What's the Deal With Seed Oils—Are They Really So Bad for You?

Layered with controversy and conspiracy, seed oils as a cooking ingredient are a hotly debated topic within the health and nutrition space. Some warn that seed oils are toxic and extremely detrimental to our health—a quick search on TikTok will bring you straight to an endless feed of videos claiming that “seed oils are toxic”. Others reason that there’s no hard evidence to support these kinds of claims. Is there a clear-cut answer here? Before slipping down this oily slope and throwing away the contents of your pantry, here’s what the research and nutrition experts have to say about whether or not seed oils are as bad for you as you may have heard. 

What Are Seed Oils?

Seed oil is an umbrella term for a variety of vegetable-based, oftentimes refined oils. These include canola, soybean, corn, cottonseed, grapeseed, safflower, sunflower, rice bran, and peanut oils. All are typically created through synthetic chemical extraction methods that sometimes include additional processing like bleaching and deodorizing.

Do Seed Oils Offer Nutritional Benefits?

They’re not the most nutrient-dense choice.

When looking at seed oils from a nutrition perspective, the profiles across the different kinds are quite similar. Seed oils are a pretty high-calorie food without providing much in the way of nutrients, given that 1 tablespoon provides more calories than 3 ounces of smoked salmon, a cup of edamame, or ¹/₃-cup of ice cream. Whether it’s canola, safflower, generic “vegetable oil,” or another variety, 1 tablespoon of seed oil will provide approximately 120 calories, no protein or carbohydrate, and about 14 grams of fat. Also, some will have additional ingredients including soy lecithin, TBHQ (a preservative), and mystery additives that are extremely hard to pronounce, like dimethylpolysiloxane. 

They’re higher in inflammatory fats.

One of the key aspects of the seed oil debate is their fat composition. Seed oils are a high-fat food—a label that we now generally understand isn’t always synonymous with “unhealthy”—but the kind of fat these oils contain is important to highlight. When looking at the different types of fatty acids, omega-3s tend to get a lot of positive press: They’re anti-inflammatory fats that can help reduce risk of chronic illness and improve heart health. Omega-3’s less-good-for-you counterpart, however, is omega-6 fatty acids, and most seed oils are predominantly composed of omega-6 polyunsaturated fats. These types of fat are widely considered to be inflammatory fats. 

While it’s important to reduce chronic inflammation in our bodies, inflammation does serve us in notable ways, and we actually need some of both kinds of fats. (When we experience physical, chemical, or heat trauma, the inflammatory response that our bodies carry out helps prevent damage from spreading to nearby tissues, works to remove cellular waste and pathogens, and springs the healing process into action.)

That said, over the last 50-plus years, consumption of omega-6 fatty acids has skyrocketed, especially in America, increasing 2.5 times from 1959 to 2008. The ideal omega-6-to-omega-3 consumption ratio is roughly 4:1; meanwhile, American consumption of omega-6s to omega-3s can be anywhere from 20:1 to upwards of 75:1. This throws the delicate balance of pro-inflammatory and anti-inflammatory fats in our body way off and can possibly lead to unnecessary inflammation in our bodies.

The Pros of Seed Oils for Cooking

Seed oils do offer some advantages in the kitchen. These highly processed oils offer a neutral flavor that will last for a long time in your pantry—and they’re extremely easy on the wallet. 

They also have a high smoke point, the temperature at which an oil literally starts to smoke. When an oil begins to smoke, the enzymes, minerals, and other compounds in it start to break down and release free radicals. Free radicals are unstable atoms that can cause significant damage and inflammation to cells, leading to minor inconveniences like wrinkles all the way to life-changing diagnoses like cancer. What’s more, when oils are heated beyond their smoke point, a substance called acrolein is created, giving off the acrid taste and aroma of burnt food. When you’ve reached the smoke point while cooking, you’ll know it: Your eyes will be watering, your nostrils will be burning, and your dog will be quivering in the corner from the sound of smoke alarms.

Many seed oils’ higher threshold for heat makes them optimal for frying and high-heat cooking methods like roasting and sautéeing. And the processing that enables these oils to have long shelf lives and higher smoke points make them optimal ingredients for other processed foods, made to last long enough to see you through the apocalypse.

Are Seed Oils Toxic or Dangerous for Health? Here’s What the Research Says

So are seed oils as bad for you as the social media nutritionist you follow claims? When it comes to the science on this topic, things get a little complicated, and the jury is still out on a definitive yes or no answer. 

Some studies have linked nutrients found in seed oils to poor health outcomes. 

One systematic review looking specifically at the omega-6 fatty acid linoleic acid, found that there was a positive correlation between linoleic acid concentration in fat tissue and diabetes, obesity, asthma, and coronary heart disease. Another review found that increased omega-6-to-omega-3 intake is correlated to increased risk of obesity.

But other studies’ findings aren’t so damning or definitive.

On the other hand, one meta-analysis of four different randomized control trials, amounting to 660 participants, found there was insufficient evidence to determine that omega-6 fatty acid intake had a positive or negative effect on both cardiovascular disease outcomes and risk factors like elevated blood pressure or lab values. A review from 10 years earlier was also unable to determine any absolute correlation between increased omega-6-to-omega-3 intake and heart disease. A further meta-analysis looking at 30 studies encompassing results from over 1,377 participants found that increased dietary linoleic acid did not have any significant impact on blood levels of inflammatory markers. This review concluded the same results. And this study even found that omega-6 fatty acid intake was actually associated with lower levels of bodily inflammation.

What’s more, Harvard’s School of Public Health has published its stance on the topic, citing that science tells us there is no concrete evidence to support seed oils being toxic substances that should be avoided at all costs.

Bianca Tamburello, RDN, a registered dietitian at FRESH Communications, echoes this sentiment. “Critics caution that the omega-6 fatty acids found in seed oils can cause inflammation; however, there isn’t enough research to support the recommendation to stop eating seed oils,” she says. “In comparison, there is a wide body of research that supports that polyunsaturated fats, like omega-6 fatty acids, support health by lowering cholesterol and contributing to better blood sugar control.”

Where Do We Go From Here?

With all this conflicting information, what food choices should you make when it comes to seed oils? The bottom line is that these oils aren’t necessarily the all-time healthiest option to cook with and consume in excess. But there’s no reason to panic and banish seed oils from your pantry and recipes altogether. That said, here are some helpful nutritional rules of thumb to abide by when it comes to using seed oils:

Moderation is the name of the game.

Using whole sources of seed oils in moderation—like whipping up a stir fry with a bit of canola oil or using some sunflower oil in baked goods—is definitely not going to endanger you, and may be a better-for-you alternative than something like bacon grease or shortening.

Opt for omega-3-rich oils when you can.

If you want to up your oil game and include more omega-3s into your meals, for olive oil or avocado oil. These are some of the healthiest oil options that have been linked to improved heart health, among other nutritional benefits. Plus, avocado oil has an added bonus of a high smoke point!

Limit processed food and packaged products that contain added seed oils.

“Seed oils are found in most processed foods such as chips, baked goods, and crackers,” Tamburello explains. “I recommend limiting these processed foods that are often high in added sugar, sodium, and fat—but [I don’t recommend cutting out] whole sources of seed oils.”