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.

"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.

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.

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.

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

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.

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.

Omega-6 fats are usually considered more pro-inflammatory, while omega-3s are considered anti-inflammatory. However, researchers argue9 that because fats are complex compounds that have different effects on the body, oils can't be perfectly placed into "good" and "bad" boxes.

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. 

The omega-3s EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)—which are readily used by the body—are concentrated in seafood9 like salmon, sardines, anchovies, and rainbow trout, as well as algae.

Omega-3s can also be found in foods like walnuts and hemp seeds, but the type of omega-3 found in these foods is poorly converted into DHA and EPA, making seafood and algae the best sources of these important fatty acids. 

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.

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.