What You Need to Know About Seed Oils, According to A Dietitian

August 7, 2024

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Depending on which corner of social media you wander into these days, you’ll either hear that seed oils are perfectly fine and healthy, or they’re completely toxic and killing us all. In fact, there’s a whopping 20 million TikTok videos dedicated to the topic.

People who are anti-seed oils blame them for causing a slew of health issues including cancer, chronic inflammation, diabetes, obesity, and heart disease. At the same time, these oils are everywhere — in all kinds of snacks, packaged nut butters, dairy-free spreads and beverages, and even mixed into olive oil. Plus, most restaurants cook in them.

So, are seed oils perfectly fine, or to be avoided at all cost? As you might expect, the answer isn’t that simple.

What oils are considered seed oils?

As you may have guessed, these oils come from various types of plants and their seeds. Because of their neutral taste, high smoke points, and affordability, seed oils have become ubiquitous, particularly in restaurants and packaged foods like chips, cookies, and salad dressings.

Seed oils are polyunsaturated fats (PUFAs), with most classified as omega 6 fatty acids and some as omega 3 (the same healthy fat found in fish).

There are a number of different types, but these are the most common, sometimes called the “Hateful Eight”:

Canola
Corn
Safflower
Sunflower
Cottonseed
Grapeseed
Soybean
Rice bran

Are seed oils bad for you?

There are two issues with them: One involves how they’re made, and the other lies in the omega 6 fatty acids they have.

“Not all seed oils are bad. The health impact of seed oils is related to the fatty acid profile and a few other factors, like how easily the oil is extracted and how much refining is required,” says Shana Hussin, RDN.

In terms of how they’re made, most seed oils are ultra-processed. Commercially refined oils are typically filtered, bleached, and heated, and, as a result, stripped of most of their health benefits. Also, because of their chemical makeup (PUFAs have double bonds), they’re highly unstable and susceptible to oxidation when exposed to heat, light, and chemical solvents. Oxidation not only can turn oil rancid, but it also can create harmful compounds that may be carcinogenic. Commercially produced seed oils are heated during processing and then again during cooking, which degrades them even further.

The other issue is the omega 6 fatty acids. Omega 6s aren’t bad; in fact, research has found that they have several health benefits, like lowering risk of stroke and heart disease. The problem arises with the ratio of omega 3 to omega 6 we consume in our modern diets now that seed oils are everywhere.

Research suggests that humans had a ratio of 4:1 omega 6 to omega 3 until about 100 years ago. Nowadays that ratio is more like 20:1 or higher, and the excess of omega 6s relative to omega 3s can cause chronic inflammation and potentially a host of lifestyle diseases like type 2 diabetes. So although seed oils are deemed GRAS (generally recognized as safe) by the FDA, it matters how much of it you take in.

How to (realistically) limit them

Completely avoiding seed oils may be close to impossible, given how ubiquitous they are, but there are steps you can take to limit your consumption.

Read food labels. Look for products that contain healthier types of fats. If you do see a seed oil, note where it is on the ingredient list. The higher up on the list it is, the more of it is in the product.
Take care when dining out. When eating in restaurants, ask if you can have your food cooked in butter or extra virgin olive oil, if possible. Avoid fried food, since deep-fryers typically use seed oils, and the oil is used repeatedly. That regular reheating makes its quality deteriorate even further.
Look for seed oil–free restaurants. Thanks to concerns about seed oils, some restaurants don’t use it or make a point of offering alternatives. Hussin recommends the Seed Oil Scout app, which lists seed oil–free restaurants.
Cook with other fats. You always control the fats you cook with at home, so you can avoid seed oils there, or choose less processed ones that are cold-pressed (without heat or chemicals) or expeller-pressed (without chemicals). Hussin recommends using extra virgin olive oil, grass-fed butter, clarified butter (ghee), extra virgin coconut oil, avocado oil, or animal fats like bacon fat, duck fat, lard, or tallow for cooking. For sauces and dressings, she also recommends macadamia nut oil, almond oil, and sesame oil.

“Avoiding the ‘hateful eight’ will remove the unstable PUFA from your diet, detoxify your body, and help you to reclaim metabolic health and flexibility,” Hussin says. “Remember, it’s the processing of the seed oils themselves that create all these issues, not the actual seeds of the plant.”