ZOE Science & Nutrition - Seed oils are not ‘evil’ - they could lower your risk of disease | Prof. Sarah Berry

Episode Date: September 12, 2024

The internet is panicking that seed oils cause inflammation and disease. Yet, they're everywhere. Canola, sunflower, safflower oil - these are all seed oils. So why is there so much fear? And are any of the accusations true? In this episode, we unpack the science of seed oils. With Professor Sarah Berry's expertise, we simplify what seed oils are, what the latest science says and why countless videos online say they’re toxic.  Sarah Berry is a professor in the Department of Nutritional Sciences at King's College London and Chief Scientist at ZOE. She reveals the surprising truth about seed oils and tips to navigate a world full of them. 🥑 Make smarter food choices. Become a member at zoe.com for 10% off with code PODCAST 🌱 Try our new plant based wholefood supplement - Daily30+ *Naturally high in copper which contributes to normal energy yielding metabolism and the normal function of the immune system Follow ZOE on Instagram. Timecodes 00:00 Seed oils are in everything 02:07 Quickfire questions 03:29 What is seed oil? 05:31 Are seed oils full of chemicals? 10:41 Why are seed oils everywhere? 12:46 3 types of fat you should understand 19:32 Are seed oils toxic? 24:03 Is omega 6 dangerous? 26:57 These fats reduce disease risk 29:24 Key seed oil science  37:15 Are seed oils unnatural? 44:57 Seed oil vs palm oil 49:50 Is it safe to cook with seed oil? Books by our ZOE Scientists Every Body Should Know This by Dr Federica Amati Food For Life by Prof. Tim Spector  Fibre Fuelled by Dr Will Bulsiewicz Free resources from ZOE: Live Healthier: Top 10 Tips From ZOE Science & Nutrition  Gut Guide - for a healthier microbiome in weeks MenoScale Calculator - learn about your symptoms Have feedback or a topic you'd like us to cover? Let us know here. Episode transcripts are available here.

Welcome to ZOE Science and Nutrition, where world-leading scientists explain how their research can improve your health. Seed oils are in everything. You'll recognise them as sunflower oil, soybean or canola. That's rapeseed in the UK. They're in our snacks, our restaurants and our pantries. They're inexpensive, they have a neutral taste and a high smoke point, which makes them great for frying. But many people think seed oils are evil. There are countless videos calling them toxic, which have gone viral online. Critics suggest that high levels of omega-6 fatty acids found in seed oils cause inflammation.

And this inflammation can cause a wide variety of conditions, from diabetes to depression, from heart attacks to cancer. If seed oils do boost inflammation, it's a legitimate worry. But is any of this true? Let's pause for a second and ask, as we often do on this show, what does the science say? In today's episode, Dr. Sarah Berry reveals the surprising truth about seed oils and tips to navigate a world that is full of them. Sarah is a world leader in large-scale

human nutritional studies, associate professor in nutrition at King's College London and chief scientist at Zoe. One of her areas of research focuses on the impact of different dietary fats and oils on risk factors for cardiovascular diseases. Sarah, thanks for joining me today. Pleasure. I'm so excited. There is so much neutral nonsense over this topic out there. And so I'm excited to debunk all the myths, Jonathan, and educate you on them as well. Well, I'm very excited about it as well. In a way, this feels a little bit like the conversations that we sometimes have inside Zoe, like with the science team around a particular topic. And so I think it's really fun to do it today and to have like a full length episode

to talk about it as well. Okay. I get a whole hour to talk about oils, which I spent many years researching. Let's start with a quick fire round of questions as always. You know the rules. Yes or no, or one sentence answer if you have to. I know that this gets ever more difficult as it becomes more and more your area of expertise. You willing to give it a go? I am. All right.

Are all seed oils bad for your health? No. Are most vegetable oils a type of seed oil? Yes. Are seed oils in many ultra-processed foods? Yes. Should we be worried about omega-6 fatty acids in our food? No. I was brought up that all oil is basically unhealthy. Is that true? No. All right. Let me ask you a final question. You have a whole sentence, Sarah. What's the most surprising thing that you've learned about seed oils? The most surprising thing I've learned about seed oils is how much nutra-nonsense there is out there about seed oils. It's shocking. We had so many questions from our listeners on this topic. I have to say, this is one of the

largest number of questions we've had on any topic. And we talk about many topics that seem like they would be much more mainstream. So there are a lot of questions around seed oils. And I would say actually many of those questions actually boiled down to something quite simple, which is, should I be scared about seed oil? Should I be trying to avoid them? Can we just start at the beginning though? What is a seed oil and how is that different from some other sort of oil? So we get many different sources of dietary fat in our diet.

So you have animal fats and oils that come from animal products. Dairy is a great example, dairy fat. You have other vegetable oils. So for example, you have olive oil, but the largest source of oil in our diet comes from seed oils. And these are very simply put oil that's extracted from a seed, whether it's sunflower or safflower or corn, the seeds of these plants can be crushed and the oil can be extracted. That sounds pretty straightforward. And you're saying that actually most of the oils that I would find in the grocery store have been extracted from these seeds? Yeah. So the largest contributor of fat in our diet comes from palm oil. Now that isn't a seed oil, but then nearly all of the rest of the oils that we consume come from these seed oils. So one of the most common is soybean

oil, which is very, very common in the US and constitutes the majority of the oil that's consumed there. In the UK, the most common oil is rapeseed oil. That's actually called canola oil in the US and in North America. It's the same thing, just with different labels across different countries. It's exactly the same thing, but just with different labels. And then we, in both countries and in many countries, we also have a high amount of sunflower oil, but to a lesser extent than soybean and rapeseed oil. And then we have minor amounts in our diet of some of these other seed oils like sesame seed oil, corn seed oil, and so forth. And Sarah, how are they actually made?

And part of the reason I'm asking that is like one of the things that's been eye-opening for me over the last couple of years is that some of the things that like I buy turn out to go through like this extraordinary industrial process. And those are things that we've tended to turn out to be calling ultra-processed foods and other things are incredibly straightforward. What's the situation with these seed oils? So it is actually, I think, relatively straightforward. And I think this, again, is one of the arguments that some of the people that claim seed oils to be toxic use that, oh, it's really refined. It's got all of these terrible chemicals in it. And there are different types of ways that you can process oils. And I think it's important

we briefly cover these. So all oil has to firstly be extracted from the seed. Okay. And you can do this a couple of different ways. One way you can do it is what you call cold pressed seed oil. This is literally just in simple terms, squeezing the seeds so that the oil comes out. Now that's all very well, but actually it's not the most efficient process because what happens is lots of the oil gets kept inside the seed. And obviously we always want to maximize production, don't we? Particularly in the food industry, seed and oil industry. So what you can do is you can either heat that seed, or in addition to that, you can add in a particular solvent. And typically, we use hexane as a solvent. And basically, that allows us to extract all of the oil. So it becomes

a more efficient way of extracting the oil. At that point, it can no longer be called cold pressed. And it started to go through what many people would say is a more refined process what can also happen and most of the oils that are used additive foods and most of the oils that you buy off the shelf unless they say they're cold pressed go through further stages of processing and this is to remove many minor components that you might find in the oil and these terms that you might hear that are used as a processing technique techniques are things like bleaching and deodorization now they do sound quite scary people are thinking probably bleaching peroxide it's not as scary as it sounds what happens is is the end oil is therefore very stable there are no harmful chemicals left in that end stage oil

the only potential downside of this is that in that process of where the oil might have been heated or had these additional chemicals added occasionally you might remove some of the other favorable elements and seed oils so seed oils are great not just some of the other favorable elements in seed oils. So seed oils are great not just because of the fatty acid composition, which I know we'll come on to talk about, but because they also have lots of what we call phytonutrients and micronutrients. So they tend to be very high in vitamin E, which is a natural antioxidant. They also tend to be high in other phytonutrients like phytosterols, for example. And what we know is that as you go through the refinement process, some of these can be removed and some polyphenols as well.

These phytonutrients are typically quite well preserved, but you might get some losses. And again, this is one of the arguments that's often used for why you should buy cold pressed rather than refined. What you're saying, I think, is that the end product of this, you're saying is actually still sort of the oil itself rather than a whole bunch of added chemicals that aren't there otherwise. And the downside is actually that you're losing some of these phytonutrients, polyphenols you're mentioning that you would keep with a cold press. So it's losing some of these phytonutrients polyphenols you're mentioning that you would keep with a cold press so it's it's losing some of those benefits but it's not like this ultra processed

food which is full of things that we've never normally digested absolutely and i know this for many people will be considered a controversial statement to make but i actually believe based on current evidence and based on the kind of techniques the seed and oil industry use, that these refined oils actually are very similar to the cold pressed oils. And the loss that you get is quite minor. But I think it's important to say, yes, there is a little bit of loss, but I don't think it's enough to constitute for people who may be finding cold pressed oils very expensive because they are a lot more costly to say, okay, they are really, really this much healthier. Got it. So you're saying there is this industrial extraction process, but your research and the research of other people is suggesting that the end product actually basically looks like

the sunflower oil, the canola oil that you would have got if you just squeezed the seed in the first place. Yeah. And interestingly, there's been a couple of randomized controlled trials that have actually compared cold press versus the refined oil. And they actually don't show any difference in many of the different outcomes that we would think might be impacted by the loss of some of these phytochemicals like inflammation, like oxidative stress. There hasn't been many. And as I know, I always like to caveat, Jonathan, I'm making a statement based on the current evidence. And in five years, 10 years, as I always tell my students, there might be more evidence to say otherwise. But based on current evidence, I don't think there's any harm from the processing techniques that are

used to create processed seed oils. I'd like to share something exciting. Back in March 2022, we started this podcast to uncover how the latest research can help us live longer and healthier lives. We've spoken to leading scientists around the world doing amazing research. And across hundreds of hours of conversations, they've revealed key insights that can help you to improve your health. If you don't have hundreds of hours to spare, no need to worry. At the request of many of you, our team has created a guide that contains 10 of the most impactful discoveries from the podcast that you can apply to your life.

And you can get it for free. Simply go to zoe.com slash free guide or click the link in the show notes and do let me know what you think of it. Okay, back to the show. Is it just cost that is the difference between these different seed oils? Are they the same in terms of what happens when we eat them? What are the main seed oils that people are probably eating both directly, but then also, I guess, added to our food, which I think is often where we eat a lot more of these things than I'd ever realized before. Yeah. So our consumption of a seed oil is changing year on year. And if we look 50 years ago,

how much seed oil we now eat has changed probably two, three hundred fold. So we are eating a lot of seed oils now in our diet. Most of them are actually eaten as part of the food that we're buying. So typically many ultra processed foods, but also many other manufactured foods. We also have them, as you know, in nearly every larder, every food cupboard, we have a vegetable oil or a sunflower oil, or in the case of the US, a soybean oil. In the US, soybean oil is the most popular oil both to cook with at home, but also to be incorporated into foods. And it accounts for probably about 60% of the seed oil that's consumed in the US. Conversely, in the UK, it's rapeseed, which is the most common oil. Again, it's used in equivalent levels probably to soybean oil. So about 60 to 70% of the oil that we eat comes

from rapeseed oil. You said that's canola oil? That's canola oil in the US. So they're the biggest part of the oils. And one of the reasons is because of the composition of these oils. So all of the oils differ. The main reason they differ is because of the composition of these oils. So all of the oils differ. The main reason they differ is because of the fatty acid composition, so the type of fat that's in them. So both soybean oil and rapeseed canola oil have a high level of monounsaturated fatty acids, as well as polyunsaturated fatty acids. Now, sunflower oil has a particularly high level of polyunsaturated fatty acids. Now, Sarah, we've discussed this often. Yeah. And every time we discuss it for like 10 whole minutes, I've got it in my head,

it all makes sense. And then 11 minutes later, it's like, I've lost it all between the monounsaturated and polyunsaturated and what's the fat again, all the rest of it. Could you just like explain to us, you know, why are you even telling us about mono and poly and why does that matter? Yeah. So all the fat that we eat, so all of our dietary fat is made up of different fatty acids. These are like the building blocks of fat. And we categorize these into three main groups based on how we know they impact our health. So the first group is saturated fats. And these, very simply put, are fatty acids that have no double bonds. So that's why we say they're fully saturated with hydrogens. We then have monounsaturated fatty acids. And these are fatty acids that have one double bond. Okay, so they're monounsaturated,

mono meaning one and unsaturation meaning one unsaturated double bond. Then we have polyunsaturated fatty acids, which are fatty acids that have two or more double bonds, hence poly for many and unsaturated, how many double bonds ones they are what we know is that in general saturated fatty acids are bad for our health but this isn't for all saturated fatty acids and that's the topic of a whole other podcast we know that monounsaturated fatty acids are good for our health and we know that polyunsaturated fatty acids are also good for our health however the reason that different oils can be used for different functions based on this mono and polyunsaturated fatty acid content is due to how it affects the stability of the oil.

I think I might have got that, Sarah. Let me see if I've understood it. So first thing you said is like the oils themselves or any fat is made up of these different fatty acids and that's sort of like the building blocks. And so I'm thinking we've had a number of these podcasts talking about protein recently, where they've talked about like proteins being built up of amino acids is this a similar idea here for the for the fats exactly overall fat is made up of these um these building blocks of fatty acids underneath absolutely i'm well done well no no i'm like okay maybe now the seventh time it's starting to make sense and then you said there's three like broad categories of these fatty acids where you go from saturated

at one end, which in general is the least healthy. And I think I've heard of this. Many people have heard of this because we associate it with red meat and butter and milk and things like this. Is that right? Correct. And then you said there's monounsaturated and polyunsaturated, which have a double bond or two double bonds. I still have

no idea what that means, but that's the difference between them. Both of them are generally healthier. And then you say the polyunsaturated is generally even more healthy than the monounsaturated? Yes, correct. Okay. But then you said it's in fact more complicated, which I know from other conversations, because the exact food it is matters. There are some saturated fats that I know you actually think are really not that bad for you, which we've talked about length. Got it. So now we've got those three categories of fatty acids. Back to the seed oils. Do they all have the same mix?

No. So every seed oil differs in the amount of saturated mono and polyunsaturated fatty acids. And it's those mixtures of fatty acids that will determine the health effects of those seed oils together with these other, what I call these phytonutrients that I mentioned earlier. So for example, like the polyphenols in them or the micronutrients, like how much vitamin E might be in them. Because we often, and Tim talks, Tim Spector, my co-founder at Zoe, talks about polyphenols a lot. Is that the same as phytonutrients? Yes, yes, yes. Okay.

So phytonutrients is a broad term that can capture what we also term these non-nutritive bioactives. So these compounds like polyphenols, like phytosterols that are found in foods, also found in oils that have health effects, but aren't what you would typically think of when you think of nutrients, i.e. is it a vitamin? Is it a mineral? Is it a fiber, fat or protein? So it's all these minor compounds. This is part of realizing that the food has like 100,000 chemicals that can all help us or not rather than just 25.

So seed oils differ in terms of the fatty acids. So whether they're saturated monopoly unsaturated fatty acids, and also all of these other chemicals that we know have might have health promoting effects. And this is a bit like the extra virgin olive oil, which is not a seed oil, it's really good for you because it has all of these polyphenols, which you don't see on the label at all. But that's the bit that like you really want. And that's why you want to have it cold pressed, not heated because you lose some of those exactly so extra virgin olive oil the reason it's so healthy for us is partly because of the fatty acid composition it's high in monounsaturated fatty acids which we know are good for us but actually even more so because it has really high

levels of polyphenols which we know these kind of bioactives that have wonderful properties throughout our body. Seed oils in a similar way to olive oil have high levels of mono and polyunsaturated fatty acids. And they also have some of these compounds, but not as many as olive oil. But where the main differences with seed oils actually come to play is the relative proportions of mono and polyunsaturated fatty acids. And that determines also, as well as their health effects, how we might want to use them in foods. So rapeseed and canola oil, as well as soybean oil have quite a high level of monounsaturated fatty acids. And while they do contain polyunsaturated fatty acids, they actually have less polyunsaturated fatty acids than sunflower oil.

So they're more stable to use in cooking. A word that people might be quite familiar with is the smoke point of the oil. So that's the point at which the oil smokes. So you could use a simple word, kind of burning, although that's quite a simplistic way to think about it. And so you will have a higher smoke point for these oils that are richer in monounsaturated fatty acids than you will in oils like sunflower oil that are richer in polyunsaturated fatty acids, which means they're a little bit more stable to cook with. And so that means that soybean or canola, you know, rapeseed, when you're cooking with them,

like the pan has to get a lot hotter before you see it smoking versus something like a sunflower oil. Yes. So rapeseed is particularly high in monounsaturated fatty acids. Soybean has a little bit less monounsaturated fatty acids, and it's a little bit more comparable to sunflower oil, but sunflower oil is the one that has even more polyunsaturated fatty acids. So why are 99% of YouTube videos saying that these seed oils are bad for us? What are people worried about? Because in my experience, often there's some reason, you know, it comes from somewhere. What are they worrying about? Gosh, if only I could get on my soapbox now jonathan uh honestly it's it drives

me insane when i see this and in preparation for this i did google on on i went on to the podcast app and i had a look at cedars and these alarms like cedars are toxic cedars are going to kill you it's absolute nonsense um and so i'm glad i've got an opportunity to set the record straight there's a number of different arguments they use. There's three key arguments that people use as a rationale for saying seed oils are toxic. And I'd love to work through each of these because I think it's important for listeners to be able to understand why this information is misinformation that they're reading. And so very briefly, one of them is that they use as an example, an association of this increase in seed oil with increase in all of these different

health issues that we're having now. And we can dive into this after. The other reason they use is that it creates an unfavorable omega-6 to omega-3 ratio causing inflammation. And again, we can do a deeper dive into this. The third argument they use is, oh, it's unnatural. It's gone through all this refinement process. It's bleached. My God, it's going to kill us because of this process. And then the fourth is that it's prone to oxidation, i.e. these C-dols when they're heated are prone to oxidation. And so what perhaps we could do is work through each of those and debunk each of those four myths. Let's do it, Sarah. I like to see you get so excited. So you've been studying this for what, 25 years? You've been interested

in sort of how fats interact with our body and our health. Is that right? Yeah, 25 years. You're spot on actually. A lot of my trials are looking at all types of fats and not just seed oils, but I have done some work, for example, looking at cooking with seed oils and we can come on to that. Can we start at the beginning? You said, I think you were starting with this suggestion that basically people are, what you said before, that overall we're all eating vastly more seed oil than we were in the past. And we know that we are seeing an explosion of health issues, right? Whether that's living with obesity or diabetes or just this whole host, right, of health issues. Yeah. So one of the first things that people claiming seed oils to be toxic

use is beautiful infographics, beautiful figures that show a nice chart where you see on one axis of this figure, increase in seed oil intake. And on the other axis, you see increase in cardiovascular disease, cancer, type 2 diabetes. Think of all of these chronic related diseases that are increasing over the last 50 years. And you see this almost linear relationship as we call it. So as your intake of seed oil increases, so does the level of all of these different diseases over the years. So that sounds pretty bad. Yes, it does. But that's association. It doesn't mean causationation and what is really alarming here is that it's ignoring everything else that's happening over the last 50 years the fact that actually these seed oils are

typically now eaten as part of these very heavily processed unhealthy foods so actually the majority of our intake of seed oils comes from these cereal basedbased foods, so pastries from cakes and these kind of foods. And so it's not the seed oils themselves that are causing this, it's the ingredients that all of the other ingredients in these foods, but also what else has been happening over the last 50 years. So, you know, our increase in being sedentary, so not, you know, lack of physical activity, our increase in stress, our increase in sleep problems, you know, et physical activity our increase in stress our increase in sleep problems you know etc etc etc all of these other issues so just because in the same time frame that seed oils are increasing these other diseases are increasing doesn't mean one causes the other and so i know that often in science the way that nutritional scientists try to unpick this is this thing

called epidemiology right where you study you study tens of thousands or hundreds of thousands of people over decades, and you look at what they've recorded they've eaten, and you see the difference. And I know that we've seen that for many foods, there is a really strong link between eating more of those foods and worse health outcomes, because you and others talk to me about this all the time. You don't see that link with the seed oils? So if you adjust for all of these other confounders that I've just mentioned, no, you don't. What you see is consistently, there is a favorable effect from increasing omega-6, which is a good marker of seed oil intake with a reduction in coronary heart disease. We know that omega-6, which is this polyunsaturated fatty acid,

so one of the main fatty acids in these seed oils, we know that it reduces our bad cholesterol. It has a very potent effect in reducing our bad cholesterol, which we call our LDL cholesterol. You're saying that what the science is showing is that if you have more of this omega-6 inside you, which you said is one of the monounsaturs? So omega-6 is one of the polyunsaturated fatty acids. There's two types of polyunsaturated fatty acids that we eat. One is called omega-6 and one is called omega-3. And omega-6 is found in particularly high amounts in most seed oils, particularly sunflower oil, like I said earlier. And it is also found in quite high amounts in these other oils like soybean and canola oil. So it's the

main polyunsaturated fatty acid that's in these oils. What we see is that an increase in omega-6 intake from these population epidemiological studies is actually associated with favorable effects on all-cause mortality. So I know you liked, we referred to that as, you know, how likely is people are going to die? It's associated with huge reductions in LDL cholesterol or bad cholesterol, and it's associated with reductions in cardiovascular disease. And it's this omega-6 level that's often used as an argument to why CEDAR was a bad and why you get this association. There's a study that's often referred to as well. It's called the Sydney Heart Study. And this is a key study that people use as a way of saying actually, even in a randomized control

trial, that seed oils are bad for us. And this is a study that was conducted quite some time ago, back in the 1960s. And this is where they asked men conducted quite some time ago back in the 1960s. And this is where they asked men who had already had some sort of cardiovascular event to increase the amount of omega-6 through seed oils in their diet. And what they found was that there was an increased risk in those people who increased their seed oil intake. However, a really important caveat here is that a large proportion of the seed oil that they ate was in margarine spreads, which back in the 1960s was in the form of trans fatty acids, which we've done a previous podcast on, which we

know, yes, are bad for us if they're industrially produced. They're not bad for us now because we're not eating them now. And so it was heavily confounded. And this study is used a lot to say, okay, well, the Sydney Heart Study shows you eat seed oils and it's worse for your health. And what you're saying is it actually tells you that if you eat trans fats, it's bad for you. Yes. And it's a 60-year-old study. What do all the more recent studies say about this omega-6 you're talking about? Is it bad for you? So all the recent studies, the epidemiological research shows that as you increase your

polyunsaturated fat intake, you reduce your risk of ill health from cardiovascular disease and so forth. There's also many, many randomized control trials that show that if you increase your polyunsaturated fatty acid intake, you reduce your LDL cholesterol significantly, and it results in a 32% reduction in cardiovascular disease. So you're saying that actually, if you have more of this omega-6, you reduce your risk of things like heart attacks by how much? So some of the data shows up to about 30 percent now obviously it depends on the length of exposure i.e it's not going to happen overnight but the evidence apart from this one study which we know is flawed the overall totality of the evidence is that omega-6 is beneficial for health i do need to caveat that, Jonathan, though, that

there are a very small proportion of the population that have a particular genetic variant that means that they are susceptible to high intakes of omega-6. And it's always important to say, look, I'm talking about averages here. Everyone responds differently, but overall, the majority of people will actually benefit from increasing their polyunsaturated fatty acid intake we seem to have nailed the omega-6 is bad for you claim you mentioned omega-6 to omega-3 yeah i'm scared about going deeper but let's take us to the next level you've explained i think i've got this that the omega-6 is one of these polyunsaturated. So that is like the best of these sort of constituents of a fat. Take us further. What's omega-3?

So I am going to have to get a bit technical here, Jonathan. I have to forward you. I'm nervous, but go for it. I know. So polyunsaturated fatty acids can be separated into two types, your omega-3 fatty acids and your omega-6 fatty acids. Now for those geeks out there like me, the reason they're called omega-3 or omega-6 is about where the double bonds are positioned on the carbon chain of the fatty acid. Don't cut this bit from the episode, Jonathan. I'm not. You're making me think of my son who's just been doing all of his chemistry exams recently and drawing all these little diagrams with C's and things,

which I remember from 30 years ago, went straight in one ear and out the other. But here you're talking about that for real. They mean something. Okay, go on. So we group them differently. So we group omega-3 and omega-6 differently because of their health effects and also because of how they're structured. And there's lots of evidence to show both of these are favorable in terms of health, but for different reasons. However, and this is where it gets slightly technical. In seed oils, you have an omega-6 fatty acid called linoleic acid. And you have also a similar fatty acid in omega-3 oils called alpha-linolenic acid, ALA, that many people might have heard of. Now, what happens is, is both of these fatty acids can be converted into the body to very

long chain versions. Okay, so linolenic acid can be converted into something called arachidonic acid. Okay, bear with me, we are going somewhere with this. Alpha-linolenic acid from the omega-3 can be converted into very long chain versions called EPA and DHA, which are also found in fish oil. Okay, there's enzymes in the body that convert the linoleic or the alpha-linoleic to these very long chain versions, but they compete for each other. This is where this whole theory around the omega-3, omega-6 ratio comes from. And the reason people say the ratio is relevant because these very long chain versions,

so the long chain version of the omega-6, which is the arachidonic acid, and the long chain version of the omega-3, the EPA and DHA, produce special chemical compounds that have pharmacological-like properties. We call them eicosanoids. And they're very special because they're involved throughout the body in hundreds of processes to do with blood clotting, to do with inflammation, to do with how we metabolize, all sorts of different things, et cetera. What we know is that these chemicals produced by the omega-3 fatty acids have quite beneficial effects in our body. They can be anti-inflammatory. They can be anti-coagulatory. So for example, to illustrate this, I think a lovely example I use when I teach this is if you were years ago to go and cut someone's finger, who's one of the Inuits, for example, living in Alaska, who the majority of their fat actually comes from fish oil, it takes them a long time for

their blood to clot because they're producing from these very long chain omega-3 fatty acids, these chemicals that actually are anti-coagulatory, so their blood's not clotting, which can have benefits, can be a problem if you're trying to heal a wound. These special chemicals that come from the omega-6 very long chain fatty acids or arachidonic acid have slightly more pro-inflammatory and pro-coagulatory properties. Okay. So mechanistically, there's a good sound argument to say, oh, if you have more omega-6, whoa, it's going to be more, you're going to be more pro-inflammatory. You're going to be more coagulatory. I, you know, your blood's going to be more sticky. But if you have more omega-3, then hey,

we're going to be anti-inflammatory, we're not going to have sticky blood. So there's a good mechanistic argument for this. However, this doesn't play out in reality. It doesn't play out in RCTs, randomized control trials in human subjects, then actually increasing the amount of omega-6 in your body and also what you consume does not result in any increase in inflammation. It doesn't result in any increase in coagulation, etc. And that's because our bodies are so clever that we have all of these other mechanisms that come into play. What we also know is that even if you increase the amount of the omega-6 fatty acid, that linoleic acid that I said comes from seed oil, then actually it doesn't result in much of

an increase and almost a negligible increase in that arachidonic acid, that very long chain one, which is the one that you need to make all of these compounds. And what's really lucky as well, Jonathan, is that polyunsaturated fatty acids so our omega-3 and our omega-6 we can't make these fatty acids we can only get them from diet so it's one of the few dietary components that we can actually measure in our body and know that that's an accurate reflection of our diet and are are they essential, Sarah? Like you have to get them in your diet or you would die because you can't, I'm thinking about the, again, the example with those certain amino acids and proteins that I've understood there are certain things you just, we can't make there also.

So they're also called essential fatty acids. So polyunsaturated fatty acids are also known as essential fatty acids. We can't make them in our body. We have to eat them. And this is why in our dietary guidelines, there was a specification that we consume a certain amount of these essential fatty acids because we can't make them. Because we can't make them, that's why we can accurately measure how much of these fatty acids people are getting in their diet. So it's the one area of nutrition that actually we can accurately say, okay, we know how much of these fatty acids people are getting from their diet because we can measure it in their tissue. So it's one area of nutrition. I can say to you quite confidently, Jonathan,

based on the epidemiological data, i.e. where we measure people's tissue levels of these fatty acids, we know that they're eating that and we know that what the relationship with disease risk is now sarah i'm hoping you're not going to test me on all of that because i'm super impressed by any of the listeners who's got the full chain that you've just described i think i got the conclusion though which i think you're saying is that there are a bunch of studies out there that would suggest that if you had more of this omega-6, you'd think you would actually have more inflammation in the body because you do these studies like in a test tube or with mice or whatever this is that sort of tells you that this is bad. When you actually look at the results in human beings eating this over time, you're actually

saying you get the reverse of that, that it's actually preventing risk of heart disease. So there's this weird thing where like it seems on the surface it's bad for you, but actually it's good for you. And that makes me think a bit about exercise, which we also talk a lot about on the podcast, where I've heard lots of scientists explain that like in the short term, you're actually damaging your body. Like it's causing you tears and all sorts of like-term information, but actually it triggers all of these processes that actually repair you better than you would be otherwise. And that's why we know that exercise is good for you. Is that an analogy or am I grasping at something that doesn't really fit here? No, I think that's a good analogy. And I

think just to add to the whole omega-3, omega-6 ratio discussion is it's very clear now that as long as you have sufficient intake of omega-3, changing the amount of omega-6 in your diet does not matter. It's not the ratio that matters. What matters is that you should have a sufficient amount of omega-3 in your diet of either at the fish oil level, these long chain, or at that alpha-linolenic acid level, the ALA, which comes from many seed oils, including like flax seed oil, but is also found in some of these other seed oils as well. And so I think that the top line is let's not focus on omega-6 and let's think of just increasing overall our healthy oil intake.

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Okay, let's get back to the show. Amazing. Now I know you had a couple more myths you wanted to crack. Let's do that. But I definitely want to then get onto like practical advice for people thinking about so what does this mean about what i should eat how can i improve my

health because there'll be people listening to this being like yeah yeah but i just really want to know what i need to do sarah okay so the other myth is that it's unnatural i think we've covered that that you know it's gone through all of this refinement process you know you see these images that are often put on of the oil manufacturers and you see these big silver pipes and you see all of these awful kind of chemical names. Based on the current evidence, I don't think there's any downside of the actual processing of these oils, except maybe a very small loss of some of these phytonutrients, these favorable compounds. Then the fourth reason is it's prone to oxidation. These oils that are high in polyunsaturated fatty acids, they have many double bonds, can be prone to oxidative damage,

can be prone to damage from the oxygen that's around us. And that when we heat the oil, this can become more of a problem. And so this is one of the big arguments that's used as well, that seed oils have a large amount of polyunsaturated fatty acids. The double bonds mean they're prone to oxidation. And when you heat them, therefore, it damages the oil and it produces all of these toxic compounds. Does it? No. So I actually did a randomized control trial many years ago that I'd actually forgotten about until I was thinking about this podcast yesterday.

And this is a study that I conducted at King's with 19 healthy males. It was what we call a crossover study. And what we asked people to do is consume a 50 gram fat load containing a fresh seed oil. So this was particularly rich in sunflower oil. It had a few other oils in it. It's the kind of oil that many commercial companies use for deep frying chips, for example. And then we asked them to come back another time and eat this having undergone several heat cycles. What we actually did was we, over 10 days, heated this oil five times a day at very high temperatures with chips because it's the interaction with oxygen. French fries. Yeah, French fries. It's the interaction with oxygen. Yeah, french fries.

It's the interaction with the oxygen plus the carbohydrates, et cetera. And then we took this oil after 10 days, after these five daily repeat fries, and we put it into my test vehicle, which is always a muffin. And then they ate 50 grams of this reheated, refried fat as well. Doesn't sound very appealing. They did it. Now we actually hypothesized that if we fed these individuals this reheated multiple times at high temperature oil, that it would have quite a negative effect on oxidative compounds. And there's a particular measure we use called isoprostanes to measure this, and that it also might affect our blood vessel function.

And we use a measurement called flow-mediated dilation for this. What we actually find is it had no effect. There was no difference between the fresh oil or this rather nasty-sounding oil that we'd repeat fried on our measurements of these oxidative compounds. It's a measurement of the oxidation of the fat or on how the blood vessels functioned over that eight hours after consuming it. So I was surprised. It doesn't really matter in real life is what you're saying. It doesn't matter in real life. It doesn't matter at the levels at which we typically fry our food. What I would say is obviously this is one study.

Most of the evidence out there that is similar to this also shows similar results. But what I would suggest to people is that they don't repeat fry over 10 days using the same oil. It's best to use fresh oil where they can. Brilliant. Thank you, Sarah. Well, I think I'm sitting here feeling like seed oils don't sound like anything to be scared of. And in fact, it sounds like some seed oils can be good for us, but they're not all equal. Could we maybe switch now to the actionable advice? You're saying we're surrounded by these oils. What should people do?

Let's say they want to say, I'd like to be healthier. What does that mean? How do they think about these different oils? And you mentioned them being also in a lot of food products. So maybe we start with what you're cooking with, which you're aware of, but it sounds like actually it's a bigger discussion than that. Yeah. So I think that we need to be aware that about 60% of the seed oils that we have are coming

from processed foods. It's the other 30 to 40% that we might be adding ourselves. And it's difficult to control what manufacturers are putting into foods. I would say it's not a concern that the seed oils are in these foods. I'd say it's a concern of the other ingredients that are in these foods if we think then what we can do in terms of the food this is the oils that we're using to cook with i think this is where it becomes personalized jonathan because what we do know is that if you have high cholesterol having a high polyunsaturated oil such such as sunflower oil, for example, if you remember, I said that's got higher polyunsaturated fatty acids compared to, for example, rapeseed canola oil. We know that polyunsaturated fatty acids have a very potent

LDL lowering effect. So they lower our bad cholesterol, our LDL. So if I was to suggest to someone who has a high ldl cholesterol i would say that it would be beneficial to use a high polyunsaturated fatty acid oil i would like to caveat that though with saying that we know that extra virgin olive oil is that the king the queen of oils now extra virgin olive oil doesn't actually have that much polyunsaturated fatty acid. It has a lot of the monounsaturated fatty acid that does lower bad cholesterol, but nowhere near to the same extent as polyunsaturated fatty acids. But it's got all of these other wonderful compounds, these polyphenols that will have a beneficial effect.

So if I was someone that had high cholesterol, I would say use a mixture because you want to get the benefit of extra virgin olive oil, of all of these wonderful polyphenols. But I'd also want to get the LDL lowering effect of a high polyunsaturated oil as well. soybean or canola or rapeseed that therefore swap into sunflower or indeed, obviously more expensive through to extra virgin olive oil, that's a change that would be beneficial? So soybean oil does actually have quite a large amount of polyunsaturated fatty acid. It's the rapeseed oil that has the lower level, hence why it's so good for cooking because it's quite stable with a higher monounsaturated fatty acid. So I think both soybean oil or sunflower oil, both of those have sufficient polyunsaturated fatty acids to have a beneficial effect on our LDL cholesterol. I'm not saying though that rapeseed and canola oil won't be beneficial. They still have a reasonable amount and they

also have monounsaturated fatty acids, which will have some lowering effect. So definitely nothing to be afraid of, but there is a possibility you can make that swap and you can have more benefit. Yes, absolutely. And when you were talking about finding these seed oils in our food, I know you said right at the beginning, like palm oil is actually the most frequently used oil in all of these ultra processed food, but it's not a seed oil. You said, don't worry too

much about having seed oils in your food. Do you worry about palm oils in your food or is that, would you actually, that's worse and you would rather see like the seed oil is better than the palm oil? So seed oil is definitely better than the palm oil. I've actually conducted many, many randomized control trials looking at palm oil. I conducted a study where I compared palm oil with a high monounsaturated fatty acid sunflower oil. So it had a similar composition to rapeseed canola oil. And what we saw was there was quite a large difference in terms of the impact that palm oil had, which was unfavorable on blood lipids, on your LDL cholesterol, and so forth. And so I would say from my own research, but also many other studies out there,

hands down, these seed oils are better than the tropical oils, which include palm oil, coconut oil, and so forth. I think while we talk about soybean oil, something that's really important to mention for US listeners is a very large proportion of soybean oil that goes into their food actually undergoes an additional processing technique. And this processing technique is called full hydrogenation and a very large proportion undergoes this and what this process does is it converts a liquid oil into a hard fat and so it will still be labeled soybean on the back of pack but it will have undergone this process of hydrogenation and so for many food applications so for cakes and pastries biscuits for, for example, where you don't particularly

want to pick up a biscuit and have a load of soybean oil dripping out where you need a hard fat, the soybean oil will have been modified to become hard and often mixed together with normal soybean oil with this hydrogenated hardened soybean oil. Which doesn't sound good, Sarah, but earlier you were telling me that I didn't need to worry so much about this extraction. Is this full hydrogenation leaving the soybean oil as healthy as it was before, or is this now causing it to be less healthy? So we've actually done a podcast, Jonathan, I don't know if you remember, about a year ago, all around the process around hydrogenation and trans fats,

which is where the term hydrogenation is often thought about. The food industry can use a process called hydrogenation to change a liquid oil into a hard fat. Years ago, we used a process called partial hydrogenation, which created trans fats, which we know are bad for us. We don't eat them anymore. This is not used anymore. But what is used in the US is this process of full hydrogenation. It's very different to partial hydrogenation. It doesn't produce trans fats, but it basically converts the unsaturated fatty acids in soybean oil, so that monounsaturated fatty acids, into a saturated fatty acid. The saturated fatty acid it converts to, we know that that particular one has a cholesterol neutral effect.

It sounds like it is worse than it was before in terms of the health impact, given what you're describing before. Is that right? But it's not something to be terrified of. You're pushing me to make a call on this and i'm happy to jonathan i think based on this is an area that i've done quite a bit of research i would say that based on all of the studies i've run and other people have run soybean oil in its natural state as a oil that's okay gone some refinement, but hasn't been hydrogenated, is better for you than soybean oil that's been hydrogenated. But I wouldn't say that soybean oil that's been hydrogenated has an unfavorable effect based on current evidence. But again, it's one of these, watch this space.

Do you know someone who's stressed about seed oils? How about you share this episode with them right now so they can be more informed? Understood. So I think you're saying that we talk about this a lot, right? There's lots of foods which are neither particularly harmful nor particularly full of things that are going to benefit your health. And I think you're saying you're actually coming through being pretty positive about seed oils, right? You're saying that a lot of them can really be quite helpful for our health. You're saying in that change where the food industry changes this to a solid in order to make this like lovely cake that lasts forever sitting on the shelf or whatever, unsurprisingly, not many people listening to this will be surprised to hear that probably in general, the cake and pastry and the ultra processed food is not very good for you. You've lost the healthy elements that are protecting us in order to allow it to sit there on the shelf forever. Yes. So it's better to have the original

soybean oil than the hydrogenated soybean oil. This isn't relevant to the UK. We don't use the process of full hydrogenation because there was such poor consumer acceptability of the word hydrogenation because of the trans fats kind of scandal. So it's not relevant to the UK, but it is to the US. I had a couple of questions that I know I'm going to get in so much trouble with listeners who haven't made sure I've got a really clear answer. And you touched on this, but I want to ask it really explicitly. When cooking, if you heat your seed oil above a certain temperature and you see it smoke, has that immediately become harmful? You need to throw it away, start again. You've done something that now this is going to hurt your health, hurt your health of your family. Okay. The worst thing that's going to happen is it will taste pretty rubbish. The second worst thing that's going to happen is you will have deactivated

some of the beneficial compounds that are found in seed oils. So you might have degraded or lost some of the vitamin E, for example. You might have lost some of the polyphenols if that seed oil has polyphenols. You might have degraded some of the phytosterols, for example. Okay. In terms of the generation of harmful compounds, if you repeatedly, repeatedly refry at very high temperatures, you do get generation of some compounds. We call these polar compounds or peroxides. But it's very difficult to generate these through normal cooking processes that you would do at home even if you're burning the oil. Unless you're repeatedly burning it, saving it, leaving it out in the air all day, reusing it the next day, the next day, the next day, I wouldn't worry. And I mean, the cooking oil study

that I referred to that we conducted, I think is a good example of why I wouldn't worry. Now, that's not to say that you might get some high street food chains that are using bad quality oil that are used repeatedly, reusing it over weeks and weeks there it might be a problem but i'm saying for the majority of people and how you cook at home i don't think it's an issue no i think that's incredibly clear then the final question was sarah if i want to just choose the best oil for my health so let's assume that price isn't really the driving issue I'm choosing this oil for my health like what's my what's the best thing and I'm seeing things like avocado oil and very other like sort of like sort of very rare sounding oils which are very expensive but have all of these

claims that they're the best is that what I should be choosing if I'm really trying to optimize my health? Okay. So if you were trying to optimize your health, I would suggest extra virgin olive oil as the go-to oil. If you're trying to lower your cholesterol, I would suggest using extra virgin olive oil where you want the flavor and then maybe sunflower oil in addition to that. I think that we do need to think about the flavor component here, Jonathan. I know you're a great fan of extra virgin olive oil. And while I think it's undoubtedly the best oil, it does have a strong flavor. You fry your eggs in extra virgin olive oil. I can't find my eggs in extra virgin olive oil because I want to taste the egg

and all I can taste is the extra virgin olive oil. I've been to a restaurant recently. They served me a cake made with extra virgin olive oil. It was revolting. Tim liked it, but no, not for me. Now in that instance, then choose an oil that has very limited little flavor. So that's where some of these seed oils are great, particularly the ones that have gone through these refinement processes. So that's why sunflower or these seed oils are great, particularly the ones that have gone through these refinement processes. So that's why sunflower or soybean oil, they actually have very little flavor. So I think if you want a flavorless oil, they're quite good.

With regards to avocado oil, I mean, have you seen the price of it? I have. It's ridiculous. It is. You said, let's forget price. There are no RCTs looking at the health effects of avocado oil, except one where they compare it to butter and all sorts of nasties. So that's just not a fair comparison. So I'm not even going to refer to that. Based on what I know is in avocado oil,

I don't think there would be any additional benefit of the avocado oil beyond having, for example, a good quality canola rapeseed oil. Certainly, I don't believe it would be better than extra virgin olive oil. Happy to be proved wrong in 10 years if someone's going to do some RCTs on this, but there's no evidence to support it at the moment. That's incredibly clear. Sarah, thank you so much. I'm going to try and do a summary and we'll see whether I've managed to hold this in my head for the duration of this podcast. Please correct me if I've got it wrong. It's definitely got a bit complex in places. So instead of if I say like seed oils, actually what they sound like, they're like seeds that are crushed to get the oil out. They've been growing enormously as part of our diet over the

last 50 years. We do use them sort of in our cooking, where it's really obvious that we're pouring them in. But actually, I think you said like 60% of our intake is in this processed and ultra-processed food where it's sort of a bit hidden. You explained that when we think about fats, we can think about them as being made up of these types of fatty acids. Sarah's looking me carefully here. I'm like, I've really got to try and get this right. There are three main groups of these types of fatty acids. Saturated, which has no double bonds.

That's sort of the worst. We know that's like red meat and butter and things like this. Mono-unsaturated, which is one double bond, which has sort of got this thing that's somehow open in some way. And then polyunsaturated, which has got two or more of these bonds. And basically, as I described those three, they get better and better for your health. And then there's evidence that both monounsaturated and polyunsaturated is good for you. And then these combine together in some very complicated way that you were explaining. And the other key thing I think that I took away is within polyunsaturated, actually there's two big groups of that. One is omega-6 and one is omega-3,

and these are called essential fatty acids. We have to eat those or we will die. So we need that in our diet. So this idea that you can eat no fat isn't possible because you would die because you wouldn't get these essential fatty acids. Correct. Okay. And then you explained like once you understand this, many of the reasons why people are scared of seed oils don't make sense. So firstly, you said, yes, it's true. We've eaten a lot more seed oil over the last 50 years and we're all much more unhealthy, but it's not because of the seed oil. And in fact, the evidence is that if you eat more of the omega-6, then actually that is good for your health. It will reduce your risk of heart disease. In fact, you said there was

evidence you could reduce your risk of heart disease by up to 30% with the benefit of this omega-6. And I think you said the omega-3 is even better for you. Is that right? It's better for you for some aspects of heart disease, but it doesn't have such a good effect on lowering cholesterol. Got it. But okay. And it has effects only for heart disease or omega-3 is also helpful for health more broadly? There's quite a lot of emerging evidence given its anti-inflammatory properties, that it can also be beneficial for many other chronic conditions that are underpinned by inflammation. Got it. So basically they're both good for you. Omega-6 very much about heart disease,

omega-3 because of inflammation, probably broader set of things and benefits. You shouldn't worry about the fact that these seed oils have like a high ratio of omega-6 to omega-3. This is one of these examples that you talk about often where you can do a test in a lab where it looks like something's really bad, but then when you actually look at what happens with human beings, you get sort of the reverse results, which is why science of human health is so complicated. So don't worry about that. You discussed the processing.

It is true that you have to go through this like industrial processing for these oils if they're not cold pressed. They don't have as many as the healthful properties as a cold pressed oil, but actually basically you're saying the end result is still like the natural oil. It's not very much worse. You've done tests where you look at them and you can't see any difference in reality in real life. So again, there are many things to worry about. This is not something you think that people listening should worry about. And then the last thing about these myths was don't worry about heating these things above their smoke point. The worst that's going to happen is it's going to taste not as good as it would do otherwise. You're not going to cause some sort of terrible health impact by this. And therefore, you don't need to worry about

the fact that some of these oils might have a lower smoke point than elsewhere. Correct. Although I wouldn't encourage repeatedly using oil that has got to the smoke point repeatedly. If you do that, don't use it again. But if it happens at the point that you're making your pancake or whatever, just don't worry about it. Certainly don't throw the food away that you hide with it. That's great. Thank you. I think that's really clear. And then the conclusion then about what you should do, I think was quite straightforward, actually.

You're saying that in terms of what we're cooking with, the soybean or the sunflower oil are both really good fats with which, really good oils with which to cook. That canola or rapeseed, it sounds, is not as good. So unless you've got this very strong reason why you're doing that, you could swap out to one of those other two for what you're doing at home, and this is going to be better. But you don't need to worry about it. It's not bad for you.

In fact, you're pretty positive about it, but there's quite an easy swap there. If you are really thinking, though, about how you would want to optimize your health, you're saying like the extra virgin olive oil is definitely better. And so the decision there is really let's sort of use the extra virgin olive oil, except for places where the taste doesn't really work for you. In which case, ultimately, you don't want to eat the cake that tastes of olive oil unless it's meant to be an olive oil cake. So be aware of that. And all of

these are much better than palm oil. And if you actually turn over the back of the pack of the food that you're probably getting from the grocery store, you're going to find an enormous amount of palm oil into it. And I think we will do another podcast around that because Sarah is looking more and more unhappy every time I say the word palm oil. You're not a huge fan of that in terms of its impact on your health. So I have spent many years comparing palm oil to other fats. I've actually received a lot of research funding from the palm oil industry, and I always like to declare any conflict of interest. But yes, I think a really important thing to say, given we have such a mixed audience, is that palm oil is used in the UK in the way that the fully hydrogenated soybean oil is used in the US. So fully hydrogenated soybean oil is used as a hard

fat in the US and palm oil is used as a hard fat in the UK. And in both those cases, these are not as good as the oils before they're treated. Yeah. And I'd like to make another caveat to your sum up, Jonathan, is that I do believe seed oils are still very healthy. So whilst extra virgin olive oil might be better for some of these other compounds, the actual RCT, the randomized control evidence, would show that for many outcomes, seed oils perform nearly as equally as well as extra virgin olive oil. And so for many people, if I come back to the starting point, which is like, I'm really worried that seed oils are toxic. For most people listening to this,

tell me what would happen if they had more seed oil in their diet than they currently have? So assuming the seed oil is coming out of a bottle and not out of a heavily processed unhealthy cake, for example, for the majority of people out there, this will reduce their cholesterol and have a beneficial long-term impact on their health. Which is pretty amazing, right? So basically the story out there is this is really terrible. And in most cases, you probably would have more of that, less bread or cake or whatever, because you're sort of balancing what you eat, you're actually saying they'd be better off. Yes. So apart from this one study that is so full of limitations, the totality of evidence is so consistent that an increase in omega-6 coming from seed oils

improves our health. Sarah, thank you so much for taking us through that. And thank you for setting me right where I've got a bit confused. I think it's pretty eye-opening and hopefully we can have one video on YouTube now that says something different from all the others. Yeah, I'm excited. I'm looking forward to all C-Dolls are toxic influencers hate mail now. I'm sure we'll be fine. Thank you so much, Sarah. Pleasure. I loved having Sarah on the podcast today, and I hope you learned something new from her. My biggest takeaway is that there's probably nothing to worry about when it comes to seed oils.

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