The Major Takeaways:

• Seed oils include oils such as sunflower, canola, and soybean oil, and are often found in ultra-processed foods like fast food, chips, and pastries

• Experts are nearly divided 50/50 on whether they are health promoting or not

• Seeds oils are high in omega-6 fatty acids, which are essential, but in small amounts, so when eaten in excess they can contribute to chronic low grade inflammation

• Research shows that ingestion of seed oils can reduce (or don't affect) your risk of mortality, and chronic diseases like metabolic disease, cardiovascular disease, and cancer

• My Registered Dietitian Nutritionist's opinion: Seed oils are fine when consumed in moderation, but may cause harm when consumed in excess, especially in the absence of adequate intake of omega-3 fatty acids or in patient populations already experiencing high levels of inflammation. In addition, seed oils that have been processed than others are going to be less nutrient dense than oils that have been less processed, such as cold pressed oils. This is because the processing removes many of the beneficial nutrients, such as polyphenols and vitamin E, that are naturally occurring in some oils.

Seed Oils: A Polarizing Subject

I feel like even saying the word "seed oils" is extremely triggering. They are probably the most contentious and hotly debated topic in the health and nutrition space. But where did this schism between "seed oils are toxic" versus "seed oils are healthy" even begin?

If you've interacted with social media platforms like TikTok or Instagram, you'll likely encounter videos of influencers or so-called nutritionists and health experts perusing the aisles of grocery stores. It seems like many of them get a high off pointing out which products contain seed oils and how they are toxic and leading to all of our health issues in this country such as obesity, diabetes, and cardiovascular disease.

But then you also see videos of health professionals pleading to the public to not listen to the fear mongering related to seed oils, and that seed oils are anything but toxic. Many of these healthcare professionals are licensed Registered Dietitians.

Rarely do you see people meeting in the middle. It's either avoid seed oils at all costs or gladly welcome them in your regular diet.

After combing through the actual scientific research and recognizing that nutrition exists on a spectrum (it's never black and white!!), I'm happy to report that there is middle ground when it comes to seed oils.

First, let's learn more about what seed oils actually are!

What Are Seed Oils?

I'm concerned that many people who claim seed oils are toxic for you don't even know what seed oils are. To start, seed oils, often called industrial seed oils, are a type or a subset of vegetable oils that are derived from seeds and are typically high in linoleic acid (omega-6 fatty acids), and therefore, may be considered more pro-inflammatory. We'll get into that concept more further in the article…

Seed oils are vegetable oils in which the oil comes from the seed of a plant, rather than the fruit of a plant. Seed oils include:

• Corn

• Canola

• Cottonseed

• Soy

• Sesame

• Sunflower

• Safflower

• Grapeseed

• Rice bran

• Peanut

On the other hand, vegetable oils are derived from plant matter, whether it's from fruits, grains, seeds, or nuts. In other words, seed oils are considered vegetable oils but not all vegetable oils are seed oils. Some of the more popular vegetable oils include:

• Coconut

• Olive

• Palm

• Avocado

• Macadamia

• Walnut

All of these vegetable oils have different arrays of fatty acid ratios (ratio of omega-3 fatty acids to omega-6 fatty acids), meaning they vary widely in their linoleic acid (omega-6 fatty acid) content.

When Did Seed Oils Enter the Food System?

Fat has always been part of the human diet, but seed oils were only introduced to the food supply in significant quantities about 100 years ago. Crisco was the original processed oil, and soon after oils like soybean, corn, and canola oil were introduced.

Most Americans regularly used animal fat sources, such as beef tallow, lard, and butter. It took a few decades for these plant-based cooking oils to enter American's pantries, but overtime they've become staples throughout our households. There have been a multitude of creative, health-oriented, and sometimes patriotic marketing campaigns to incentivize consumers to purchase these products.

It wasn't until the 1950s when new research unveiled the connection between saturated fat and heart disease that seed oils ultimately replaced the use of butter in many households. The animal-based fats like butter and lard are rich in saturated fat, while plant-based seed oils are mostly comprised of polyunsaturated fats.

However, as science is intended to work, new research has shown that while these seed oils are low in saturated fat, they are also higher in certain types of unstable polyunsaturated fats that may contribute to conditions like heart disease, diabetes, autoimmune disease, and cancer.

Saturated Fat Versus Unsaturated Fat

As a Registered Dietitian, I sat through multiple semesters of chemistry, organic chemistry, and biochemistry so I have a firm understanding of the structural difference between saturated and unsaturated fats. This knowledge has allowed me to better understand why a diet high in saturated fats can lead to heart disease, as opposed to a diet that contains a balance of saturated fats and unsaturated fats.

I won't give you a full-blown chemistry course on the molecular structure of these fats, but I am going to give you the boiled down version so you can also have a general understanding of how these different fats interact in your body.

Structurally, saturated fats are stable and less flexible than unsaturated fats. They are "saturated" with hydrogen atoms, which makes them solid at room temperature, have a higher smoke point, and therefore are considered more stable than unsaturated fats.

Unsaturated fast have one or more double bonds. Double bonds are an area on a fatty acid chain where hydrogens are missing, which creates more flexibility in the fatty acid, but also makes them more susceptible to oxidation or rancidity.

When there is more than one double bond on a fatty acid chain, the unsaturated fat is called polyunsaturated, or PUFA for short. PUFA's are named after the first double bond on the fatty acid chain. For example, if the first double bond is on the third link of the chain, it's considered an omega-3 fatty acid. If the first double bond is on the sixth link on the chain, it's an omega-6 fatty acid.

Seed oils are particularly rich in the omega-6 fatty acid known as linoleic acid. Linoleic acid is an essential fatty acid, but it's a fat that humans didn't eat in high quantities until the last 100 years. The other essential fatty acid, or alpha linolenic acid, is an omega-3 fatty acid. Omega-3 fatty acids are considered anti-inflammatory and cardio-protective. They are found in foods such as avocado, chia seeds, flax seeds, cold-water fatty fish, and olive oil. Many of these food sources also contain beneficial polyphenols, unlike many of the foods rich in omega-6 fatty acids, such as soybean oil.

How Are Seed Oils Made?

A processed food is not inherently bad or dangerous, but there are different types of food processing that are going to be better or worse for your health. For example, rolled oats are indeed a processed food, but they offer us a great source of soluble fiber and carbohydrate. Soda is a processed beverage that offers us calories in the form of sugar, and nothing else aside from a satisfying taste to some people and caffeine.

Comparing rolled oats with soda isn't necessarily a fair comparison, but I'm using this example to demonstrate the wide range of foods that sit under the umbrella of processed foods.

It's also a good comparison for demonstrating how the addition of certain chemicals and preservatives to some processed foods can pose threats to your health over time. For example, aspartame, a zero calorie sweetener that is added to many diet sodas, has been linked to inhibition of brain serotonin and dopamine which poses some threats to your mental health. You can read more about artificial sweeteners and sugar substitutes through my blog post All About Artificial Sugars, Non-nutritive Sweeteners, and Sugar Substitutes.

In order for seed oils to reach your kitchen pantry, manufacturers will need to harvest, clean for impurities, shell off the hulls, crush, rip, and condition the seeds so they can eventually expel or press the oils.

Any oil that you buy off the shelf in a grocery store, goes through the same initial process. However, when you get to the expel or pressing steps, this is where things can change. Oils can either go into pressed raw oil, which is then filtered, or it can go into press cake which is then flaked, and then eventually will go through a chemical process to remove impurities.

An example of chemical processing is using hexane extraction techniques. In this chemical extraction process, a hexane and oil mixture is created, which can then be distilled into a raw oil. The reason why manufacturers are using this chemical based processing technique is because doing this extra extraction leads to higher yields of the seed oil.

If we're being totally honest, many processes in the food supply are meant to maximize yield. Hexane extraction is a perfect example of this.

The bleaching and deodorizing steps of some seed oil production are typically what many critics of seed oils take issue with. It's important to note that pressed raw seed oils exist, which means these oils have not gone through a deodorizing or bleaching step. In fact, there are some vegetable and canola oils that are pressed raw. However, a lot of the oils that would be used for frying food are typically bleached and deodorized to remove the impurities from the oil itself.

So Are Seed Oils Bad For You?

Like anything, I typically avoid using "good" versus "bad" when describing food because it's rarely that black and white. Seed oils do provide us with some benefits when consumed in moderation. Seed oils contain primarily polyunsaturated fatty acids, which have been shown to help lower cholesterol levels.

However, there are some valid and evidence-based reasons why seed oils aren't always the more optimal choice.

They disrupt the omega-6 to omega-3 fatty acid ratio

Omega-6 fatty acids alone aren't the problem. In fact, some studies show they can lower LDL cholesterol (the type of cholesterol that has been linked to cardiovascular disease when elevated), increase HDL cholesterol (the type of cholesterol that is considered cardio-protective), and even boost insulin sensitivity.

However, low grade chronic inflammation has been linked to consuming too many omega-6 fatty acids relative to omega-3 fatty acids. Up until about 100 years ago, the omega-6 to omega-3 ratio has been around 4:1 or less. The typical Western diet now provides an omega-6 to omega-3 ratio of approximately 20:1 in favor of omega-6. This has predisposed us to supra physiologic inflammatory responses, which can perpetuate chronic low-grade inflammation.

Research has shown us the ideal omega-6 to omega-3 ratio is somewhere between 1:1 and 4:1. Overconsumption of processed oils in pre-packaged food, ultra processed foods, and fried foods in the average American diet has moved us further away from this ideal ratio.

As a Registered Dietitian, I'm still going to be skeptical saying that "seed oils are toxic." Most of the research suggests if our diets are balanced with enough of the anti-inflammatory omega-3 fatty acids, your consumption of omega-6 fatty acids is less of a concern.

It's also important to highlight there is no research that states by decreasing or removing your intake of omega-6 fatty acids, you are also decreasing your exposure to inflammation. However, there is research stating that by increasing your intake of omega-3 fatty acids, you are also decreasing your exposure to inflammation. What this evidence suggests is that omega-3 fatty acid intake can produce beneficial effects in the body, but it does not suggest that omega-6 fatty acids outright produce negative impacts in the body.

It goes back to my favorite word as a dietitian… balance!!

They're prone to oxidation

Many seed oils have a high smoke point, which is why they're so attractive in certain food preparation processes, such as frying. When seed oils are heated, the fatty acids may oxidize and form harmful compounds referred to as free radicals. Free radicals are extremely unstable molecules in the body.

When free radicals build up in the cells of our bodies, they can cause damage to other molecules, such as DNA, lipids, and proteins. This damage may increase the risk of cancer and other diseases.

This doesn't mean consuming foods with seed oils in moderation is going to flood your body with free radicals. Luckily, our bodies are amazing and have the ability to stabilize these free radicals when we give them the tools they need. These tools exist as antioxidants such as vitamin C, vitamin A, and vitamin E, which are rich in foods like fruits and veggies.

Dare I say it goes back to balance?

They're not the most nutrient-dense choice

Unlike cold-pressed oils, such as olive, avocado, walnut, or flaxseed oil, seed oils often go through extensive processing which strips them of antioxidants and other beneficial phytonutrients.

They're energy dense

Like other oils, seed oils are essentially pure fat which is a very energy dense macronutrient. Protein and carbs contain about 4 kilocalories per gram, while fat contains about 9 kilocalories per gram. You might not realize you're eating seed oils because they're so pervasive in our food system. They're often in dairy free milks, salad dressings, and chips.

This is a large reason why diets high in ultra processed foods can lead to excess intake of calories, leading to weight gain.

Essentially, ultra processed foods are energy dense and lack other anti-inflammatory nutrients like fiber and antioxidants to balance things out. This is why seed oils have been considered inflammatory.

Should You Avoid Seed Oils?

While consuming foods that contain seed oils every once in awhile is unlikely to trigger chronic and systemic inflammation in your body, it's worth being mindful of your overall eating habits and intake of processed and packaged foods. These types of foods were not part of our regular diet for hundreds of years, so we do not know the long-term effects.

Critics argue we are starting to see some of the long-term effects given the rise in diseases like cardiovascular disease, diabetes, and cancer. However, we cannot prove causation directly from seed oils. This is what makes nutrition research so difficult! It's likely multifactorial.

Following a few simple strategies can help you balanced your intake of seed oils, and therefore help you meet the more optimal ratio of omega-6 fatty acids to omega-3 fatty acids.

• Everything in moderation: using a whole source of seed oil at home, such as safflower or sesame, to stir fry your veggies is okay in moderation, but use monounsaturated oils like avocado and olive oil more often

• Choose more omega-3 fatty acids: incorporate more omega-3 rich foods like salmon, sardines, walnuts, and flax seeds into your diet to improve your ratio of omega-6 to omega-3 fatty acids.

• Limit processed foods: minimizing your intake of ultra-processed foods like fast food, chips, store-bought salad dressing and sauces that contain seed oil will automatically reduce how many seed oils you consume.

• Don't stress too much: it's not worth the added stress to your body dwelling on if the restaurant you're at uses seed oils or if that latte you love from your favorite coffee shop uses almond milk with seed oils in it. Your body is resilient and life is too short to sweat the small stuff!

References:

1. DiNicolantonio JJ, O'Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart. 2018;5(2):e000898. Published 2018 Sep 26. doi:10.1136/openhrt-2018-000898

2. Ramsden CE, Faurot KR, Carrera-Bastos P, Cordain L, De Lorgeril M, Sperling LS. Dietary fat quality and coronary heart disease prevention: a unified theory based on evolutionary, historical, global, and modern perspectives. Curr Treat Options Cardiovasc Med. 2009;11(4):289-301. doi:10.1007/s11936-009-0030-8

3. Scoditti E, Capurso C, Capurso A, Massaro M. Vascular effects of the Mediterranean diet-part II: role of omega-3 fatty acids and olive oil polyphenols. Vascul Pharmacol. 2014;63(3):127-134. doi:10.1016/j.vph.2014.07.001

4. Mojtaba Yousefi, Hedayat Hosseini (2017) Evaluation of Hexane Content in Edible Vegetable Oils Consumed in Iran . Journal of Experimental and Clinical Toxicology - 1(1):27-30. https://doi.org/10.14302/issn.2641-7669.ject-17-1790

5. DiNicolantonio JJ, O'Keefe J. The Importance of Maintaining a Low Omega-6/Omega-3 Ratio for Reducing the Risk of Autoimmune Diseases, Asthma, and Allergies. Mo Med. 2021;118(5):453-459.

6. Mariamenatu AH, Abdu EM. Overconsumption of Omega-6 Polyunsaturated Fatty Acids (PUFAs) versus Deficiency of Omega-3 PUFAs in Modern-Day Diets: The Disturbing Factor for Their "Balanced Antagonistic Metabolic Functions" in the Human Body. J Lipids. 2021;2021:8848161. Published 2021 Mar 17. doi:10.1155/2021/8848161

7. Perumalla Venkata R, Subramanyam R. Evaluation of the deleterious health effects of consumption of repeatedly heated vegetable oil. Toxicol Rep. 2016;3:636-643. Published 2016 Aug 16. doi:10.1016/j.toxrep.2016.08.003