Can Seed Oils Really Cause Inflammation and Damage the Gut? Experts Talk Through the Health Claims

Critics have dubbed seed oils as the “hateful eight,” according to Elena Ivanina, DO, MPH, founder of The Center for Integrative Gut Health. This includes oils made from canola, corn, sunflower, safflower, soybean, grapeseed, rice bran, and cottonseed, she says. According to some, seed oils (which are found in high amounts in ultra-processed foods) are harmful due to their fatty acid content and super-processed nature.

But here’s the thing: These claims, like many health allegations on the web, fail to provide context. To learn more, we spoke to health experts about seed oil myths and why such claims might not be what they seem.

What are seed oils?

Seed oils is an umbrella term for refined, vegetable-based oils that are extracted from only the seed portion of a plant. Examples of seed oils include canola, corn, sunflower, safflower, soybean, and sesame. (Olive oil, coconut oil, and avocado oil are vegetable oils, not seed oils.) In seed oils, the oil is typically first extracted through mechanical means (an expeller press), and then chemical means (solvent extraction that might use hexane). And despite some internet rumors, no, seed oils are not banned in Europe.

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What are the claims about seed oils—and what do experts say?

Claim #1: The fats in seed oils cause systemic inflammation

There is some merit to this claim, but it’s oversimplified at best.

Seed oils contain both omega-3 and omega-6 fatty acids, explains Matthew Bechtold, MD, a gastroenterologist at the University of Missouri. Omega-3 fatty acids tend to have anti-inflammatory effects, while some omega-6 fatty acids tend to have pro-inflammatory effects, he says. And while seed oils, like black seed oil, are generally higher in omega-6 versus omega-3, it doesn’t necessarily mean they’ll directly lead to inflammation.

Here’s the deal: The most common omega-6 (linolenic acid) turns into another fatty acid (arachidonic acid) in the body. Arachidonic acid can cause inflammation in certain settings, but it can also quell inflammation in others, says Dr. Bechtold. That said, it has many functions in the human body, so focusing on one of its effects (read: causing inflammation) is too simple, says Paula Doebrich, MPH, RDN, registered dietitian and founder of Happea Nutrition.

Additionally, the inflammatory reputation of omega-6 fatty acids is mainly based on mechanisms observed in animal studies, says Doebrich. “Luckily, our bodies are more complex than those of lab rats,” she notes. What’s more, human studies have found that higher intakes of omega-6 fatty acids aren’t shown to increase inflammation.

Claim #2: Our ratio of omega-6 vs. omega-3 is the problem

When arguing against seed oils, critics will often cite the issue of omega-6 versus omega-3 ratios in the American diet. However, this approach is highly generalized, as it doesn’t acknowledge the important role omega-6s can play in our nutrition. This includes their ability to lower LDL (“bad”) cholesterol and increase HDL ("good") cholesterol, which may help reduce the risk of heart disease, says Doebrich.

Now, it’s true that the average American diet has more omega-6 than omega-3 fatty acids (about 10 times more, in fact) due to the high intake of ultra-processed foods. It’s also true that excess intake of such foods can lead to chronic conditions, such as heart disease and diabetes.

“However, it’s not the level of omega-6 that’s the problem,” explains Dr. Bechtold. “It’s the low level of omega-3 fatty acids.” That’s why experts recommend eating more omega-3 fatty acids rather than reducing omega-6, from seed oils or otherwise.

Claim #3: Seed oils damage the gut

“There isn’t much research on seed oils and the gut, but this [claim] may be from the fact that many highly-processed foods are sources of seed oils,” says Doebrich. As mentioned, such foods can increase the risk of chronic disease, as well as overall inflammation. They can also lead to digestive issues such as Crohn’s disease, according to Dr. Ivanina.

That being said, seed oils are not the cause of these problems, says Doebrich. Ultra-processed foods contain other components, like added sugars, excess sodium, and refined carbs. They also typically lack essential nutrients for a healthy gut, such as fiber. Not to mention, other ultra-processed foods sans seed oil (like soft drinks and processed meat) can also cause the aforementioned health issues, says Dr. Ivanina.

But what about the folks who say their gut feels good after ditching foods with seed oils? “The truth is, when you cut back on highly processed or deep-fried food, you will feel better,” says Doebrich. Dr. Bechtold agrees, adding that whether or not you eat seed oils has little to do with feeling good. Instead, it’s more about replacing foods that have little nutritional value with whole foods like fruits and vegetables, he says. And that's more often than not exactly what happens when you stop eating seed oil.

Claim #4: Seeds oils have harmful chemicals

Another claim is that seed oils contain toxic compounds—but again, this is only one piece of the puzzle.

According to Doebrich, manufacturers use a process called solvent extraction to isolate oils from seeds. This process might use hexane, a chemical that helps pull oil out of seeds. And though hexane is harmful at high exposures or when inhaled, seed oils contain little residual hexane. (Worth noting, most of our hexane exposure is from gasoline fumes, not from foods, adds Doebrich.)

The claim might also be related to the high temperatures that seed oils are often cooked at, rather than the oils themselves. According to Doebrich, when oil is heated at high temperatures for a long time, the beneficial unsaturated fats can turn into trans fats or “bad” fats. But this isn’t a huge concern in the average home kitchen, where oils aren’t usually heated at high enough temperatures (or long enough times). Instead, it’s more likely to happen in scenarios where oil is being consistently reused at scorching hot temps, like in commercial kitchens.

Are there any real risks or negative effects?

Okay, so it's clear that the claims going around the web about seed oils are simply internet rumors. But is there any reason you would want to avoid these oils? The short answer: no. "There isn't significant evidence that seed oils are harmful," says dietitian Erin Davis, RDN. "The oils themselves are inexpensive when compared to olive and avocado oil, and can be used interchangeably."

There aren't any particular seed oils to avoid, according to these experts. But if you are looking to amp up the nutritional value of the oils in your kitchen pantry, Davis recommends investing in cold-pressed options. "They are less processed than conventional seed oils," she explains, adding that this means they keep more of their natural vitamins, minerals and antioxidants. "Oils that are highly refined do not retain as many health-promoting compounds."

Yes, seed oils do have some nutritional benefits

Not only do you not need to throw out your bottles of canola oil, the truth is that seed oils can positively contribute to a healthy diet. As mentioned, seed oils do contain omega-3 fatty acids, which have anti-inflammatory effects.

"Diets that include seed oils, like the Nordic diet, can reduce low-grade inflammation and [decrease] the risk for diabetes and cardiovascular disease," says Davis.

One seed oil that's actually considered a "superfood" is black seed oil, which is high in antioxidants, can reduce oxidative stress, and has been shown to be good for respiratory health, among several other benefits. (That doesn't sound so bad now, does it?) And FWIW, flaxseed oil has long been known to be excellent for skin health.

The best ways to use seed oils for cooking

Seed oils are often must-have ingredients in chef's kitchens because they have a high smoke point, which simply means they can be heated to high temps before they start to smoke (and lose their enzymes, minerals, etc). They also last a long time before going bad, and are far cheaper than olive oil or butter.

"Seed oils are quite versatile—you can use [them] in any dish," says Davis. "And seed oils like canola oil are flavorless so you may prefer to use it for baked goods."

So, should I stay away from seed oils?

Bottom line: There’s no hard evidence that the current seed oil claims are valid, says Doebrich. Dr. Bechtold echoes this notion, expressing that there’s no reason to be concerned about seed oils and gut health in particular.

“The current recommendation is to make polyunsaturated fatty acids [like omega-6 fats] part of the diet because we know they are health-promoting,” explains Doebrich. This can be done by following a generally balanced diet, something that will naturally include seed oils in a healthy and recommended amount.

Still, as seed oil claims continue to take over social media, it’s crucial to remember that nutrition science is far from simple. And when a single food is demonized or shunned, the rhetoric around it typically disregards its complex relationship with different nutrients, biological processes, and individual bodies. Furthermore, overall health isn’t defined by eating (or omitting) any one food—no matter how conclusive some statements might seem.

Up next? Settling the canola oil vs. olive oil and "is rapeseed oil healthy" debates once and for all.