Influencers are sounding the alarm about the many alleged dangers of seed oils. Let’s look at the evidence.
Influencers are sounding the alarm about the many alleged dangers of seed oils. Let’s look at the evidence.
Related listening:
Does the Ratio of Omega-6 Fats Really Matter? (Nutrition Diva #185)
Hello, I’m Monica Reinagel and you are listening to the Nutrition Diva podcast, a show where we take a closer look at nutrition research, trends, and headlines so that you can make better decisions about what you eat.
Lisa recently emailed me to ask about seed oils. “I see seed oils being demonized on social media. Is this just the latest food fear, or does evidence back it up?”
Nutrition influencers (which doesn't necessarily mean nutrition experts) have raised a variety of concerns about certain types of vegetable oils. Ironically, these oils are often recommended as heart-healthy choices. Let’s take a look at the various charges and see what the research says.
First, what do we mean by seed oils? Although this term may sound a bit unfamiliar, you have almost certainly been consuming seed oils your entire life. Soybean, corn, canola, sunflower, and safflower oil are akk considered seed oils. The ambiguously named “vegetable oil” is usually made primarily from soybeans, sometimes blended with other seed oils or other plant-based oils such as peanut or olive oil. Originally, the term served to distinguish plant-based oils from animal-based ones like lard.
Food manufacturers love seed oils because they tend to be neutral in flavor, relatively inexpensive, and shelf stable. That’s why seed oils so frequently turn up in processed and packaged foods such as chips, crackers, cookies, pastries, salad dressings and mayonnaise.
Most seed oils are high in polyunsaturated fatty acids (PUFAs) and low in saturated fatty acids, which is how they got their reputation for being heart healthy. Specifically, research suggests that replacing saturated fats with unsaturated fats can lower cholesterol levels and reduce risks related to heart disease. However, for some, that high PUFA content is also a source of concern.
The PUFAs in most seed oils belong to the omega-6 family of fatty acids. Omega-6 is an essential fatty acid, crucial for various bodily functions. It also plays a role in the body’s inflammatory response. Ideally, the effects of omega-6 are balanced by the anti-inflammatory effects of omega-3 fatty acids. However, with its heavy reliance vegetable oils and processed foods made with them, the modern diet tends to provide a disproportionately high amount of omega-6 compared to omega-3. This imbalance is thought to contribute to inflammation and has been associated with various health issues.
For more on this, please see Episode #185: Does the ratio of Omega-6 fats really matter
Now, there are two seed oils which are notable exceptions. Flaxseed, of course, is especially rich in omega-3 fat. However, flaxseed isn’t used very frequently for cooking. Canola oil, on the other hand, is a very commonly used cooking oil. However, unlike most seed oils, canola is rich in monounsaturated fats (or, MUFAs), which are generally considered to be anti-inflammatory. Canola also contains some PUFAs, but with a more favorable balance of omega-6 to omega-3. But some of the other concerns about seed oils still apply to canola.
One concern is the chemicals that are sometimes used to extract oils from seeds, especially a compound called hexane. Hexane vastly increases the efficiency of oil extraction from seeds. However, detractors point out that it is a highly toxic substance.
It's absolutely true that hexane is a neurotoxin. You would be well advised to avoid drinking or bathing in it. This is why its use industrial settings is strictly regulated, in order to protect workers and the environment from harmful exposure.
Another feature of hexane is that it is extremely volatile. A volatile chemical doesn't stick around for long; it quickly dissipates into the air. This means that very little hexane will be present in the oil once it's processed. And, in fact, this is also strictly regulated, to ensure that consumers are not exposed to harmful amounts of hexane.
It is possible to produce canola and other seed oils without hexane, using less efficient mechanical extraction methods (for example, squishing). There is also growing interest in new greener extraction methods, such as aqueous-assisted enzyme extraction. So if hexane is a concern, it is possible to avoid it. However, even if its produced without hexane, some still object that seed oils are simply too processed.
After they are extracted, seed oils are typically refined. This extra step may make them more processed but it also provides some benefits. Refining oils removes impurities which makes them more shelf-stable. Refining also generally raises the smoke point of the oil, making it better for high heat cooking. In fact, contrary to popular belief, the smoke point of an oil has more to do with its level of refinement than what kind of oil it is. However, smoke point is not the only consideration when heating up oils.
Oils that are high in PUFAS, (such as most seed oils), tend to form a harmful compound called HNE when they’re heated. This happens even in oils that are highly refined and have a high smoke point. HNE ends up in the food that are cooked in the oil and is taken up in the body, where it can have damaging effects.
The longer or more frequently you heat up oil, the more HNE it will contain, which is why it’s really not a good idea to reuse cooking or frying oil. Of course, most restaurants not only fry foods in polyunsaturated oils, but reuse the oil over and over again. Consider that one more reason to limit your consumption of fried foods.
One last concern I want to address is that oil from canola, soy, corn, and cottonseed is likely to be sourced from genetically modified seeds, or GMOs. In fact, unless the package specifically states that it is GMO-free, you can assume that it is not.
I don’t think I’m going to change anyone’s mind on this. But, for what it’s worth, I do not believe that GMO foods pose any danger or risk–a view that aligns with the vast majority of the scientific and regulatory community. For better or worse, GMO crops have been widely consumed for decades, and over 20 years of monitoring and scientific studies have failed to detect any negative impact on human health. Personally, I’m OK with GMO. If you’re not, you can seek out that GMO-free label.
So, with all of that, here are my recommendations:
Although some of the concerns relating to seed oils may be overblown, I still think oils rich in monounsaturated fats are your best bet as your primary oil. For me that’s generally olive oil, although avocado and canola are also good choices. These oils are heart healthy, safer when heated, and there’s no worry about over-doing the omega-6.
I keep a few other special oils on hand, as well, such as walnut oil (which is not a seed oil) and toasted sesame (which is), because both of these come up in recipes from time to time. If you don’t go through these types of oil very quickly, it’s best to store them in the fridge. But I try to avoid using oils that are high in PUFAs, including corn, sunflower, and soybean oil, at high temperatures. But, as I suggested before, It’s probably best to enjoy fried foods in limited quantities, no matter what they are fried in.
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