Can Seed Oils Really Cause Inflammation and Damage the Gut? Gastroenterologists Talk Through the Health Claims
So much so that critics have dubbed seed oils as the “hateful eight,” according to Elena Ivanina, DO, MPH, director of neuro-integrative gastroenterology at Lenox Hill Hospital. This includes oils made from canola, corn, sunflower, safflower, soy, 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 the claims about seed oils—and what do experts say?
Claim #1: The fats in seed oils cause systemic inflammation
There’s 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 are generally higher in omega-6 vs. 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 (aka 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 vs. omega-3 ratios in the American diet. However, this approach is highly generalized, as it doesn’t acknowledge the important role omega-6s can provide. This includes its 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 vs. 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,” explains 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 with little nutritional value with whole foods like fruits and vegetables, he says.
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 Dobrich.)
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 (and 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.
So, do you need to avoid 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, it 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.
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