ZOE Science & Nutrition - Recap: The truth about seed oils | Prof. Sarah Berry

Episode Date: September 9, 2025

From Instagram reels to viral tweets, seed oils have become one of the latest nutrition villains. And the fear’s getting real. People are emptying their cupboards, terrified these everyday oils are silently wreaking havoc on their health. So is this panic justified? Or does the science require further scrutiny?  Well, ‘scrutiny’ is Professor Sarah Berry’s middle name! She’s going to cut through the confusion, dig into the data, and tell you whether it’s time to rethink your next stir-fry. 🌱 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 📚 Books from our ZOE Scientists: The Food For Life Cookbook by Prof. Tim Spector Food For Life by Prof. Tim Spector Every Body Should Know This by Dr Federica Amati Free resources from ZOE: Live Healthier: Top 10 Tips From ZOE Science & Nutrition  Gut Guide - for a healthier microbiome in weeks Have feedback or a topic you'd like us to cover? Let us know here Listen to the full episode here

Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're talking about seed oils. From Instagram reels to viral tweets, seed oils have become one of the latest nutrition villains. And the theme is getting real. People are emptying their cupboards. Terrified these everyday oils are silently wreaking havoc on their health. So is this panic justified? or does the science require further scrutiny? Well, scrutiny is Professor Sarah Berry's middle name. She's going to cut through the confusion, dig into the data,

and tell you whether it's time to rethink your next stir fry. 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, and 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. You know, 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 like 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 we've tended to, you know, turn out to be calling ultra-process foods. And other things are incredibly straightforward.

What's the situation for these seed oils? So it is actually, I think, relatively straightforward. forward. 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 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 oils. So it becomes a more efficient way of extracting the oil. At that point, it can no longer be called coal-pressed, and it's 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 techniques are things like bleaching and deodorization. Now, they do sound quite scary. People are thinking probably bleaching, peroxide. It's not as scariest it sounds.

What happens 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 favourable elements in seed oils. 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 coal 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 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 coal-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 maybe are finding coal-pressed oils very expensive because they are a lot more costly to say, OK, they are really, really this much healthier. Got it.

So you're saying there is this industrial extraction process, but, you know, 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 squeeze 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 oxidic 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.

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, that comes from somewhere. What are they worrying about? Gosh, if only I could get on my soapbox now, Jonathan. Honestly, it drives me insane when I see this. And in preparation for this, I did Google on, I went on to the podcast app and I had a look at seedors. And these alarms are like, seeders are toxic.

Seedores are going to kill you. It's absolute nonsense. 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. 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, you know, 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, you know, 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 see, as we call it. So as your intake of seed oil increases, so does the level.

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 causation. 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 for. from these cereal-based 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, are increasing stress, our increase in sleep problems, you know, et cetera, et cetera, et cetera,

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 know, 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, you know, 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 acids, so one of the main fatty acids in these seed oil. 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 mono-ons? 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,

and it is also found in quite high amounts in these other oils like soybean and canola oils. 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 favourable effects on all-cause mortality. So I know you like to refer to that as, you know, how likely is people 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 seed oils are 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 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 increase 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 actually tells you that if you eat trans fats it's bad for you and it's a 60 year old study well 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 much?

So up to, some of the data shows up to about 30%. 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 total The 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. I'll end this recap with something I think you'll like, a free gut health guide created by our team of scientists here at Zoe. Many of us aren't sure how to best support our gut, so we developed an easy-to-follow guide,

complete with tips, recipes and shopping lists designed to help you look after your gut. The guide is delivered straight to your inbox, along with ongoing nutrition insights from Zoe, the Science and Nutrition Company on a mission to transform their health of millions. To get your free gut health guide, just visit you. zoey.com slash gut guide. Thanks for listening.