Seed Oils: Should You Switch to Butter?

We’ve been told that foods like butter and bacon are bad for us — because they're packed with saturated fats. And top dogs in nutrition say that a better option is vegetable oil, like canola oil. But lots of people, including HHS Secretary Robert F. Kennedy Jr., are saying hold on. They're arguing that saturated fats are actually the way to go. And they're claiming that those vegetable oils, aka “seed oils,” are incredibly dangerous. So — who’s right?? To find out, we speak to author and physician Dr Cate Shanahan, professor of nutrition science Jason Wu, professor of endocrinology David Schade, and Dr David Iggman. [REBROADCAST] Find our transcript here: https://bit.ly/SVSeedOils In this episode, we cover: (00:00) Seed oils are the devil (05:35) Is saturated fat killing you? (12:25) Does cholesterol cause heart attacks? (22:02) Do seed oils cause inflammation? (28:00) Are seed oils killing you? This episode was produced by Wendy Zukerman, with help from Joel Werner, Rose Rimler, Nick DelRose and Michelle Dang. We’re edited by Blythe Terrell. Fact checking by Carmen Drahl. Mix and sound design by Bumi Hidaka. Music written by Bobby Lord, Emma Munger, Peter Leonard, and Bumi Hidaka. Thanks to all the researchers we spoke to including Dr Lorena Pacheco, Dr Qi Sun, Dr Tetsumori Yamashima, Dr Idrees Mughal, Professor Rashika Ahmed, Dr Hatem Tallima, Dr Heidi Silver, Professor Ronald Krauss, Dr Yutang Wang, Dr David Sullivan, Professor Peter Clifton, Dr Lee Hooper and others. And a big thank you to Morgen Rockel, the Zukerman Family and Joseph Lavelle Wilson. Science Vs is a Spotify Studios Original. Listen for free on Spotify or wherever you get your podcasts. Follow us and tap the bell for episode notifications. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Wendy Zukerman?

  Hi, I'm Wendy Zukerman and you're listening to Science Fers. And today on the show, we are pitting facts against fats.

• 0:10Wendy Zukerman?

  For years, the top dogs in nutrition have been howling about how foods like butter and bacon are bad for us because they are packed with saturated fats. And instead, they say, we should be eating vegetable oils. These oils are filled with a different combination of fats that experts have told us are good for us. But there's a trend that's popping off right now that says that these top dogs are barking up the wrong tree. And in fact, butter is healthy and those vegetable oils, which are probably sitting on your kitchen countertop right now, are actually incredibly dangerous and might even be killing you.

• 0:57Speaker 01

  Medical science is messed up when it comes to nutrition.

• 1:01Wendy Zukerman?

  This is Dr. Kate Shanahan. She's a family physician who's been raging against the nutrition science machine.

• 1:07Speaker 01

  It's just so wrong. It's morally wrong. It's ethically wrong. It's shocking. And I just, after 20 years, I still haven't gotten over it.

• 1:15Wendy Zukerman?

  Kate has a big problem with vegetable oils that are extracted from seeds, the so-called seed oils. What exactly are the seed oils?

• 1:24Speaker 01

  The problematic seed oils are a collection of eight highly refined industrially processed vegetable oils, specifically soy, safflower, sunflower, corn, cottonseed, canola, and rice bran, and grape seed oil.

• 1:45Wendy Zukerman?

  Kate calls these oils the hateful eight. You might have noticed your olive oil is still fine, but canola oil and soybean oil, they are in the bad books. It's the vegetable oils that are often yellow and come in those giant plastic bottles. And you'll find them in lots of different foods.

• 2:03Speaker 01

  So they are in salad dressing. Your canned tuna, preserved veggies are in, even olives these days are often in soy oil, frozen dinners, gator tots, microwave popcorn, granola, you know, supposedly healthy granola.

• 2:16Wendy Zukerman?

  In a book that Kate wrote on this topic, which really helped kick off this new seed oils trend, she wrote that, quote, "Avoiding vegetable oils is the most important action you can take to improve your health," end quote. Because according to Kate, eating a lot of seed oils produces a ton of inflammation in your body, increasing your risk of an array of diseases, from heart disease to cancer.

• 2:42Speaker 01

  If I were to list all of the diseases you can get by eating seed oils, this podcast would be going on for, until tomorrow.

• 2:53Speaker 01

  There's too many. It's every single one they contribute to.

• 2:57Wendy Zukerman?

  And so, instead of eating these seed oils, Kate wants you to be chowing down on something else: saturated fat.

• 3:05Speaker 01

  The very fats that doctors will tell you to avoid. We're talking about, you know, fatty cuts of meat, like steak and, you know, pork and bacon and dairy fat, like butter and cheese and cream and eggs.

• 3:22Wendy Zukerman?

  This is really the list of like, the demonized list for, this is really like a, a no, no, no, no, no, no, no, no list.

• 3:29Speaker 01

  I know, and, and, you know, dieticians listening to this are probably thinking she's a loon.

• 3:35Wendy Zukerman?

  But Kate went on this diet herself. Seed oils out, saturated fat in. And she said she felt great. She even started putting her patients on this diet. And she told me that she's seen some miraculous things.

• 3:49Speaker 01

  People who've done it feel better and they feel better than ever. They feel younger in their 60s than I did in my 30s. They said that I, I had, I had diabetes and I got off my diabetes medications in a weekend. I had heart failure. I no longer have heart failure. My kidneys were failing. They're better now.

• 4:09Wendy Zukerman?

  And it's not just Kate who's saying this kind of thing. This idea has blown up. People all over socials and podcasts swearing by this diet. And they're saying that you need to stop eating seed oils.

• 4:22Speaker 02

  Seed oils are some of the worst [bleep] things your body can consume.

• 4:25Speaker 03

  These oils are inflammatory. They've been linked to heart disease, cancer. They are poisons, plain and simple. Seed oils are the devil.

• 4:33Speaker 04

  Seed oils are one of the, um, the most unhealthy,

• 4:40Speaker 04

  ingredients that we have in foods.

• 4:45Wendy Zukerman?

  So today on the show, we are finding out what is going on here. Is your canola oil really killing you? And is butter now healthy? It's the ultimate clash of the titans. In one corner, seed oils. In the other, your bacony, buttery saturated fat. Who will win? And I gotta tell you, chewing the fat on this one, I haven't worked on an episode of Science vs. that has upended so many of my views about food. When it comes to this diet, there's a lot of...

• 5:17Speaker 03

  Seed oils are of the devil.

• 5:20Wendy Zukerman?

  But then, there's science.

• 5:24Wendy Zukerman?

  Science vs. Seed Oils is coming up, just after the break.

• 5:34Wendy Zukerman?

  This episode is brought to you by Chase Sapphire Reserve. On this podcast, we sort fact from fiction. So here's a quick truth for you. With Sapphire Reserve, you can spend all around the world. Not only that, but you can earn four times the points on flights and hotels, book direct, and three times the points on dining. Plus, enjoy access to award-winning airport lounges and exclusive restaurant tables. Learn more at chase.com/sapphirereserve. Cards issued by JPMorgan Chase Bank, N A member, FDIC. Subject to credit approval, terms apply.

• 6:13Speaker 05

  Gray roots entering the chat, uninvited? Garnier's got you. Garnier Color Sensation Root Retouch covers up to 100% of grays in just 10 minutes. No ammonia, no mess, and the color lasts up to four weeks. It's as easy to apply as shampoo. Plus, it's vegan and cruelty free. 10 minutes, sensational color, sensational price. With those savings, your next girls' night is basically free. Find your perfect match at walmart.com or at a store near you.

• 6:49Wendy Zukerman?

  Welcome back. Today it's seed oils versus saturated fat. Should you ditch your canola oil, like Kate Shanahan says, and fill your belly with butter and bacon instead? To get to the bottom of this, let's leave Kate for now and go on an adventure to simpler times, where the shoulder pads are sky high and the messages that we got about saturated fat were crystal clear. Back in the 80s and 90s, we were told that eating foods high in saturated fats, so think meats, butter, cream, was one of the worst things you could do for your health. Why? Because these foods raise your cholesterol and increase your risk of heart disease.

• 7:34Speaker 06

  If you eat too much of this, then over time fatty deposits could build up in your arteries and this increases your risk of heart disease.

• 7:41Wendy Zukerman?

  Here's this grim ad from the UK in the 90s. You can see a glass jug filled with fat that someone is slowly pouring down their kitchen sink.

• 7:51Speaker 06

  The saturater fat can clog this pipe. Imagine what it's doing to yours.

• 7:56Wendy Zukerman?

  In the US, this was the vibe. Kendall-looking fellas were mansplaining dietary advice to their ladies.

• 8:04Speaker 07

  Gee, hope that's not full of saturated fat.

• 8:06Wendy Zukerman?

  Of course not. See? Made with sunflower oil, no cholesterol, low in saturated fat. Oh, and in Australia?

• 8:21Wendy Zukerman?

  But song or no song, the message was clear. Saturated fat is bad. So is this true? To find out, we need to meet a new guest. So please, introduce yourself.

• 8:34Speaker 08

  Yeah, sure. My name is Jason Wu. I'm a professor and head of the Nutrition Science Team at the George Institute for Global Health, based in Sydney, Australia. I'm on the land of the Gadigal people of the Uranian.

• 8:46Wendy Zukerman?

  I've always just... Known that saturated fats are bad.

• 8:51Speaker 08

  Yeah.

• 8:51Wendy Zukerman?

  When did you first get the message that saturated fats are bad for us?

• 8:57Speaker 08

  Certainly, it was from a pretty young age as well. You know, I was born in the eighties and my family, my parents, you know, just about every person, when they think about nutrition, around, oh, if I want to be healthy, I've just got to stay away from it. So it's a message that has been around for a long time.

• 9:12Wendy Zukerman?

  Yeah, that message partly dates back to some controversial research from the 1950s, suggesting that some countries where people eat a lot of saturated fat, like the US, Canada and Australia, also have higher rates of heart disease compared to countries where people don't eat that much of it.

• 9:29Speaker 08

  And since then, we've had a whole lot more evidence, which I'm happy to come into, that that sort of suggested that the story is not as simple as it what it seemed.

• 9:37Wendy Zukerman?

  So let's get into this evidence. Saturated fat is a type of fat that's generally solid at room temperature. So think of chunks of lard, coconut oil, palm oil, and of course, butter.

• 9:51Speaker 08

  Butter is sort of what's traditionally held up as the poster child of what to avoid, right?

• 9:56Wendy Zukerman?

  It is a big chunk of saturated fat, right?

• 9:59Speaker 08

  Right, of animal-based, right, right, saturated fat.

• 10:03Wendy Zukerman?

  If you imagine a stick of butter, half of that is literally saturated fat. And several years ago, Jason and his colleagues wanted to see if butter was really that bad for us. So they scoured through the literature, grabbing all these studies that had looked at whether people who ate a lot of butter had higher rates of things like heart disease, stroke, diabetes, and even premature death.

• 10:27Speaker 08

  We don't just cherry pick one study, two studies. So we haul these kinds of studies together and say, if you look at them all together, what does it tell us?

• 10:35Wendy Zukerman?

  They found nine studies that included more than 600,000 people, who've been followed for many years, and every now and then quizzed about what kinds of foods they were eating, and particularly how much butter they were popping in their pie hole. By the end of the study, nearly 10,000 people had heart disease, and more than 28,000 had died.

• 10:59Wendy Zukerman?

  So, did the butter boys fare worse? Well, let's start with the worst possible thing here. Premature death.

• 11:08Speaker 08

  People who reported eating more butter had an ever so slightly elevated risk of total mortality.

• 11:15Wendy Zukerman?

  Okay.

• 11:15Speaker 08

  For every serve, so about 14 grams of butter per day, it's about a 1%, barely statistically significant elevated risk of premature death.

• 11:24Wendy Zukerman?

  Got that? Eating a bit of butter every day increased your risk of dying prematurely by 1%. So it's clearly not arsenic here. And then, when we zoom in on heart disease, what was the link between getting a heart attack or stroke and eating butter?

• 11:43Speaker 08

  Zero, absolutely no relationship between eating more butter and heart disease risk.

• 11:48Wendy Zukerman?

  Oh, wow. With diabetes, eating a little butter actually lowered your risk of getting it by around 4%, which I couldn't believe.

• 11:57Speaker 08

  So.

• 11:58Wendy Zukerman?

  Lower risk of type 2 diabetes.

• 12:00Speaker 08

  You heard that correctly. So it's a very, very small amount. Just to give you something in comparison, in similar kinds of analysis, looking at things like sugary drinks, right? Coca-Cola, Pepsi, every one serve per day of, say, a can of Coke is related to nearly 20% higher risk of type 2 diabetes. So just to give you a sense of.

• 12:18Wendy Zukerman?

  Just to say, yeah, yeah, right. And this was like in the 1%, 2% in either direction.

• 12:23Speaker 08

  Right, yeah, yeah.

• 12:25Wendy Zukerman?

  In 2016, Jason and his team published this study and gave it the title, "Is Butter Back?" And some scientists couldn't believe it.

• 12:34Speaker 08

  When it first came out, it was very controversial. A lot of people sort of took us to task and said, oh, look, you know, this is, I mean, butter is clearly bad for you. And we said, well, we've just shown you the evidence. And if you've got other evidence you would like to present to us and say how terrible it is, you know, like on the realm of such sugary drinks, I'm all for it. Please show us that data, please show us that evidence. And none were really particularly forthcoming.

• 13:00Wendy Zukerman?

  So, that is butter. Now, when you zoom out to all kinds of foods that are rich in saturated fat, so not just butter, but also stuff like cream, lard, bacon, beef, pork, sausages, the research is a little more mixed. Like, one big review did find that, overall, shoving less saturated fat down your gob could cut your risk of heart disease by a bit.

• 13:24Wendy Zukerman?

  But still, the message coming out of science right now is that saturated fat is not the big killer that the 80s led us to believe. Turns out it was the shoulder pads all along.

• 13:39Wendy Zukerman?

  But this did make me wonder, what does this mean for that whole story that we've been told about why saturated fat is bad? Like, you know, that foods like butter and bacon clog our arteries with dangerous cholesterol and then bam, heart attack. Like, is that whole story a lie? Because some headlines seem to be suggesting, yeah.

• 14:07Speaker 09

  High cholesterol may not mean heart disease in your future after all. Most Americans believe heart attacks happen when cholesterol clogs your arteries. In reality, cholesterol is actually not the main culprit.

• 14:22Wendy Zukerman?

  Some are even saying that cholesterol is healthy for us. So what is going on here? To find out, I called up David Shade, a professor of endocrinology at the University of New Mexico Health Sciences Center on the other side of the globe.

• 14:39Speaker 10

  Are you still in Australia?

• 14:40Wendy Zukerman?

  I am still in Australia.

• 14:42Speaker 10

  Wow, we're doing this across the world. This is amazing.

• 14:45Wendy Zukerman?

  It's good, right?

• 14:46Speaker 10

  I've never done it before, so this is exciting to me.

• 14:50Wendy Zukerman?

  And it was exciting for me to chat to David because I wanted to know, is it possible that cholesterol is good for us?

• 15:00Wendy Zukerman?

  And David was like, well, duh, yeah. Cholesterol is super important.

• 15:06Speaker 10

  So we're all made up of billions of cells, right? Skin cells, heart cells, muscle cells. And something has to keep those cells together. Otherwise, we'd all be a pile of jello, right? But we're not a pile of jello.

• 15:21Wendy Zukerman?

  The reason we are not a pile of jello is partly thanks to cholesterol, which is this waxy, yellowish fat that hangs out in the lining of our cells, giving them structure. We also use cholesterol to make a bunch of hormones like cortisol and testosterone.

• 15:38Speaker 10

  So cholesterol is absolutely critical.

• 15:41Wendy Zukerman?

  And so then tell me, how did cholesterol get such a bad name?

• 15:45Speaker 10

  Okay, so a little bit is great, but too much is bad.

• 15:50Wendy Zukerman?

  So David tells me, here's the deal. To travel around your body, doing all of its important things, cholesterol travels in these little balls of fat via the highway that is your blood. But when you have too much of this particular kind of cholesterol, called LDL cholesterol, swimming around in your blood vessels, some of it can get trapped in these teeny tiny holes in the lining of your arteries. And this becomes an issue. Now, we used to think that cholesterol literally clogged up your arteries. But now we know that's not entirely true.

• 16:29Wendy Zukerman?

  It's actually that your body tries to get rid of that nasty cholesterol with the help of these immune cells called macrophages.

• 16:37Speaker 10

  Okay, those cells are really scavenger cells. They take up any bits of old cells around, dead things, they're scavengers. And if they see little droplets of cholesterol, they take it up.

• 16:49Wendy Zukerman?

  They're like little Pac-Man, like Pac-Man, like.

• 16:52Speaker 10

  Exactly, exactly. And they eat cholesterol. And then, but they eat so much that they die, basically.

• 17:00Wendy Zukerman?

  And what can happen is that if you have more and more bad cholesterol in your blood, you end up with this big gross pile on.

• 17:08Speaker 10

  That's exactly, that's exactly what happens. They pile up. You can see these yellow streaks in the arteries. And those are macrophages, just practically dead, just full of cholesterol. That's bad news.

• 17:21Wendy Zukerman?

  Eventually, that big globby mess of Pac-Man cholesterol and other stuff builds up and up and up, forming what we call a plaque. And that can rupture or explode into your blood vessels, causing a heart attack.

• 17:37Wendy Zukerman?

  So, having too much LDL cholesterol, or bad cholesterol, does up your risk of getting heart disease. And science has shown this again and again and again. And the thing is, eating a diet that's high in saturated fat, the kind of diet that Dr. Kate Shanahan, who we met at the start of the show, is promoting, on average, that kind of diet, it actually increases the amount of LDL cholesterol swimming in your blood. And in fact, on this diet, Kate's bad cholesterol went up. My cholesterol levels have gone through the roof since I started this.

• 18:15Speaker 10

  Yeah, I have a patient like that.

• 18:17Wendy Zukerman?

  And David has seen this as well. So, according to the CDC, a healthy LDL level is roughly 100.

• 18:24Speaker 10

  And then we're talking about their LDL cholesterol went from 110 to 430.

• 18:29Wendy Zukerman?

  Wow.

• 18:30Speaker 10

  Yeah, she went on that kind of diet.

• 18:32Wendy Zukerman?

  Really?

• 18:33Speaker 10

  And it zoomed way up to 430. Yeah, that's terrible.

• 18:38Wendy Zukerman?

  The big question is, if eating saturated fat ups your bad cholesterol, and bad cholesterol ups your risk of heart disease, then why aren't we finding that butter and even saturated fat more generally are that bad?

• 18:55Wendy Zukerman?

  Well, here's how David sees it.

• 18:57Speaker 10

  You know, on the field of heart disease, there's a bunch of players. There's smoking is a player, hypertension's a player, and then there's saturated fat. Well, it's about a 1% player out of the whole 100% field. It's not an important player.

• 19:15Wendy Zukerman?

  And there's a couple of reasons why saturated fat isn't an important player here. One is that what makes up your bad LDL cholesterol isn't just how much saturated fat you eat. In fact, a huge chunk of your LDL cholesterol is actually produced by your own body. And some people, thanks to their genes, just naturally have very high LDL levels. And then there is this super interesting idea that I actually had no idea about until I started researching for this episode. So do you remember how this bad cholesterol gets into the little holes in the lining of your arteries?

• 19:57Wendy Zukerman?

  And that kicks off the process with the Pac-Man and the big globby mess that can eventually lead to a heart attack. Well, what we are learning is that there are different kinds of bad cholesterol that come in different sizes.

• 20:13Speaker 10

  As with everything else, there are different sizes of people, there are different sizes of dogs, there are different sizes of cholesterol particles that circulate around in you.

• 20:23Wendy Zukerman?

  Okay.

• 20:24Speaker 10

  Now, it turns out, since the cholesterol has to go through these pores, the little ones go through much easier than the big ones. So the little ones are much more dangerous than the big ones.

• 20:35Wendy Zukerman?

  You can think about it like this. The smaller the dog, the raddier it tends to be. The smaller the cholesterol, the more dangerous it tends to be. And research is suggesting that the kind of cholesterol that saturated fat ups in your blood is kind of like a pug-sized cholesterol. So it's not great, but it's not some sh** chihuahua.

• 21:02Wendy Zukerman?

  And then finally, there's something else going on here. When you eat foods with saturated fat, you're not just eating fat. Like, if you think of a stick of butter, there's other stuff in it, like omega-3 fatty acids, calcium and vitamin D, all of which might play a role in reducing your risk of heart disease. So maybe when you eat some of these saturated fatty foods, you might up your bad cholesterol, which increases your risk of heart disease. But then you might end up with some more nutrients, which lowers your risk of heart disease. So at the end of the day, when it comes to butter, here's how Jason sees it.

• 21:44Speaker 08

  And I think this is a really important point. And no point in time do we say that therefore, go and knock yourself out, eat as much butter as you like, right? Because that clearly also isn't what we found. We basically found a somewhat neutral to marginal effect of butter.

• 21:59Wendy Zukerman?

  Neutral to marginal effect.

• 22:03Wendy Zukerman?

  Perhaps a Jurassic Park analogy might help us here. Saturated fat is no T-Rex. It's not a big killer. But it's not Laura Dern either. It's more of a Jeff Goldblum. You know, like a bit creepy, but also kind of fun.

• 22:22Wendy Zukerman?

  And you know, if you personally have a high risk of heart disease, then cutting back on saturated fats is something that you can do to reduce your risk. But bottom line, I think Dr. Kate Shanahan, who we met at the start of the show, she has a point when she says that these foods aren't as bad as we've been told they are.

• 22:43Wendy Zukerman?

  But to Kate, the real velociraptor in the kitchen are seed oils.

• 22:50Wendy Zukerman?

  She says that it's these oils that are causing an array of diseases inside your body. And with the help of thousands of muffins and a whole lot of butt fat, we're gonna find out if she's right after the break.

• 23:12Speaker 11

  Are you looking for support in your weight management journey? Zepbound Terzepatide may be able to help. Zepbound is a prescription medicine used with a reduced calorie diet and increased physical activity to help adults with obesity, or some adults with overweight who also have weight-related medical problems to lose excess body weight and keep the weight off. Zepbound is approved as a 2.5, 5, 7.5, 10, 12.5, or 15-milligram injection. Zepbound contains Terzepatide and should not be used with other Terzepatide-containing products or any GLP-1 receptor agonist medicines. It is not known if Zepbound is safe and effective for use in children. Don't share needles or pens, or reuse needles.

• 23:54Speaker 11

  Don't take if allergic to it, or if you or someone in your family had medullary thyroid cancer, or if you've had multiple endocrine neoplasia syndrome type 2. Tell your doctor if you get a lump or swelling in your neck. Stop Zepbound and call your doctor if you have severe stomach pain or a serious allergic reaction. Severe side effects may include inflamed pancreas or gallbladder problems. Tell your doctor if you experience vision changes before scheduled procedures with anesthesia. If you're nursing, pregnant, plan to be, or taking birth control pills. Taking Zepbound with asylphonal urea or insulin may cause low blood sugar. Side effects include nausea, diarrhea, and vomiting, which can cause dehydration and worsen kidney problems. Talk to your doctor.

• 24:35Speaker 11

  Call 1-800-545-5979, or visit zepbound.lily.com.

• 24:43Speaker 05

  Gray roots entering the chat? Uninvited? Garnier's got you. Garnier Color Sensation Root Retouch covers up to 100% of grays in just 10 minutes. No ammonia, no mess, and the color lasts up to four weeks. It's as easy to apply as shampoo. Plus, it's vegan and cruelty-free. 10 minutes. Sensational color, sensational price. With those savings, your next girls' night is basically free. Find your perfect match at walmart.com or at a store near you.

• 25:13Speaker 05

  Gray roots entering the chat, uninvited? Garnier's got you. Garnier Color Sensation Root Retouch covers up to 100% of grays in just 10 minutes. No ammonia, no mess, and the color lasts up to four weeks. It's as easy to apply as shampoo. Plus, it's vegan and cruelty free. 10 minutes, sensational color, sensational price. With those savings, your next girls' night is basically free. Find your perfect match at walmart.com or at a store near you.

• 25:44Speaker 12

  From the creators of Zootopia and Frozen comes Disney's Hext. Welcome to Hext and enter the world of witches, where it was foretold that an ordinary girl would become an extraordinary witch and save the world of magic. Disney's Hext arrives in theaters this Thanksgiving.

• 26:09Wendy Zukerman?

  Welcome back. Today on the show, we're looking into this new diet that wants you to throw out your seed oils. So think canola oil, corn oil, that giant bottle of yellow stuff in your kitchen? Get rid of it, people are saying. Why? Because they are toxic. And if that's true, it's troubling. Because in the US, consumption of seed oils has more than doubled since the 1960s. Dr. Kate Shanahan, who's the queen of this new diet, says that as we've been eating more and more seed oils, our rates of certain diseases have gone up and up. There's this graph that she uses on her website and book, and it's flown around the internet,

• 26:50Wendy Zukerman?

  that shows seed oil consumption skyrocketing alongside various diseases, like obesity and cancer.

• 26:57Speaker 01

  We have the entire population of the United States consuming more seed oils than ever, every year.

• 27:05Speaker 01

  How can you explain that if seed oils are healthy? How do you explain that? Everyone's asking us to ignore this. It's like the man behind the curtain on The Wizard of Oz. Don't pay any attention to what you see with your own eyes.

• 27:21Wendy Zukerman?

  Now, this is of course just a correlation. And you know, one big reason why cancer rates are going up is because our population has been getting older and older. And Kate told me that she knows correlation doesn't equal causation. But she's also pretty convinced that seed oils are mucking up our bodies. And so what diseases do you think eating seed oils are linked to? Can you list them off for us?

• 27:47Speaker 01

  So just to list some diseases that are that are common and I see a lot. Well, actually, let's start with the good news. Let's give some little good news here. Things that go away really quickly when you stop eating seed oils are skin conditions like acne, inflammatory skin conditions like acne, and eczema, and recurring hives. Inflammatory digestive systems get a lot better. And even irritable bowel, even celiac disease. You know, I think brain cancer, dementia and Parkinson's. Heart attacks, they cause heart attacks. So there's nothing that they don't cause. And that means there's nothing that won't get better, at least a little bit, and maybe a whole lot, when you stop eating seed oils.

• 28:29Wendy Zukerman?

  So in Kate's mind, this long list of diseases are connected by one thing. Inflammation. And based on quite a lot of theory, Kate reckons that by looking at the biochemistry, you know, examining what makes up these seed oils at a molecular level. She thinks that when we burn these seed oils for fuel in our body, it releases free radicals that she says are bad for us.

• 28:56Speaker 01

  And can release very dangerous particles into our bodies after we've eaten these things in large amounts.

• 29:04Wendy Zukerman?

  And this, she says, can lead to inflammation. Now, when we asked Kate for her best evidence that seed oils are linked to all those different diseases, a bunch of the papers that she sent us weren't actually about seed oils, but studies connecting oxidative stress, inflammation, and certain illnesses.

• 29:25Wendy Zukerman?

  But if you look in the literature, there have been other theories about whether the fats in these seed oils might cause inflammation. And all over the internet, people are saying that the way that we refine and make these oils puts a bunch of toxins in them that then are dangerous when we eat them. So what we've got is a lot of theory. But now it's time to put it to the test. So me, David Iggman, he's a doctor and researcher at Uppsala University in Sweden. And he has gone to heaven and earth to find out what is up with these fats. Or at least, his team did a lot of baking.

• 30:03Speaker 13

  We made a lot of muffins, like thousands and thousands of muffins. But we changed the flavor. Like every week, we had some chocolate, some vanilla, some cinnamon.

• 30:14Wendy Zukerman?

  David and his team baked all of these muffins because he's done a series of studies to find out if you feed people muffins that are packed with either seed oils or saturated fat, what happens? Does inflammation in their body go up or not? So for example, in one study, he got around 60 people to eat muffins, some which were made with palm oil, which is a saturated fat, and others were made with sunflower oil, which is a big no-no, according to Kate.

• 30:44Speaker 13

  So they were like very similar in all aspects, except just what kind of fat we put into them.

• 30:50Wendy Zukerman?

  So people ate these muffins for eight weeks. And throughout the experiment, David and his team would then test a bunch of things in their body, including markers of inflammation. Now, if seed oils are indeed bad for us and cause inflammation, then you'd expect that the sunflower oil group would see a bump in their inflammatory markers, right? In your study, what did you find? Did the sunflower oil eating group have more oxidative stress?

• 31:20Speaker 13

  No, we measured no increases in inflammation, this markers.

• 31:25Wendy Zukerman?

  And in fact, a big review paper on this topic said that there was, quote, "virtually no evidence" that adding seed oils to your diet bumps up your inflammatory markers.

• 31:37Wendy Zukerman?

  I talked to Kate about the muffin study.

• 31:40Speaker 01

  So there's a lot there to unpack. So for one thing, it was an eight-week study. That's not long enough. It takes years before the body composition will change. And secondly, we're not talking about real endpoints when we're talking about inflammatory markers. Inflammatory markers are blood tests. We don't treat blood tests in medicine. We treat human beings who have real, physical feelings.

• 32:07Wendy Zukerman?

  And this brings us to a completely different study that David was a part of. I asked him about it. So what did you do? You took samples of butt fat from these elderly men?

• 32:19Speaker 13

  Yeah, it was buttock.

• 32:22Wendy Zukerman?

  So in this study, David's team analyzed these fat samples, which had been taken from the buttocks of more than 800 older Swedish men and then stored for around 15 years. Were you excited when you found out there were these samples in the fridge? Like, that's a...

• 32:41Speaker 13

  We just found this fridge lying around with all this buttock fat samples.

• 32:50Speaker 13

  And that's not quite how it happened. But yeah, it's a cool study. I mean, it's very impressive that we have all this data.

• 32:58Wendy Zukerman?

  And to understand what David is doing with all of this data, you need to know that seed oils have a bunch of these particular kind of fats in them called polyunsaturated fats. So on a very basic level, you can think about it like this. Butter and bacon equal saturated fat. Seed oils equal polyunsaturated fat. Although, in reality, life is always more confusing. But basically, whichever fat you're eating more of, if you don't burn it right away as energy, it'll get stored in your body as that kind of fat. And this means that David and his team could look at the makeup of the butt fat in all of their samples and say,

• 33:40Wendy Zukerman?

  "Well, if you ate a ton of seed oils 15 years ago, are you now more likely to have something like heart disease or to die prematurely?" Which, if Kate's right, should be crystal clear in their data, right?

• 33:58Wendy Zukerman?

  But it wasn't. In fact, having tons of those fats that come in seed oils.

• 34:04Speaker 13

  Was connected to lower risk of dying.

• 34:07Wendy Zukerman?

  Oh, so people lived longer.

• 34:10Speaker 13

  Yeah, if you have more of this in your buttock fat, and if you're a seventy one year old man in Sweden, then you lived longer.

• 34:17Wendy Zukerman?

  Now, it wasn't by much, and one big review paper found that it probably doesn't make too much of a difference to your lifespan if you eat seed oils or not. But bottom line, they're not finding that seed oils are dangerous here. David concluded that having more of these seed oil fats.

• 34:35Speaker 13

  In your buttock fat does not seem to be harmful in any way. It may be the opposite.

• 34:42Wendy Zukerman?

  I talked to Kate about this study.

• 34:44Speaker 01

  Oh, okay. Well, that doesn't make any sense.

• 34:46Wendy Zukerman?

  Wait, when you say doesn't make any sense, what do you mean?

• 34:48Speaker 01

  That's not what I would predict, and you're right, that does contradict my, my theory.

• 34:51Wendy Zukerman?

  It is the opposite of the theory, right? That's the opposite of the seed oil theory. That's suggesting that, yeah.

• 34:58Speaker 01

  Yeah, correct, but it sounds like the opposite. But if you drill down into the details of these studies, which I have done, I usually find that they're missing something very, very important, which makes them misinterpret the finding.

• 35:16Wendy Zukerman?

  Kate took a close look at David's paper, and in an email afterwards, she sent me a few criticisms. One was that she said his study actually did find a link between one of the fats in seed oils and death. But once he adjusted for other risk factors, that link disappeared. I sent these criticisms to David and he wrote back to me saying, among other things, well, you need to adjust for risk factors. These are things like smoking and high blood pressure. And these things can affect your likelihood of getting heart disease or dying. So if you don't control for this stuff, you can come up with the wrong conclusion and say blame these fats for something that smoking is doing.

• 36:01Wendy Zukerman?

  And zooming out, there are other kinds of studies that don't use fridges full of buttock fat, and God help me, I'll say buttock as many times as I like. And in these studies, you can find a couple that suggest seed oils up your risk of heart disease, but the vast majority of the research here doesn't. And in fact, one review looking at almost 50 randomized control trials involving more than 24,000 people, found that on average, these oils are probably good for your heart. And that generally speaking, swapping out saturated fat for seed oils, you know, completely

• 36:43Wendy Zukerman?

  contrary to Kate's advice, is actually the healthier thing to do. Here's how Jason sees it, you know, our butter researcher.

• 36:52Speaker 08

  Replacement of saturated fat with the polyunsaturated fat does reduce the risk of carotid acid disease.

• 36:57Wendy Zukerman?

  The exact opposite of what this trend is suggesting.

• 37:00Speaker 08

  Yeah, so the evidence are pretty consistent.

• 37:03Wendy Zukerman?

  Really, so eating these even like highly refined chemicals, as chemically cannola as you can get, eating those instead of saturated fat, you were actually seeing better health outcome.

• 37:18Speaker 08

  Absolutely.

• 37:19Wendy Zukerman?

  I asked Kate about the science on this.

• 37:21Speaker 01

  I have looked at these studies and I have found a flaw in all of them. After the first, I don't know, 300 studies, I kind of lost interest in, you know, what is the latest way that they're misinterpreting it, you know?

• 37:38Wendy Zukerman?

  If the seed oils theory was as strong as perhaps you'd like it to be, you would expect all these studies, even with their flaws, would find that people who have seed oils, that have polyunsaturated fats in their fat, in their blood, are doing worse. Like even despite the flaws in the studies, right? You would expect.

• 38:01Speaker 01

  I think you do find that. When I look, I do find that.

• 38:05Wendy Zukerman?

  Right. I mean, oh, interesting, because the researchers who did the studies are telling me, like, the ones who did, the ones who were getting the fat samples and making the muffins and crunching the numbers, they're telling me they still think polyunsaturated fats and these oils are the healthier ones. That's when they look at the data, that's what they say.

• 38:26Speaker 01

  It's too large of a leap to make all in one study, right? You can't.

• 38:30Wendy Zukerman?

  But even when they look at the picture, they look at all these different, the muffin, the fat samples, the blood samples, there's so many others.

• 38:38Speaker 01

  Even just one study, it did not convince me, right? It took me many, many, many studies, and it took me knowing biochemistry to become convinced. So a researcher who's doing one study on seed oils in many other studies that they've done, it's a small part of their brain devoted to it. Really, what's needed for any paradigm shift is a wholesale restructuring of the way we approach a problem, right? I mean, paradigm shifts are difficult.

• 39:14Wendy Zukerman?

  Going back and forth with Kate on this, I think it's just that she trusts the few studies out there showing that seed oils are harmful and doesn't trust the many, many studies that show that these oils are fine for you and possibly even healthier.

• 39:33Speaker 01

  I would talk to my patients and ask them, if somebody came out of the hospital, what did you eat before you went into the hospital? Fish. What'd you fry it in? Canola oil. You know, time and time again, I heard things like that. James Gandolfini, what was his last meal? Do you know?

• 39:51Wendy Zukerman?

  I'm not familiar.

• 39:53Speaker 01

  He had shrimp deep fried, a double serving of it dipped in mayonnaise, which is made out of seed oils. That was, he had like two portions of that. That's like the worst form of seed oil. He had a heart attack that night and died.

• 40:06Wendy Zukerman?

  Right. And you think that's what killed him?

• 40:08Speaker 01

  No, it was a lifetime of seed oils, and that was the fatal blow, right?

• 40:12Wendy Zukerman?

  So, that's where Kate stands.

• 40:17Wendy Zukerman?

  But there is one final point to make here.

• 40:21Wendy Zukerman?

  Even though, on the average, the research tells us that the fats in seed oils are healthier, they're not so healthy that if you're eating a diet full of junk food that happens to have seed oils in it, like chips and tater tots and fast food, that that diet will be good for you. So you know, if you go on this new seed oil diet and you bin your seed oils and end up eating a bunch more fruit and veggies and home-cooked meals, you could end up on top. But it probably wasn't avoiding the seed oils that did it. They're more like an innocent bystander here.

• 41:04Wendy Zukerman?

  And so, when it comes to this idea that seed oils are the devil and saturated fat is our saviour, well, perhaps let's give David Shade, our cholesterol researcher, the final word here.

• 41:18Speaker 10

  You know, every, every year, there are crazy diets that people put out without any scientific justification. And that's one of them. It's all crapola.

• 41:28Wendy Zukerman?

  Crapola is how you say crapola?

• 41:30Speaker 10

  Well, it is. Crapola, yeah, that's what it is. That's a technical term.

• 41:35Wendy Zukerman?

  That's Science vs.

• 41:42Speaker 15

  Hey Wendy.

• 41:43Wendy Zukerman?

  Hey, Joel Wendy, supervising producer at Science vs.

• 41:47Speaker 15

  Are you excited that seed oils is now, we've finished the episode, that's it, episode's up?

• 41:51Wendy Zukerman?

  That's right. Congratulations to the audience.

• 41:53Speaker 15

  So how many, how many citations were there in the episode today?

• 41:57Wendy Zukerman?

  There were a hundred and two citations, yes.

• 42:03Speaker 15

  And how can people find these citations?

• 42:06Wendy Zukerman?

  I'm just like looking at them now and my head is spinning, even though I'm the one that put the vast majority of them in there. If people want to see these citations and read more about anything that we talked about today, then head to our show notes and click on the link to the transcript and you'll see like all the citations to basically every word that came out of my mouth today. And we have a podcast recommendation for you. It is called Heavyweight. It's not a new podcast, but they have a new season out and this podcast is phenomenal, right?

• 42:42Speaker 15

  Heavyweight's like, I don't know, I feel like it's the podcast that podcasters rave about, like people who make podcasts notoriously don't have time to listen as much as they want to and you know, we're too busy kind of making the thing to listen to the thing. But Heavyweight is the one show that everyone I know who works in audio never misses an episode of, it's an absolute classic.

• 43:06Wendy Zukerman?

  Yeah, yeah, so go check it out, Heavyweight. It's available on all of your podcast catchers, just like we are. So yeah, so go enjoy it. New season, it's gonna make you laugh and cry and do both at the same time.

• 43:22Wendy Zukerman?

  All right, thanks, Joel.

• 43:23Speaker 15

  Thanks, Wendy, bye.

• 43:29Wendy Zukerman?

  This episode was produced by me, Wendy Zukerman, with help from Joel Werner, Rose Rimler, Nick Delrose and Michelle Dang. We're edited by Blythe Terrell. Fact checking by Carmen Drahl. Mix and sound design by Boomi Hidaka. Music written by Bobby Lord, Emma Munger, Peter Leonard and Boomi Hidaka. Thank you to all of the researchers that I spoke to. I really went back and forth with a bunch of researchers and I just so much appreciate your time and explaining the science to me. So thank you to everyone I spoke to, including Dr. Lorena Pacheco, Dr. Chi San, Dr. Tetsumori Yamashima, Dr. Idris Mughal, Professor Rashika Ahmed, Dr. Atem Talima, Dr. Heidi Silver, Professor Ronald Kraus, Dr. Yu-Tang Wang, Dr. David Sullivan, Professor Peter Clifton, Dr.

• 44:14Wendy Zukerman?

  Lee Hooper and others. A big thank you to Morgan Ruckel, Jen Mortimer, who put me on this whole seed oils adventure. Thank you, Jen. The Zukerman family and Joseph Lavelle Wilson. Science vs. is a Spotify Studios original. You can listen to us for free on Spotify or wherever you get your podcasts. You can find us everywhere. If you are listening on Spotify, follow us and tap the bell icon for episode notifications. And if you like the show, give us a five star review. Come on, do it. And plus, if you want to come say hello, I am on TikTok. So I'm at Wendy Zukerman, W E N D Y Z U K E R M A N.

• 44:56Wendy Zukerman?

  We're also on Instagram, science underscore V S. I'm Wendy Zukerman. Back to you next time.

• 45:10Speaker 12

  From the creators of Zootopia and Frozen comes Disney's Hext. Welcome to Hext and enter the world of witches, where it was foretold that an ordinary girl would become an extraordinary witch and save the world of magic. Disney's Hext arrives in theaters this Thanksgiving.

• 45:30Speaker 16

  What's the secret to being a great host this season? Keeping things deliciously simple, like mixing Simply Cranberry into a festive drink as guests arrive, or serving up a warm mug of Simply Apple on a chilly night. That means less time behind the scenes and more time in the moment with everyone. Crafted with real fruit, Simply juices and fruit drinks make any holiday drink effortless, inviting, and completely delicious. Simply, say yes to simple.