by affecting both cells and the DNA within cells.
Restaurants 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.”
Cooking and Storing 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 consume 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 substituting oil for butter or, for a healthier alternative, applesauce.
Try to buy oils in darker containers, and make sure to keep them stored in a dark space to prevent light from deteriorating the quality of the oil.
Environmental Impact of Oils
While oils tend to be an integral part of our daily diet, they can have a negative impact on the environment. Palm oil, a common vegetable oil found in both food and consumer products, has been linked to deforestation and climate change, specifically increased greenhouse gas emissions and air pollution, according to a 2020 review.
Olive oil also produces environmental waste, as shown in a 2023 review in Environmental Science and Pollution Research. Conversely, data from the International Monetary Fund indicated that climate change is affecting olive oil supply; high temperatures and drought in Spain have reduced olive growth, and prices have subsequently spiked.
The solution, say the authors of a 2023 study in Frontiers in Public Health, lies in collaboration: “Experts in nutrition, health, agronomy, food production, economy, sociology and governments need to work together with the common goal of feeding the world sustainably in the next future.”
In the meantime, what does that mean for the individual consumer? You can opt out of some oil-based cooking methods, such as frying, and try air-frying instead. Hynes also suggests swapping out some oils for nuts and avocados, which have additional healthy components, such as antioxidants, minerals and fiber.
Considering Oils Within a Balanced Diet
When used appropriately, vegetable oils are not the bad guys they’ve been made out to be. However, because some 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 from whole foods, such as fish (salmon, mackerel and herring), sunflower seeds, tofu, peanut butter, eggs, chia seeds, walnuts and almonds.
Keep serving sizes small, swap out oils when you can and make sure you’re eating a colorful collection of nutrient-dense foods. You might start with tips inspired by the Mediterranean diet: Eating lean proteins mixed with fresh produce and whole grains (and a smattering of extra-virgin olive oil) can be the foundation of a healthy, long-lasting eating pattern.
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Are Seed Oils and Vegetable Oils Bad for You? originally appeared on usnews.com
Update 10/11/23: This story was previously published at an earlier date and has been updated with new information.
