Are Seed Oils Really Bad for Your Health

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Seeds oils made from plants such as sunflower and canola have a bad reputation, but it's not really warranted. When used in small amounts - as oil is meant to be used - seed oils can be an important part of a balanced diet. They're also an essential source of omega-3 and omega-6 fatty acids.

Read on to learn what seed oils are, how much to consume, and which ones to choose for optimal health.

What are seed oils?

If you drizzle a ribbon of canola oil on salad greens or stir-fry your broccoli in sunflower oil, you're probably already familiar with seed oils. These culinary oils are made from pressed seeds, which naturally have a variety of fatty acids.

Seed oil is an umbrella term for oils that are made from seeds, such as:

• Sunflower

• Cottonseed

• Safflower

• Canola

• Grapeseed

But, most often the term also covers other vegetable oils that don't come from seeds - such as soy and corn oil. They all get grouped together since they share similar characteristics - they're extracted from vegetables, made into oil, and then used for home cooking and industrial food manufacturing. The latter use is the most problematic.

Are seed oils bad for you?

The idea that seed oils are bad for you is largely a myth. But where did the idea come from?

If you're active on social media, you may have seen infographics or TikToks that call out the "eight bad seed oils," which include:

1. Rice bran

2. Safflower

3. Sunflower

4. Corn

5. Canola

6. Cottonseed

7. Soybean

8. Grapeseed

Why are seed oils thought to be bad for you?

The idea that seed oils might be bad for you has been around for a while. Some scientists raised concerns because seed oils contain linoleic acid, which can be converted to arachidonic acid (AA). AA is known to be a pro-inflammatory molecule. But it turns out that only a very small amount is converted to AA. And studies in humans have shown that it's helpful, not harmful.

More recently, Cate Shannon, MD, wrote about "8 bad seed oils," or the "hateful eight." She referenced different studies that suggest a link between polyunsaturated fatty acids (PUFAs) - which are found in seed oils - and health conditions, like heart disease. But most evidence comes from small or animal and lab-based studies and isn't strong enough to draw any conclusions for humans.

Good to know: Like anything else in your diet, seed oils are fine in moderation. They should be part of an overall balanced eating plan that includes lots of vegetables, fruits, whole grains, and lean protein options.

Here are two big causes of concern when it comes to seed oils:

• Overuse: Seeds oils are a common ingredient in many ultra-processed foods, such as deep-fried foods, pastries, chips, and other crunchy fried snacks. These ultra-processed foods are also high in sugar, salt, and/or food additives. So, if you're consuming oil from these products, it can be partly to blame for the poor health outcomes.

• Repeated heating: Many restaurants reuse the same seed oils in their deep fryers. Heating seed oils to high temperatures time and time again is a problem. Reheating oil past its smoke point can create harmful compounds.

But cooking at home with seed oils - and using them once - isn't a health issue. In fact, omega-3 and omega-6 PUFAs in seed oils are an essential part of your diet. The Dietary Guidelines for Americans recommends a small amount of fat or oil daily. For an average 2,000-calorie Mediterranean-style diet, the Dietary Guidelines recommend about 27 g of oil per day (about 2 tbsp).

How much fat is in seed oils?

All seed oils are 100% fat. They're made up of a blend of different fatty acids, which are classified as monounsaturated fatty acids (MUFAs), PUFAs, or saturated fatty acids (SFAs). Each oil contains a different combination of fatty acids. The health value of oil also depends on the type of fatty acids that it contains.

Here's an overview of the fat content of select oils:

Overall, MUFA and PUFA are often prized for their health benefits, while saturated fats are often despised. But studies on saturated fats are mixed, and some specific saturated fatty acids are better than others.

Omega-3 and omega-6 fatty acids are types of PUFAs, and they're essential to your diet. Your body can't make enough of them on its own, so you need to get them through food. Canola and soybean oil have some omega-3 fats. Safflower, corn, and sunflower oil are mostly omega-6 fats.

Are seed oils inflammatory?

Experts need more high-quality evidence to be able to say for sure. Most seed oil research has been done on lab animals, such as rats. But there's little research in humans.

Since linoleic acid in seed oils can lead to pro-inflammatory markers, some scientists are concerned that a high intake of omega-6 fatty acids and a lower intake of omega-3 may be linked to several chronic diseases. But there are no compelling clinical studies to back up this theory. In fact, the opposite seems to be true.

So, what is known? One analysis of omega-6 linoleic acid in humans shows that it can protect against inflammatory diseases. The analysis found that those with higher amounts of omega-6 linoleic acid in their bloodstream were 7% less likely to develop heart disease. But this study was funded by Unilever, which historically made margarine and mayonnaise from seed oils. So possible bias is a concern.

Another study (with no biased funding) found that there's an association between moderate intake of omega-6 linoleic acid and lower risk of cardiovascular disease. Overall, the science suggests that omega-6 seed oils are beneficial rather than harmful or inflammatory.

Remember, oils are also made up of a mix of different fatty acids. So some seed oils may contain a mix of omega-3 and omega-6 fatty acids. If you're concerned, choose oils with a higher omega-3 content or oils that have lots of MUFAs - such as olive oil or avocado oil.

Should I cut seed oils from my diet?

There's no need to cut seed oils from your diet entirely. But it's a good idea to limit your intake of ultra-processed foods that are high in seed oils, since they're often high in sugar, salt, and additives as well. These foods are linked to many health issues, including cardiovascular disease and cancer.

If you cut back on ultra-processed foods, many of which are made with corn or soy oil, you will naturally lower your intake of seed oils. Then, you can focus on getting the right daily amount of oil (about 2 tbsp in a 2,000-calorie diet) from nourishing oils that you can use for cooking or for making sauces and salad dressing. That's better than eating lots of ultra-processed food.

What about the smoke point of oils?

Some people may choose an oil based on the culinary use and the oil's smoke point - the temperature that oil can be heated to before it begins to smoke and turn rancid. Cooking oils degrade when they're exposed to heat, which produces byproducts that can have adverse health effects.

Studies show that oils with more MUFA and antioxidants, such as extra virgin olive oil, yield lower levels of harmful compounds compared to oils with more PUFA, such as canola, safflower, and sunflower oil.

When cooking at high temperatures, make sure to choose the right oil for the job.

Here are the smoke points of common oils:

• Avocado oil: 520˚F

• Safflower oil: 450˚F

• Sunflower oil: 450˚F

• Corn oil: 440˚F

• Canola oil: 400˚F

• Grapeseed oil: 400˚F

• Virgin olive oil: 391˚F

• Extra-virgin olive oil: 375˚F

List of seed oil alternatives and oils for cooking

When reviewing the scientific literature on oils, it turns out that it's not a seed oil that comes out on top. Instead, it's olive oil, which is linked with many health benefits. It's especially good to use extra virgin olive oil, which contains polyphenols. Studies show that it can help lower blood sugar and blood pressure. It may even help protect heart health.

Avocado oil (also not made from seeds) is high in MUFA and has a strong reputation as a healthy oil, too. Replacing butter with avocado oil helps improve insulin, total cholesterol, and low-density lipoproteins (LDLs). It can also help with your triglyceride levels and inflammatory markers, such as C-reactive protein (CRP).

If you're choosing a seed oil, pick one that has some omega-3 fats and the most MUFA, such as canola oil. If you're worried about how seed oils are processed, you can buy cold-pressed oils - this means they're made without heat or chemicals. They're pricier than oils that use heat and chemical extraction. But they may have a slight advantage since the heat process can destroy some nutrients. If they're still too pricey, heat-pressed oils are a fine choice.

That said, some nourishing seed oils have a very low smoke point. So you shouldn't use them to cook. They're perfect for salad dressings, cold sauces, or sprinkling on pasta or vegetables. Some great choices of seed oils that are high in omega-3 fats include:

• Flax oil

• Hemp oil

• Chia oil

Frequently asked questions

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