How bad are seed oils, really?

In 2023, a trendy salad spot announced it would remove something called seed oils from its kitchens. And while many people scratched their heads (“what the heck are seed oils?”), the movement against them was well underway. Labels and seals touting “seed oil free” started appearing in grocery aisles. Podcasts started covering them as the food enemy du jour. And — long before he took over the U.S. Department of Health and Human Services — Robert F. Kennedy Jr. called seed oils toxic. So, have they earned such vitriol or is this just a case of mistaken ingredient identity? Here’s what the research and the credentialed experts say.

What are seed oils?

“Seed oils are oils that come from seeds, such as canola, sunflower, safflower, and sesame. Corn and soybean oils are also considered seed oils,” says Fernanda Almeida, RDN, a registered dietitian at WeightWatchers. They’re often listed as an ingredient in packaged foods, such as cookies and frozen dinners, and they’re used on their own for cooking and baking at restaurants and at home.

While all fat sources — oils included — contain a blend of fats in different ratios, seed oils are primarily made of unsaturated fats. (In contrast, the most plentiful type of fat in butter is saturated fat.) And that’s actually a good thing, says Almeida. “Because seed oils are high in unsaturated fat and low in saturated fat, they are considered heart-healthy, especially when you use these oils to replace oils and fats higher in saturated fat,” says Almeida. In fact, the American Heart Association lists canola, corn, safflower, soybean, sunflower, and vegetable oil as cooking oils that are in the “healthy” category for this reason.

Why seed oils got a bad rap

They come from natural sources, they’ve got heart-healthy fats. So, what’s the problem? Recently, people — e.g. healthfluencers — started making posts correlating seed oil consumption with rising rates of chronic disease, thus attributing diseases like obesity to these oils. However, there’s an inherent flaw in this logic: “This shows correlation, which in no way proves causation,” says Almeida. “I bet you could link those outcomes with smartphone or computer use, but just because you own a smartphone does not mean you will have obesity,” she says. (Not to mention that some seed oils, like sesame, have been used for thousands of years.)

The reality is that research shows the opposite when it comes to seed oil and health: “Using more of these seed oils in place of higher saturated fat products like butter, lard, beef tallow, coconut oil, or palm oil leads to improved cardiovascular health, in particular lower risk of high cholesterol and heart disease,” says Almeida. One review, published in the British Journal of Nutrition in 2024, illustrates this, showing that replacing saturated fats with unsaturated fats improves lipoproteins and doesn’t increase inflammation. It also shows that consuming more of a specific type of unsaturated fat — polyunsaturated fat — is associated with a lower risk of coronary artery disease, cardiovascular disease mortality, and type 2 diabetes.

The real trouble with seed oils

The oils themselves are good — they just aren’t always used in good ways. “It’s important to acknowledge the bigger picture. Seed oils are often most ubiquitous in packaged, ultra-processed foods, and fried or fast food,” says registered dietitian Lisa Moskovitz, R.D., founder of the NY Nutrition Group. “These are foods that are okay to consume occasionally, but will never be the healthiest choice, nor are they recommended as regular staples in your diet.” In addition to seed oils, ultra-processed foods also tend to have excess sodium, saturated fat, and added sugar, three things that are connected to health risks like hypertension, high cholesterol, metabolic disease, obesity, and inflammation. UPFs are also often higher in calories that may promote weight gain.

“What seems to be pretty clear is that it's those components — not the seed oils themselves — that are problematic. The key with ultra-processed foods is that they no longer have whole foods in them, and they contain additional chemical additives,” adds Almeida. “Being higher in fat, sugar, and sodium, our bodies have adapted to wanting more of these foods, which can make it hard to control our consumption of them,” she says.

If you do single out seed oils and actively avoid them in your diet, you may end up consuming less of these ultra-processed foods and eat more whole foods, which may help improve your health. On the flipside, if you replace a seed oil with another type of fat, you do not automatically make that a healthy food. “It depends on the type and quantity of fat in the product,” says Moskowitz. “There are many other seed oil substitutes that can be more problematic for heart health in large quantities.”

One example of this is fried fast food prepared with beef tallow, which is an animal-based fat that’s higher in saturated fat. Regardless of the frying oil used, the food is still fried — possibly adding hundreds of calories and a lot of excess sodium.

The best oils and fats to cook with, according to dietitians

One thing you can do to make a measurable impact on your health is to reduce your intake of ultra-processed foods (which includes fast food). In addition, try cooking more food at home, which has been linked to lower body fat and overall health (and is budget-friendly, too). When you cook at home, you have control over what fats you use. “Extra virgin olive oil and avocado oil will always be the most optimal fats to use for cooking because they are highest in anti-inflammatory and cholesterol-lowering monounsaturated fats,” says Moskovitz.

For weight management, keep in mind that all cooking oils are similar in calories and fat, so portion size matters, Moskovitz says. One tablespoon of olive oil, canola oil, and avocado oil has about 120 calories. (Butter has about 100 calories in a tablespoon.) “There are reasons to choose an unsaturated fat like a seed or olive oil over butter. However, it’s important to be mindful of the amount you’re consuming — no matter what type of oil or fat it is,” says Almeida.

The bottom line

Seed oils include oils such as canola, sunflower, safflower, and sesame. Although social media has pegged these as inflammatory ingredients that promote weight gain and chronic disease, scientific data suggests otherwise. Research shows that when you substitute sources of unsaturated fat, which includes seed oils, for sources of saturated fat, such as butter or lard, measures of cardiometabolic health like lipid levels improve. However, seed oils are often found in ultra-processed foods, and overconsumption of these are harmful for health, as they’re often sources of added sugar and sodium. Choose avocado and olive oil for cooking when you can, since these are best for heart health; however, using seed oils when needed is OK too.