Kendra Pierre-Louis: For Scientific AmericanIt is Science quickly, My name is Kendra Pierre-Louis, I’m replacing Rachel Feltman.
What do ready-made cinnamon rolls, most fries, and many premade salad dressings have in common? They are all made with seed oils.
Until recently, many of us might have worried How much oil these contained foods rather than their type. But these days, many people seem to have a problem with seed oils.
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Everyone from so-called wellness influencers on social media to Robert F. Kennedy Jr., Secretary of Health and Human Services, wants us to believe that seed oils are particularly bad for us. The Health Secretary went so far as to claim, without evidence, that seed oils are toxic. And some restaurants, including salad chain Sweetgreen, are increasingly touting seed oil-free options.
So today we’re looking at seed oils: what are they and are they secretly killing us? To answer these questions, we contacted Eric Decker. He is a professor at the Center for Agriculture, Food and the Environment at the University of Massachusetts Amherst.
Hello, thank you for taking the time to speak with us today.
Eric Decker: No problem. It’s my pleasure.
Pierre-Louis: One of the reasons we wanted to talk to you is because you’re sort of an expert on seed oils, which in recent years have become the villains of social media, you know, quote, “wellness.” For me, this raises a pretty natural question: what is seed oil?
Decker: Basically the fats we eat could come from animals, so that would be things like lard, tallow and butter; or they can come from fruit, and that would be things like olive and avocado; or they can come from seeds, and those seeds can be soybeans, corn, canola or sunflowers.
Pierre-Louis: So something like corn or soybean oil would be a seed oil…
Decker: Correct.
Pierre-Louis: But something like olive oil or, my personal enemy because I’m allergic to it, avocado oil, ie not a seed oil.
Decker: Correct.
Pierre-Louis: But when I look in my kitchen cabinets, I see, for the most part, liquid oils that all look exactly the same. Are seed oils chemically different from non-seed oils?
Decker: Yeah, they’re going to have some differences. What makes olive oil unique is that it is not a refined oil, but extra virgin olive oil…
Pierre-Louis: Mm-hmm.
Decker: Avocado oil, sometimes refined; sometimes it’s not refined. Most of the seed oils we buy at the supermarket would be refined. Cold-pressed seed oils exist, but they are quite rare.
So whether they are refined or not could be one of the reasons why their composition will change. But the other thing is that the genetics of the plant dictate the type of fatty acids in the oil.
Pierre-Louis: Mm-hmm.
Decker: And therefore olive and avocado oil, very rich in oleic acid…
Pierre-Louis: Mm-hmm.
Decker: Which is a monounsaturated fatty acid.
Pierre-Louis: Mm-hmm.
Decker: In seed oils you can find a very wide range of fatty acid compositions. So canola oil would be very rich in monounsaturated…
Pierre-Louis: Mm-hmm.
Decker: Like olive oil and avocado oil. But others, like corn, soy, safflower or sunflower, are rich in polyunsaturated fatty acids, and the most common of them is linoleic acid…
Pierre-Louis: Mm-hmm.
Decker: Which has two double bonds, versus monounsaturated with one double bond.
Pierre-Louis: Okay, so for a regular person who is just trying to figure out what they should be eating on the grocery aisle, are these fatty acids important?
Decker: Yes, so there is some very good human clinical data that shows that polyunsaturated fatty acids lower LDL cholesterol in your blood. And that’s important because LDL cholesterol has been linked to cardiovascular disease and heart attacks…
Pierre-Louis: Mm-hmm.
Decker: So people who, especially people who have high LDL…
Pierre-Louis: Mm-hmm.
Decker: It would be greatly beneficial to use a seed oil with a high concentration of linoleic acid.
Pierre-Louis: Wait, what? Because I have it on good authority from our Secretary of Human Health, Robert F. Kennedy Jr., that Americans are being “unknowingly poisoned” by seed oils. Here’s what he said in an interview on Fox & Friends in 2024.
[CLIP:RFKJrspeaksinanAugust242024interviewon[CLIP:RFKJrspeaksinanAugust242024interviewonFox and Friends Weekend: “Seed oils are one of the unhealthiest ingredients we have in foods…Seed oils are associated with all kinds of very, very serious illnesses, including body-wide inflammation.”]
Decker: Yes, there are a lot of theories about this. There is a theory called the omega-3/omega-6 ratio…
Pierre-Louis: Mm-hmm.
Decker: And this theory – omega-6, which is polyunsaturated linoleic acid, would increase inflammation…
Pierre-Louis: Mm-hmm.
Decker: While omega-3s, most of which come from fish oil…
Pierre-Louis: Mm-hmm.
Decker: Would reduce inflammation. So even though this is just a theory and it’s been demonstrated in animals, when you actually look at the human clinical trials…
Pierre-Louis: Mm-hmm.
Decker: Linoleic acid, omega-6, has not been shown to increase inflammation. So, right now, research shows that the benefit of linoleic acid in lowering your LDL cholesterol is far greater than the potential risk of this fatty acid increasing inflammation.
I mean the other controversy about seed oil is that they are extracted with hexane…
Pierre-Louis: Mm-hmm.
Decker: Which is a chemical solvent. But there is some pretty good data that shows that for the consumer, it doesn’t really pose a high risk. Almost all hexane is removed from oil during its processing. And really, the only time you see hexane being a problem is with factory workers who are exposed…
Pierre-Louis: Yeah.
Decker: At very high levels of hexane.
Pierre-Louis: From the outside, it often seems to me that when I go to the grocery store and look at these seed oils, they are often less expensive than some of the other oils that we are pushed to consume instead. And I wonder: I feel like there’s a bit of classism at play here and this idea that just because it’s expensive, it must be better for us.
Decker: The best example is therefore extra virgin olive oil. They just extract the fat, and when they extract the fat, they don’t remove all the fat from the olive…
Pierre-Louis: Mm-hmm.
Decker: The yield is therefore somewhat low. Additionally, olives can only be grown in warm climates, so there are…
Pierre-Louis: Mm-hmm.
Decker: Limiting Amounts Spent: There are actually shortages occurring right now due to climate change. They will therefore generally be more expensive. And when you think about olive oil, it really has a lot of flavor, and that flavor is very sought after in olive oil. And that’s why you don’t want to refine it, because that takes all the flavor out of it.
Seed oils, for their part, are extracted with hexane…
Pierre-Louis: Mm-hmm.
Decker: And when they are extracted with hexane, it becomes all the oil comes out, so it’s very, very effective. But it removes other fats, like phospholipids, free fatty acids, and fats that are undesirable in the oil. So the refining process removes these other lipid components from the oil, which gives the oil a very bland flavor; this gives it very good cooking properties, such as a very high smoke point; and so that makes these oils very, very versatile. But since they are very efficient at extracting it, it also reduces costs.
Pierre-Louis: And isn’t that also why people like to fry in peanut oil, because it has a high smoke point?
Decker: Yeah, they’re all pretty similar; all refined oils are quite similar. If you eat a lot of saturated fats, they will be a little higher…
Pierre-Louis: RIGHT.
Decker: But, you know, peanut oil is a good oil, because in a lot of these applications, when you’re cooking, you want bland, right? You don’t want to make your sugar cookies with olive oil.
Pierre-Louis: [Laughs.]
Decker: [Laughs.] So you want, you know, you want a bland – or maybe in the case of a cookie, you want butter, right? But in some applications…
Pierre-Louis: Mm-hmm.
Decker: You don’t do it I want the oil to have flavor.
One thing about olive oil is that it’s actually not good to cook olive oil at high temperatures because its smoke point is low and you’ll lose a lot of the flavor you’re paying for. So you should use it in cold applications or in… you know, you can use it in a frying pan, which doesn’t get too hot.
I think there is a risk in all oils…
Pierre-Louis: Mm-hmm.
Decker: If you heat them too high and they start to smoke, you are now breaking down the oil into other compounds that pose health risks. So it’s also very important to manage your oil well when cooking with it and not let it get too high a temperature and start to smoke.
Pierre-Louis: It’s true, and this is where it helps to know how to cook a little and look for the smoke point. But I guess there’s a health halo around the more expensive oils and we vilify the cheaper, more accessible oils.
Decker: Yes, I mean, extra virgin olive oil has this halo, and there’s a lot of interesting research showing that it has health benefits beyond normal oils. A very good contrast is your favorite avocado oil.
Pierre-Louis: [Laughs.] Which, to be clear, I diff soul only because he wants me dead, therefore. [Laughs.]
Decker: [Laughs.] So avocado oil doesn’t really have any data showing that it has any major health benefits, and in fact its fatty acid composition, in terms of the amount of monounsaturated fatty acids, is very similar to that of canola oil. So, and when you go to the store and you look at olive oil or avocado oil, you see that a lot of times it’s refined; it’s not cold pressed. And so if it’s refined, then you’re removing other potentially beneficial compounds from the oil, and it’s even more like canola oil, except it’s probably four times more expensive.
So it’s more that people are turning these cold-pressed oils into superfoods when there’s really no evidence to show, especially with avocado oil, that that’s true.
Pierre-Louis: That’s, A, great to know, and, B, I hope the word spreads Because people put avocado oil in everything for no reason [Laughs] as an allergic person.
But what I’ve noticed is that the people who really hate seed oils don’t just promote other vegetable oils, like olive or palm oils. They really push us to use animal fats, like butter or rendered beef, in other words tallow.
You’ve probably heard that fast food chain Steak ‘n Shake, for example, announced that it would eliminate seed oils in favor of beef tallow. And actually, if you go to the website, they sell jars of beef tallow. And that makes me think that Steak ‘n Shake is just fundamentally transformed fast food. And I can’t imagine that even if you were to replace the oil that they were using before with a, quote, “healthier” oil, that it would make such a big difference in the health of ordinary people.
Decker: Yes, there are two sides to this controversy. The first is that some people don’t think that saturated fats are that bad for your health, but again, there is very good clinical evidence that saturated fats raise your LDL cholesterol levels. They do the opposite of polyunsaturated fats. So, especially if you were to replace polyunsaturated fats with saturated fats, you would be diminishing the benefits of healthy polyunsaturated fats in your diet.
However, on the other hand, there is oxidation that occurs in oils, and when these oils oxidize, they begin to break down into a whole variety of compounds, some of which, in animal studies, have been shown to have some toxicity. So if you’re doing something, say in food service, and you’re frying foods with these highly polyunsaturated fatty acids, they can oxidize and produce these products, whereas if you use something like tallow, which is saturated, it’s much more stable against oxidation and doesn’t, again, have that risk.
Now, as long as you take care of the oil you use in the fryer, there is no real risk. The risk becomes — is when the oil is not used correctly.
Pierre-Louis: And what does “used correctly” mean?
Decker: This simply means that you need to make sure to keep the oil in the freshest condition possible. Good catering operations will filter and clean their oil regularly. And then you have to monitor the oil, and when it gets old, you have to throw it away and start again with fresh oil.
Pierre-Louis: In a way, you’re saying that using beef tallow gives fast food restaurants an easier margin, so they can, essentially, use an older oil than they would if they were using a seed oil.
Decker: Yeah, tallow would last a lot longer. And it costs a lot of money to fill that fryer with oil, as you can imagine, so the longer you can make your oil last, the more money you’ll save.
Now another part of beef tallow is that beef tallow can have very positive flavors.
Pierre-Louis: Mm-hmm.
Decker: So for many years McDonald’s used beef tallow. And then what happened was people were concerned about the cholesterol levels in beef tallow, so McDonald’s stopped using beef tallow. But often, if you go to fancy restaurants, you can enjoy fries cooked in beef tallow or even duck fat…
Pierre-Louis: Yeah.
Decker: Sometimes you see duck fat fries. And that’s part of the benefit is you get a flavor in addition to the stability of the fat.
Pierre-Louis: And it also seems that for your daily life, you’re not looking for flavor, maybe you’re making a stir-fry, a seed oil is fine. If you really want a strong flavor, maybe you’re making a pasta dish or a salad, this is a really good place to use your extra virgin olive oil because it adds a really nice flavor profile.
Decker: Exactly.
Pierre-Louis: And to be clear, I love a good duck fat fries; they are very tasty. But I’m also not convinced that a potato fried in duck fat is good for the heart. [Laughs.] I am not making any health claims. And I think the thing about seed oils in particular is that a lot of people vilify them is that they make an explicit health claim and tell people to have diets that are very high in saturated fats and to really move away from eating, you know, canola oil or oils that are, for many people, less expensive, more accessible and – this seems to be, based on the available evidence – better for our health.
Decker: Yeah, I mean, I would say that the influencers who have had so many negative comments about seed oil aren’t really based on solid scientific evidence.
And you know, like you said, the recommendation really should be, “Eat less fried foods,” right, because fried foods are generally very high in calories. If it’s potatoes or chicken nuggets, they won’t be very high in positive nutrients.
So the message is… seems to be completely messed up. We should not worry about the question: “Is seed oil better than tallow?” » We should be concerned about people who consume so much fried foods in their diet.
Pierre-Louis: This is our show. Join us Friday, when we explore Venezuela’s oil reserves and why the United States seems to want them.
Science quickly is produced by me, Kendra Pierre-Louis, with Fonda Mwangi, Sushmita Pathak and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck check in on our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more recent and in-depth scientific news.
For Scientific American, This is Kendra Pierre-Louis. See you next time!