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. 

"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.

Today, seed oils make up around 10% of calorie intake1 in the average American diet. These oils can be found in everything from infant formula to your favorite salad dressing. 

Although many health organizations like The American Heart Association2 promote the use of seed oils like soybean oil and sunflower oil over animal and plant-based fats that are high in saturated fats, health experts have identified major issues with some of the most commonly used vegetable oils.

According to scientists and physicians in the field of lipid research, the following seed oils may be the most problematic for health:

Most of these oils are used in home and restaurant cooking as well as in food production, so the average person consumes them on a daily basis. Grapeseed and rice bran oils are also of concern to some health experts, but they are not used in food production as often.

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:

Omega-6 fats and omega-3 fats are both necessary for health. However, while omega-3 fats are anti-inflammatory8, omega-6 fats tend to be more pro-inflammatory in nature9. 

"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.

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.   

Genetically modified organisms (GMOs)12 are among the most controversial topics in nutrition and environmental science.

Most crops used to make seed oils are genetically modified to improve resistance to harmful herbicides like glyphosate and improve crop yield. Scientists argue the increased use of herbicides like glyphosate on GMO crops13 can harm both human health and the health of the environment12. 

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.

These compounds can damage cells and contribute to inflammation in the body. Oils that are repeatedly heated15, such as oils used for deep frying in restaurants, are particularly susceptible to oxidation. 

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. 

Even though seed oils are linked to some significant concerns, they're not all bad. Here are some seed oil benefits to consider:

One of the biggest upsides of seed oils is their cost. Not everyone can afford higher-priced oils like olive oil and avocado oil, especially restaurants that need to keep food costs down. If you're on a budget, seed oils can be a much more economical choice compared to more expensive cooking oils.

While most seed oils are highly refined, there are unrefined versions of oils like canola oil and sunflower oil. Unrefined oils don't go through the same refining process as refined oils do. Because of this, protective compounds like vitamin E and phenols11 are maintained.

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.

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. 

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. 

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.

Here are a few more tips that can help you make healthier choices when it comes to cooking oils:

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.