Are Seed Oils That Bad For You? Here's How Nutritionists Think About Them
Over the past century, the consumption of seed oils—also known as vegetable oils—has skyrocketed. Scientists warn that modern-day diets are much too high in these fats and that our overreliance on them may be harming our health.
But how harmful are seed oils, and do we need to avoid them altogether? This article breaks down the science behind seed oils—the good, the bad, and the ugly—to help you decide what role they should play in your diet.
What are seed oils?
"Seed oils" is a blanket term used to describe omega-6-rich vegetable oils that are made from seeds. Soy and canola oils are also referred to as seed oils, even though they don't come from seeds.
Food manufacturers and restaurants began to rely heavily on seed oils in food production decades ago, as Americans moved away from animal-based fats like butter and lard in order to protect heart health and save money.
According to scientists and physicians in the field of lipid research, the following seed oils may be the most problematic for health:
- Soybean oil: Soybean oil, which is different from soy-based food products (tofu, edamame, etc.), is derived from soybeans and is the most common vegetable oil in U.S. diets. This fat makes up over 60% of the vegetable oil in U.S. diets3. The omega-6 fat linoleic acid makes up around 55% of this oil.
- Canola oil: Canola is the second largest oil crop in the world, and over 90% of canola crops4 grown in the U.S. are genetically modified to increase plant tolerance to herbicides like glyphosate5. Canola oil is composed of 21% linoleic acid.
- Corn oil: Corn oil is a main dietary source of linoleic acid.6 Linoleic acid makes up around 34 to 62% of the fats in corn oil. It's commonly used in the restaurant industry to deep-fry foods.
- Cottonseed:Cottonseed oil is made from the seeds of the cotton plant. It's high in linoleic acid, which makes up over 50% of this fat. It's used as a cooking oil and in products like salad dressings.
- Safflower oil: Safflower oil is derived from the seeds of the safflower plant. It's one of the richest sources of omega-6 fats, with an omega-6 to omega-3 ratio of 77:1.7 You can find safflower oil in salad dressings, butter replacement products, and snack foods like chips.
- Sunflower oil: Sunflower oil is produced from sunflower seeds and is one of the most popular oils used for cooking. It contains up to 70% linoleic acid by weight, so it's a major dietary source of omega-6 fats.
The health concern with seed oils.
The problem with seed oils is that they're found in many foods and are some of the most common fats used for cooking. Because of this, they make up the majority of fats in most people's diets.
According to research, there are a few ways in which our overreliance on seed oils is thought to harm health:
They disrupt the omega-6 to omega-3 ratio.
"Seed oils have a higher omega-6 content than other, healthier fat options. The evidence isn't conclusive whether or not omega-6 fats are always inflammatory in a 'bad' way. It is clear that we need them but in lesser amounts than their anti-inflammatory omega-3 counterparts," Whitney Crouch, RDN, CLT, tells mindbodygreen.
Even though the ideal omega-6 to omega-3 ratio isn't yet known, experts believe it should lie between 1:110 and 4:16 for optimal health. Unfortunately, the average American diet contains up to 20 times more7 omega-6 fatty acids than omega-3 fatty acids, which can promote inflammation in the body and may contribute to inflammatory diseases.
They're highly processed.
Seed oils like canola oil (also known as rapeseed oil) go through a refining process, including bleaching and deodorizing, that helps improve the taste and color of the oils and extends their shelf life. Unfortunately, the refining process strips oils like canola oil of beneficial compounds like vitamin E and phenols11, meaning they're less nutritious than unrefined oils.
They're often genetically modified.
They're prone to oxidation.
Many seed oils have a high smoke point, meaning they can be heated to a high temperature without burning. However, some are high in polyunsaturated fats (PUFAs), which makes them prone to oxidation—a reaction between fats and oxygen that causes the formation of harmful compounds14 like free radicals.
Again, while occasionally enjoying french fries or using a salad dressing made with canola oil won't harm health, regularly consuming omega-6-rich seed oils and the ultra-processed foods they're often used to make (and not consuming adequate amounts of anti-inflammatory omega-3-rich foods), could contribute to health issues.
The benefits of seed oils.
Even though seed oils are linked to some significant concerns, they're not all bad. Here are some seed oil benefits to consider:
Unrefined versions contain protective nutrients.
Nearly 90% of U.S. adults16 fall short of the RDA for vitamin E, so using an unrefined seed oil could help people meet their needs. That said, there are plenty of other sources of vitamin E to choose from, so you certainly don't need to include these oils in your diet if you're looking to bump up your vitamin E intake.
Some seed oils have a high smoke point.
A smoke point refers to the temperature at which an oil begins to smoke. The refining process that most seed oils go through makes them more stable at high temperatures17, which is why they're commonly used in recipes that call for frying. Refined oils also have a mild taste profile, which is desired in food production.
Are seed oils inflammatory?
Seed oils like safflower oil, canola oil, and soybean oil are high in the omega-6 fat linoleic acid and have low proportions of omega-3 fats. The body needs both omega-3 and omega-6 fats, but most people consume way too many omega-6-rich foods and not enough omega-3-rich foods.
Scientists are still studying the relationship18 between omega-6 and omega-3 fats and their role in inflammation, which is highly complex and not black and white. Also, although there's a general agreement in the nutrition world that most diets are too high in omega-6 fats, there's no definitive consensus18 on what the optimal omega-3 to omega-6 ratio should be.
While it's true that omega-6-rich diets may harm health by promoting an inflammatory environment in the body, the real problem isn't omega-6 fats. According to Crouch, "While eating something with seed oils every once in a while won't strike up an inflammatory disease process, we need to pan out and view the big picture," she says.
The major issue with Western diets is that they tend to be high in inflammatory ultra-processed foods and deficient in omega-3 fats—and a number of other nutrients—which regulate inflammation in the body.
If you're concerned that your intake of omega-3s is too low and your intake of omega-6 foods, like seed oils, is too high, try reducing your intake of ultra-processed foods and increasing your intake of seafood. If you don't like fish or follow a plant-based diet, taking an algal oil supplement can help you increase your DHA and EPA intake.
So, should I avoid seed oils?
As with all other foods, it's not a good idea to demonize seed oils. "I don't believe in demonizing foods or putting anything completely off limits, but I do make an effort to steer clients toward less refined, nutrient-dense oils that offer research-backed health benefits," Jessica Cording, M.S., R.D., tells mindbodygreen.
So if your current diet contains omega-6-rich foods, like seed oils, don't stress. "If refined seed oils are an occasional or small part of your diet, I would tell someone not to freak out about that," says Cording. "However, if you're eating a lot of processed foods that contain seed oils or are dining out frequently where seed oils may be more commonly used, that's when you'd want to swap out some of those foods for less processed items that utilize healthier oils."
Cording also recommends cooking more at home and being intentional about working more sources of omega-3s into your day.
Crouch agrees and recommends focusing on your overall dietary intake. "I advise clients to focus on consuming nutrient-dense foods like high-quality fruits, vegetables, and protein sources. When we focus on eating foods closer to nature, we naturally reduce our intake of processed seed oils and nutrient-poor food options," she says.
As for which oils to use in your home cooking, both dietitians agree that nutritious options like olive oil and avocado oil make smart choices.
"I generally recommend making extra-virgin olive oil and avocado oil your primary cooking oils," says Cording. Diets rich in olive oil are consistently linked with improved health outcomes19 like lower rates of heart disease, Type 2 diabetes, and obesity, while avocado oil is rich in antioxidants like lutein and carotenoids.
Guidelines for healthy oil consumption.
Here are a few more tips that can help you make healthier choices when it comes to cooking oils:
- Choose healthful oils like olive oil and avocado oil over highly refined seed oils like canola and soybean oil whenever possible.
- Cook more meals at home so you know exactly which fats are being used to prepare your meals and snacks. Preparing more meals at home will also help you cut back on your intake of highly processed foods, which often contain seed oils.
- Transition to a whole-foods-based diet that's low in ultra-processed foods made with omega-6-rich seed oils.
- Use the right kinds of oils for the right cooking temps. Olive oil20 is a perfect choice for sauteing on medium heat, while avocado oil and refined coconut oil are better for high-heat cooking like pan-frying because they're more stable at high temperatures21. Use oils with a low smoke point, like sesame oil and pumpkin seed oil, for drizzling on salads and adding flavor to dishes after cooking.
- Remember, it's your diet as a whole that matters most when it comes to disease prevention and helping you feel your best. If your diet is nutrient-dense but includes small amounts of seed oils, that's A-OK in the opinion of most health experts.
Frequently Asked Questions
Why are seed oils bad for you?
Seed oils aren't inherently "bad" for you, but if you eat too many omega-6-rich foods—like seed oils and ultra-processed foods—and not enough omega-3-rich foods, it could contribute to an inflammatory environment in the body. To promote optimal health, it's best to limit your intake of omega-6-rich foods like seed oils and consume mostly whole, nutrient-dense foods whenever possible.
Is olive oil a seed oil?
Olive oil comes from olives, so it's not considered a seed oil. All seed oils are considered vegetable oils, but not all vegetable oils are considered seed oils.
Which oil is the healthiest?
Olive oil is a fat that's linked to a number of health benefits. Research shows that diets rich in olive oil reduce the risk of health conditions like heart disease, obesity, and high blood pressure. Plus, diets high in olive oil, like the Mediterranean diet, are associated with a longer and healthier life span. Extra-virgin olive oil is the most recommended oil by health experts—often followed by avocado oil.
Modern-day diets tend to be too high in omega-6 fats and too low in omega-3 fats. Experts suggest that this imbalance drives systemic inflammation and increases inflammatory disease risk. Seed oils like soybean oil, canola oil, and safflower oil are major contributors to omega-6 intake in most people's diets because they're found in a number of ultra-processed foods.
For most people, shifting to a dietary pattern that prioritizes nutrient-dense foods and limits the use of seed oils is best. As for the most nutritious cooking oils to embrace, here's a comprehensive guide to the top eight.
Jillian Kubala, MS, RD is a Registered Dietitian based in Westhampton, NY. She holds a master's degree in nutrition from Stony Brook University School of Medicine as well as an undergraduate degree in nutrition science.
In addition to her private practice where she uses a unique and personalized approach to help her clients achieve optimal wellness, she works as a freelance writer and editor and has written hundreds of articles on nutrition and wellness for top digital health publishers.
Jillian and her husband have a backyard farm where they grow their own food and keep chickens. She runs a small cut flower business specializing in organically grown dahlias.