More Studies Needed to Quell a Hot Topic
Kitchens around the world use cooking oil for sautéing, baking, and drizzling. Home cooks often keep several types of oils on hand, due to flavor, smoke point, and cost.
But some cooks may not realize there is a boiling debate about some of these oils. Chefs, health coaches, and scientists are arguing about the possibility that seed oils—such as safflower, cottonseed, grapeseed, sunflower, and canola or rapeseed—might be unhealthy.
Studies are still underway, so clearer answers to the heated debate are likely to appear in the foreseeable future. In the meantime, here are some details to make the topic easier to swallow.
The Skinny on Fats
First, it is important to understand fat.
Human bodies require fat from food to survive. Fat provides energy, assists with absorption of vitamins and minerals, plays a role in building cell membranes and the sheaths around nerves, and is necessary for muscle function and blood clotting.
But some fats might also cause harm.
Trans fats are created when oils are processed to prevent spoilage.
Trans fats are created when oils are processed to prevent spoilage. The resulting products include some margarines, shortening, commercial baking oils, and fast-food frying oil.
Because trans fats were correlated with heart disease, stroke, and diabetes, the World Health Organization in 2018 called for their global elimination. As of 2023, 43 countries have agreed to minimize the use of trans fats.
Saturated fats come from animals (butter, lard, processed meats, and fatty meats) as well as some plants (coconut and palm). They are typically solid at room temperature. Saturated fats have been linked to increased cholesterol and arterial blockage. There is evidence that replacing saturated fats with unsaturated fats reduces the risk of heart disease.
Unsaturated fats are thought to be best for health. They fall into two categories: monounsaturated and polyunsaturated.
Monounsaturated fats were discovered to be healthful after the “Seven Countries Study” in the 1960s showed that people in the Mediterranean had low incidence of heart disease despite high-fat diets. The conclusion was that meals built around monounsaturated fats and low saturated fats help protect a person’s heart by maintaining levels of good (HDL) cholesterol while reducing levels of bad (LDL) cholesterol. Some of the plant oils with this profile come from olives, peanuts, rapeseed (canola), and safflower seeds.
the “Seven Countries Study” in the 1960s showed that people in the Mediterranean had low incidence of heart disease despite high-fat diets.
Polyunsaturated fats can provide omega-3 and omega-6 fatty acids, which human bodies cannot produce but need. Oils that provide ample omega-3 include canola, flaxseed, soy (commonly called vegetable oil), and walnut.
Omega-3 fatty acids may lower triglycerides and risk of cardiovascular disease. Omega-6 fatty acids are highest in corn, cottonseed, peanut, soybean, and sunflower oils. Omega-6 may lower bad cholesterol, increase good cholesterol, lower triglycerides, and help control blood sugar.
All oils are 100% fat, but each has a different fat profile.
The Sizzling Debate Over Seed Oils
Critics today argue seed oils are implicated in unwanted weight gain, heart problems, infertility, cancer, and acne—and that they contain toxins that could increase the tendency for Alzheimer’s.
Oil seeds are often harvested from genetically modified crops. The lands on which the farms are growing the crops have sometimes been deforested. Most of the farms use pesticides.
The list of additional complaints associated with seed oils is long. Oil seeds are often harvested from genetically modified crops. The lands on which the farms are growing the crops have sometimes been deforested. Most of the farms use pesticides, which are harmful to beneficial insects and birds. Even when organic, monoculture crops stunt biodiversity.
Another argument against seed oils is that elevated levels of omega-6 fatty acids can cause chronic inflammation when not balanced by omega-3s. According to Cleveland Clinic registered dietitian Julia Zumpano, “If a certain food is high in oils that contain a lot of omega-6s, you really want to try to avoid them or eat them only in moderation.”
Opponents are wary that seed oils are derived through a chemical oil extraction method to yield more oil (and more profit). The oils are heavily refined, heated, bleached, deodorized, and degummed to be usable. The concern is that extensive processing may cause the oils to be susceptible to oxidation and breakdown, which might result in disease-causing free radicals building up in the body.
In addition, various chemical solvents are used for extraction of the oil and residues of these may remain. The high temperature refining process also destroys any beneficial vitamins, phenols, and antioxidants.
“When you bring unsaturated fats repeatedly to high temperatures, you’ll get a buildup of damaging chemicals,”
Guy Crosby, Ph.D., an adjunct associate professor of nutrition at the Harvard T.H. Chan School of Public Health, has expressed concern about seed oils being heated many times. “When you bring unsaturated fats repeatedly to high temperatures, you’ll get a buildup of damaging chemicals,” he says, adding that this is likely only to be a problem in restaurants and factories that use deep fryers. “Cooking with seed oils at home isn’t an issue,” he says.
Proponents of seed oils counter that, in small amounts, seed oils are part of a healthy diet and a necessary source of omega-3 and omega-6 fatty acids. Seed oils also offer a range of flavor profiles and culinary uses.
Seed oil fans note that the studies linking seed oils to adverse health conditions, like heart disease, were conducted on small animals. To date, there are no clinical trials to substantiate that these claims hold true for humans. A 2021 study published in the MDPI journal Nutrients, even associated moderate intake of omega-6 linoleic acid to lower risk of cardiovascular disease.
Seed oil supporters also point out that the oil cannot be blamed when it is part of another product.
Seed oil supporters also point out that the oil cannot be blamed when it is part of another product.
“When you cut seed oils from your diet, what you’re really doing is cutting out many processed foods,” Zumpano says. “I think that’s why we’re hearing about them as being so bad for your health. But it’s less about the seed oils themselves and more about the fact that they’re so often found in ultra-processed foods.”
In addition, there’s even concern about “heating oils to high temperature.”
For instance, flax, hemp, and chia oils should never be heated as they have low smoke points.
Other oils, such as sunflower and safflower, can be heated to high temperatures without harm (and perhaps most importantly, without combusting).
It is worth doing research to find the right oil for the job by looking at the smoke point of each oil. Cold-pressed seed oils processed without heat or chemicals are on the market along with sustainably harvested, non-GMO oils.
Need an Oil Change?
First, check the oil. The optimal daily amount of oil is about 2 Tbsp in a 2,000-calorie diet. Read food ingredient labels and see how much oil is in packaged foods.
Then, make decisions. There are different oils for frying, baking, and dipping to avoid setting the kitchen on fire and to obtain desired flavor.
If chemical extraction and highly processed oils are worrisome, pay more for cold extracted, pressed, and unrefined oils.
The debate over seed oils will likely sizzle until clinical trials provide scientific evidence to inform people of the health effects of these oils.
The debate over seed oils will likely sizzle until clinical trials provide scientific evidence to inform people of the health effects of these oils.
If the lack of research on seed oils is daunting, there are fruit, nut, and animal oils that have been better researched and can round out a cooking repertoire. For even more information on shopping for and using oils, “The New World of Cooking Oils” published in Consumer Reports Magazine does a deep dive on how and when to get the best deals.
Homemade Oils
There is no need for shopping tips for those who make their own oils at home! (Don’t make that face, people have been doing it for 8,000 years!) Fortunately, modern kitchen machines make it a breeze. Manual oil presses are less than $100. Electric expeller presses start at around $200.
No matter where anyone looks, there is conflicting information on oils, but dietary fats are essential for body functions. Spend some time in the oil aisle and try a healthy, new ingredient.
Recipes:
Fried Green Tomatoes
4-5 servings
This refreshing early season recipe is a delicious lunch or side dish. Substitute lemon-pepper for the chili powder for a less spicy, tangy flavor.
Ingredients
4 medium, firm green tomatoes
salt
1 cup flour of choice
1 Tbsp chili powder
1 tsp paprika
½ cup milk of choice
1 egg
1/3 cup fine cornmeal
½ cup crushed crackers of choice
¼ cup peanut oil
Process
Slice tomatoes into ½ inch slices and sprinkle each with salt. Set aside. Use 3 shallow bowls for dredging. In bowl 1, mix flour and seasoning. In bowl 2, whisk milk and egg. In bowl 3, combine cornmeal and crackers.
Heat the oil in a skillet on medium heat. Dip the tomato slices in the flour, then the egg, then the cornmeal. Place as many slices as will fit in one layer in the pan and fry for 3 to 5 minutes on each side or until brown and crispy. Drain on a towel. Enjoy.
Roasted Tri-Color Carrots
A flexible and tasty recipe. Make as much as will fit on your baking sheet. You won’t mind having leftovers. The sugar in the carrots caramelizes and will make a carrot lover out of anyone. Tri-color carrots aren’t necessary but the flavors are more interesting.
Process
Rinse carrots, cut in half, and then slice lengthwise into thin sticks.
Drizzle grapeseed oil on baking sheet.
Place carrots in one layer and drizzle oil on carrots.
Season lightly with salt, basil flakes, and garlic powder (or preferred seasoning).
Roast in oven at 425F for 20 minutes or until slightly browned.
Serve as a side dish or snack. Refrigerate leftovers (they are good cold, too).
*Julie Peterson is a freelance journalist based in the Midwest region of the US who has written hundreds of articles on natural approaches to health, environmental issues, and sustainable living.