In short
Whether “seed oils” (a popular wellness target) are harmful, and how to evaluate claims about processing, inflammation, obesity/diabetes, omega-6/omega-3 ratios, and frying-related trans fats.
Guests
Emily Oster (economist and data expert) and Perry Wilson (medical doctor). No other guests appear in the episode content provided.
Key claims addressed
- “Seed oils are bad” depends on comparison (seed oil vs what; whole diet vs single ingredient).
- Processing claims: hexane is used as a solvent in extraction, but residual amounts are tiny; other scary-sounding steps in influencer clips are misrepresented (e.g., sodium hydroxide described as carcinogenic).
- Inflammation claim: linoleic acid → arachidonic acid → inflammatory mediators is mechanistically plausible, but randomized trials show no increase in common inflammation markers (e.g., CRP, IL-6, TNF-alpha).
- Obesity/diabetes claim: “linoleic acid is the number one cause” is rejected; observational data points the opposite direction (higher linoleic acid intake associated with lower risk/weight).
- Omega-6/omega-3 ratio: UK Biobank (measured blood levels) shows both omega-6 and omega-3 inversely associated with mortality; the ratio effect likely reflects diet quality/confounding. If causal, increasing omega-3 would be the fix.
- Frying: high-heat, prolonged commercial frying can generate trans fats from PUFAs; home frying is less likely to matter.
Notable examples
- Influencer “processing” clip mentioning hexane, “degumming,” deodorizing, and carcinogen claims.
- Trans fat history via hydrogenation (margarine/Crisco) as a cautionary parallel.
- Mention of a failed LP(a) cholesterol drug trial in the health news roundup (not seed-oil-related).
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOIntroduction to Seed Oils
0:45 to 0:58
Discussion about seed oils and their origins, including avocado oil.
“You can come in when you're ready, take it for a spin, and buy however works for you.”
Introduction to Seed Oils
1:34 to 3:59
Discussion about seed oils and their origins, including avocado oil.
“Perry, did you know that avocado oil is a seed oil because it comes from the seed of the avocado?”
Health News Roundup Introduction
3:59 to 4:16
Introduction to the health news segment of the episode.
“Harry and I will give the official Smasher Pass, and then we'll get to your question of the week.”
Heart Drug Clinical Trials
5:01 to 6:02
Exploration of the failed heart drug trials and implications for health.
“And I applied to topical steroids like I normally do when I'm in moments of crisis like this.”
Heart Drug Clinical Trials
6:13 to 12:36
Exploration of the failed heart drug trials and implications for health.
“We also get to talk about his family life and playing the weekend chef.”
Health News and Updates
12:36 to 14:01
Discussion about testosterone testing in the military and pig kidney transplants.
“has rescinded their mandatory testosterone screening for troops one day after issuing the formal guidance for the troops to be tested.”
Xenotransplantation Advances
14:01 to 17:21
Explore the exciting developments in pig kidney transplants for humans.
“There are about 450 ,000 people in the United States on dialysis at any given time.”
Introduction to Seed Oils
17:21 to 18:31
Discuss the complexities and controversies surrounding seed oils.
“My question with what you just described, which is totally fascinating, is how realistic is this as a, you know, you said there's 450 ,000 people in dialysis waiting for a kidney.”
Understanding Seed Oils
18:31 to 20:07
Identify the main seed oils and their implications for health.
“I mean, so I think this conversation is so fraught because people have no idea how we got here and they don't even know what question we're asking.”
The Cost of Seed Oils
20:07 to 22:25
Analyze how price influences the use and perception of seed oils.
“I asked you at the top of the episode, like, is an avocado a seed oil?”
Show all 30 chapters
Essential Fatty Acids Explained
22:25 to 23:52
Learn about essential fatty acids and their role in the diet.
“Sometimes the other word for this is lineolic acid.”
Fats and Their Impact
23:52 to 26:05
Delve into the differences between saturated, monounsaturated, and polyunsaturated fats.
“Because people are going to need to know.”
The Trans Fat Backlash
26:05 to 28:01
Explore the history and consequences of trans fats in food production.
“Why does Kate Shanahan hate them so very, very, very much?”
The Backlash Against Processed Foods
28:01 to 28:46
Learn about the origins of the backlash against processed foods and how it relates to current dietary trends.
“But it was, this is one of those cases where yes, like it was the processing that caused the harm and like processed foods are potentially bad in some cases.”
Criticism of Seed Oils and Their Processing
28:47 to 29:16
Explore the common criticisms of seed oils and the implications of their processing methods.
“is moving towards trying to get seed oils out of school lunches and all kinds of other other stuff.”
Analyzing Influencer Claims on Seed Oils
29:17 to 30:57
Delve into a clip from an influencer discussing the dangers of seed oils and evaluate its claims.
“But I think the thing that resonates the most with what we've talked about is the first sort of criticism.”
Debunking Myths About Seed Oil Processing
30:58 to 34:29
Understand the actual processes involved in seed oil production and debunk myths surrounding them.
“You couldn't take the seeds and like squeeze them really hard and drip them into your, it would take a very long time.”
The Complex Nature of Food Processing
34:30 to 35:25
Learn how food processing can be both beneficial and harmful, depending on the context.
“Also, the names are like sodium hydroxide.”
Inflammation and Diet: Sorting Fact from Fiction
35:26 to 36:45
Explore the relationship between diet, inflammation, and the claims made by wellness influencers.
“The second claim that I think we hear all the time beyond the processing is inflammatory.”
Examining Linoleic Acid and Its Effects
36:46 to 39:25
Investigate the claims regarding linoleic acid and its supposed role in obesity and inflammation.
“which is that linoleic acid is a precursor to arachidonic acid, which is another fatty acid.”
Introduction to Seed Oils
42:00 to 42:44
The hosts introduce the topic of linoleic acid and its association with health issues.
“And that's when the anxiety kind of kicked in because I was like, what is happening?”
Introduction to Seed Oils
42:49 to 43:30
The hosts introduce the topic of linoleic acid and its association with health issues.
“We also get to talk about his family life and playing the weekend chef.”
Debunking Linoleic Acid Myths
43:30 to 47:52
A discussion on the misconceptions surrounding linoleic acid and its effects on diabetes and obesity.
“And we're back to talk about, you know, does linoleic acid cause diabetes and obesity?”
Omega-6 to Omega-3 Ratio Analysis
47:52 to 52:12
Exploration of the omega-6 to omega-3 fatty acid ratio and its health implications based on recent studies.
“This is debatable because it's based on dietary reconstructions, not actual measurement, et cetera, et cetera.”
Heating Oils and Health Risks
52:12 to 56:00
The hosts discuss the effects of heating seed oils and the potential formation of trans fats.
“I think there's one real concern though, when it comes to polyunsaturated fatty acids in general, and because seed oils are high in PUFAs, I think we do need to talk about what can happen when you fry with these oils.”
Substituting Seed Oils: A Comparative Analysis
56:00 to 1:06:30
Explore alternatives to seed oils and their health impacts.
“And of course, you could also fry in saturated fat.”
Wellness Hacks for School Season
1:07:15 to 1:08:18
Learn effective strategies to prevent sickness during school season.
“And I applied to topical steroids like I normally do when I'm in moments of crises like this.”
Wellness Hacks for School Season
1:08:30 to 1:10:03
Learn effective strategies to prevent sickness during school season.
“I use honey from the farm and I got my crepe.”
Healthy Immunity Tips for Parents
1:10:03 to 1:11:01
Learn about essential immunity practices like handwashing and sleep for parents.
“Do you take a bunch of crap immunity boosters, Harry, like an idiot?”
Healthy Immunity Tips for Parents
1:13:30 to 1:14:09
Learn about essential immunity practices like handwashing and sleep for parents.
“This is Lauren LaRosa from the latest with Lauren LaRosa, the podcast.”
Transcript
Automatic transcript. May contain errors.0:00Emily Oster:This is an iHeart Podcast. Guaranteed human. Remember the 90s, the golden age of snacks?
0:07Perry Wilson:Simple Mills does. Simple Mills brings back that unmistakable throwback taste with favorites like cheddar pop-ums, mini crunchy chocolate chip cookies, and honey cinnamon sweet thins.
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1:34Perry Wilson:Hi, Perry.
1:35Emily Oster:Hi, Emily.
1:36Perry Wilson:Perry, did you know that avocado oil is a seed oil because it comes from the seed of the avocado?
1:42Emily Oster:Oh, actually, no. And I probably should have because we're doing an episode on seed oils. But I thought I assumed it came because avocado like meat is pretty oily. I thought it just came. I thought you just squeezed the meat. Is meat the right term?
1:57Perry Wilson:It's not the right term. But also, I have another fun fact about avocados. This is a good cocktail party fact for you. Avocado seeds are very large and plants that require being reseeded require animals to eat them and poop them out. That's how plants work. And when avocados first existed in the Mesoamericas, there were these giant animals, like 15 foot tall animal megafauna. They have names like megatherium and they had these giant digestive tracts and they could poop out the whole avocado seeds. They just eat the fruits and poop out the seeds. But then those went extinct like 13 ,000 years ago.
2:36Perry Wilson:And avocados -
2:37Emily Oster:Right around the time that Homo sapiens showed up, just pointing that out.
2:40Perry Wilson:I'm not sure that it was totally our fault, but I think we played a role. And then avocados almost went extinct before people discovered how delicious they were and started cultivating them. That was like 8 ,000 years ago. Oh, amazing.
2:53Emily Oster:Thank you, ancestor humans, for keeping avocados going.
2:57Perry Wilson:We almost have no avocados, but instead we have a lot of avocados. So there you go. And you can make them into seed oil, which is the topic of today.
3:06Emily Oster:I love when a good plan comes together.
3:12Perry Wilson:I'm Emily Oster. I'm an economist and a data expert.
3:16Emily Oster:And I'm Perry Wilson. I'm a medical doctor.
3:18Perry Wilson:It's Thursday, September 10th, 2026. And this is Wellness Actually.
3:22Emily Oster:Because you're getting a staggering amount of health and wellness information nowadays from every source imaginable. And some of it is awesome.
3:30Perry Wilson:And some of it is, well, actually bullshit. Fortunately, we are both people who know how to read studies, how to parse the data, and can tell you what's worth thinking about and what you can safely ignore.
3:44Emily Oster:But before we dig in, a note that this podcast is for educational purposes and should not be construed as medical advice. We don't know your unique situation, so talk to your doctor for personal health decisions.
3:56Perry Wilson:This week we're asking, what's the deal with seed oils? Harry and I will give the official Smasher Pass, and then we'll get to your question of the week. But first, let's do the health news roundup after the break.
4:16Emily Oster:We all miss the 90s, the music, the shows, the outfits, and without a doubt, the snacks.
4:22Perry Wilson:Simple Mills is bringing back the golden age of snacking. They taste delicious like the snacks you grew up with, only they're made with real ingredients like watermelon seed flour, almonds, cashews, flaxseed, and organic coconut sugar. Fancy.
4:37Emily Oster:You'll love the throwback taste of cheddar pop-ums, the nostalgic flavor of mini crunchy chocolate chip cookies, and the familiar crunch of honey cinnamon sweet thins.
4:46Perry Wilson:Available in snack packs that are easy to toss into lunchboxes, backpacks, or your own bag. Simple Mills snack packs are simply the coolest.
4:55Emily Oster:Simple Mills. Throwback taste. Grown-up ingredients.
4:58Perry Wilson:I had a huge body flare-up again. Was itchy from head to toe. And I applied to topical steroids like I normally do when I'm in moments of crisis like this. You know, I normally wait about 30 minutes and I'm like, okay, so this is not working. And so I applied again and waited another 30 minutes. And I'm like, this is not going down. What is going on here? And that's when the anxiety kind of kicked in because I was like, what is happening? My entire world and idea of what it was to manage my eczema at that time completely crashed. That's when I started doing research for the first time. And then I realized, wow, I think the medicine stopped working for me.
5:46Perry Wilson:And my body was just going through maybe a withdrawal process.
5:49Emily Oster:This is Skin Queries. Listen on the iHeartRadio app, Apple Podcasts, or wherever you get the stories that make you feel understood. I'm Martha Stewart from the Martha Stewart Podcast. In this special episode brought to you by McCormick Signature Seasonings, I got to chat with Reddit founder Alexis Ohanian about his new venture, Retrieve Air. We also get to talk about his family life and playing the weekend chef. I'm a simple man. I use honey from the farm and I got my crepe. That's it. The girls like their Nutella. That's my breakfast ritual. I'm usually phoning in lunch a little bit because I'm really planning on a delightful dinner.
6:30Emily Oster:The girls really like steak. I spoil them. So even if I'm doing kebabs, I'm using ribeye, I'm doing it right. Okay, well, please. Listen to the full episode of the Martha Stewart Podcast wherever you get your podcasts.
6:46Perry Wilson:And now for the health news of the week. Perry, there are a bunch of articles about how a promising heart drug has failed in clinical trials. What happened? And is it something we should have predicted?
7:03Emily Oster:I mean, this is actually really has sent a shockwave around the cardiovascular community. So the story here is that cholesterol has many different subtypes. And some of them, like LDL cholesterol, we know are both associated with heart disease, like heart attacks and strokes, and that if you reduce them, then the risk of heart attack and stroke goes down. So that's true of LDL cholesterol. It is causally associated with cardiovascular disease. Therefore, reducing it changes your risk of cardiovascular disease. That's why statins work. There's another subtype of cholesterol called lipoprotein A, sometimes referred to as LP little a.
7:41Emily Oster:And the data is completely unambiguous that people with higher levels of LP little a have a higher risk of heart attack and stroke, just like LDL. It's like, looks very, very similar. But it was really a problem because unlike LDL, which can be influenced by lifestyle factors such as diet, LP little a seemed to be entirely genetically determined. It was just like, you rolled the genetic dice, that's your LP little a, sorry. So obviously the race was on to develop a drug that can reduce LP little a. And Novartis did have one called Pelicarsin. And in phase two trials, when they did randomized trials of this drug versus placebo, people's LP little a went down by 80 % on this drug.
8:27Emily Oster:Slam dunk, reducing this level of a subtype of cholesterol. all. But that doesn't matter, right? What matters is, does taking the drug actually reduce your risk of heart attack and stroke? Not, you know, does it change this surrogate marker? And of course, we all assumed, of course it will, because we know that LP little a is very strongly associated with these outcomes, just like LDL was. And if we can reduce it, we'll reduce the risk of these outcomes. And you probably see where this is going in a phase three trial of 88 ,383 people, all of whom had high LP little a and history of heart disease.
9:01Emily Oster:They were randomized to get this drug, which is a monthly injection versus a placebo injection. And all we know so far is that there's no difference in the subsequent rate of major adverse coronary events, which was the primary outcome of the trial. People were so confident in this. And I'll tell you, this enters the wellness space because a lot of direct-to-consumer testing labs will tell you your LP little a level. They'll be like, Ooh, it's the new hot biomarker of cardiovascular risk. Like a lot of people listening who have done that testing will know what their LP little a is. And it turns out like, does it even matter?
9:40Emily Oster:So, so Emily, like this is sort of your area here, right? We have a clear correlation between a level and an outcome, but changing the level doesn't change the outcome. Yeah.
9:49Perry Wilson:I mean, it's not dissimilar from something like vitamin D, right? Like within the normal range, you know, above 20 people with higher vitamin D measurements, with their blood type have all kinds of better outcomes. And you can change vitamin D by giving people vitamin D supplements. But it turns out that that changing doesn't change any actual outcomes, even though it changes this intermediate marker. And it suggests to us that that marker, probably like this one, maybe is picking up something else. Or certainly that's one explanation that this is a marker of some other aspect of probably genetics in this case, or some other bodily feature.
10:28And so just moving around the marker, okay, but it actually doesn't move
Read the full transcript
10:32Perry Wilson:the underlying thing.
10:34Emily Oster:Yeah. I often think of this as like grip strength, which yeah, clearly people with stronger grip strength have better health outcomes. But if you just took someone and made them train just their grip strength, that doesn't actually do anything, right? It's a proxy. I did look to see like, could this have been predicted? And I checked because you and I often debate about Mendelian randomization as a proxy for causality in an observational world. There have been several Mendelian randomization studies of LP little a, and all of them have had suggested that LP little a was causally linked to major adverse coronary events.
11:11Emily Oster:Now it is always possible that this, that that's still true. And this drug just like maybe increased coronary events through some other process. Although now I'm, you know, I'm having to invoke some special pleading to maintain the LP little a hypothesis.
11:26Perry Wilson:And just to bring a little economics into it, Novartis' stock price went down by 15 % when this came out. So this was a surprise to the stock market as well as a surprise to the people doing the trial, presumably.
11:44Emily Oster:Yep. Back to the drawing board, guys. Okay. Moving on. Another example of the wellness actually curse striking again. By the way, Em, I don't know if you noticed this. We got an email. This is not the news item, but normally the wellness actually curse is a good thing because we mentioned people doing nefarious things in healthcare and then they get fired or whatever, and that's all good. But a month ago, we mentioned Dolly Parton and now I'm worried that this is all our fault.
12:16Perry Wilson:Dolly Parton was such an amazing person. That is not the topic of today, but I think just
12:21Emily Oster:like, wow, what an incredible legacy as a person.
12:25Perry Wilson:So just a note here, Dolly Parton, we could all aspire.
12:30Emily Oster:Absolutely. So we apologize if we had anything to do with that, but let's do take credit for this recent example of the wellness actually curse, which is that the Pentagon has rescinded their mandatory testosterone screening for troops one day after issuing the formal guidance for the troops to be tested. So Emily, what's going on with testosterone in the military?
12:55Perry Wilson:I mean, as we said at the time, it doesn't really make sense to do this. There's a lot of unclear reasoning. It seemed at the initial time, like they were suggesting it for everyone, including women, really didn't make any sense. It then seems like they dialed that back to like men over 30, which still makes more sense, I guess. But then they published a draft and then they took it down. The links on the page say page not found. They didn't even try for a redirect, which I think is really better practice for your website. They've indicated that the guidance has been temporarily rescinded to allow for updates.
13:35Perry Wilson:And that's where they are. So my strong guess is we will never hear anything about this again.
13:42Emily Oster:A bold prediction. I like it. Okay.
13:45Perry Wilson:So there we go. Let's find out. Our last piece of health news is fun. Yeah, it's good news. It's about pig kidneys. So we have hit a record on a pig kidney transplant. You're a kidney doctor. How excited was the kidney community?
14:05Emily Oster:No, we are very excited. There are about 450 ,000 people in the United States on dialysis at any given time. And those are all people with kidney failure. They're committed to dialysis three times a week, all of whom could potentially benefit from a kidney transplant. transplant, but we're woefully inadequate in terms of the supply of human kidneys. There's just not enough to go around. So we have to really make careful decisions about who's eligible and who's not and so on and so forth. Xenotransplantation is the idea of putting another animal's organ into a human. And as you can imagine, this is not easy because animals have different DNA and the immune reactions are going to be stronger.
14:48Emily Oster:But pig kidneys are about the right size for human kidneys. And the science here has advanced really dramatically. So what is happening here is we're not just taking a random pig from the slaughterhouse and grabbing their kidney and sticking it in someone. These are specially genetically engineered pigs. They've been CRISPR cast to remove some of the antigens that a human would respond to in a pig kidney. They're sort of, they've humanized kidneys. They appear more human to our immune system than they otherwise would. They are raised in a completely sterile facility. These facilities are crazy.
15:27Emily Oster:These are germ-free pigs because pigs will have different infectious organisms than humans have. And when you immunosuppress a human, you don't want to give them some weird pig infection that we would otherwise fight off because those things are always terrible. So these pigs are all born by C-sections, so they can't be colonized by their mother's vaginal flora. They are in these sterile environments where people are like wearing full suits of, you know, like biohazard suits. So there's, it's like boy in a bubble pigs, basically. They also edit out, this just has the worst possible acronym. So in all animals' DNA, there are these things called endogenous retroviruses.
16:06Emily Oster:These are viruses that in our ancient ancestral history got into our DNA and sit there and then they get passed on genetically, like from one person to another. And most of them never reactivate, Humans have systems to prevent those endogenous retroviruses that live in our DNA from ever becoming active again. We've evolved to those defense systems. But what we don't have defense systems against is porcine endogenous retroviruses, abbreviation, PERVs. So a major problem with pig xenotransplantation was PERVs because those, although pigs can suppress their own PERVs from coming out, humans cannot keep the pervs from coming out of the pig kidneys.
16:54Emily Oster:These were genetically edited away, the majority of them. And so an amazing bit of science allowed a human to live with a pig kidney for a record 271 days off of dialysis. And then he finally got, this is a guy named Tim Andrews, finally got a human transplant after waiting that amount of time. So this isn't going going to be every single patient on dialysis yet, but the progress has been really tremendous and it's pretty cool.
17:20Perry Wilson:Yep. My question with what you just described, which is totally fascinating, is how realistic is this as a, you know, you said there's 450 ,000 people in dialysis waiting for a kidney. Is this something where like six of them in a year would get a pig kidney? Like it's a cool, interesting thing you could do, but very unlikely to actually be a meaningful thing. Or Or is this one step in the direction of lab-grown kidneys that we could actually replace human kidneys with?
17:51Emily Oster:I think lab-grown kidneys, the progress hasn't been as fast. Growing a kidney from scratch, we can't get that quite right yet. But the pigs are growing the kidneys on their own, and they look like kidneys, and they're the right shape, and they have all the tubes and stuff like that. So I actually think xenotransplantation comes first before lab-grown kidneys. And I mean, I'm not going to say every technological barrier has been overcome, but I actually suspect that we will, like, we're going to be on an upward ramp of this and you're going to hear about a lot more. Amazing. Pretty cool.
18:22Perry Wilson:That's really cool. All right. That's it for the health news of the week. Now, what's the deal with seed oils?
18:30Emily Oster:All right. Seed oils. How did we get here?
18:36Perry Wilson:How did we get here? I don't know. I mean, so I think this conversation is so fraught because people have no idea how we got here and they don't even know what question we're asking. So I would say the way people ask this question is, are seed oils bad? Right. To which I would say, well, relative to what? And that is sort of the whole frame here is like, what are you comparing them to?
19:03Emily Oster:Yeah, we need to cook with fat. And what do you mean by bad? Because if you're not cooking with some form of fat, then you're just not cooking, guys. So yes, seed oil versus.
19:13Perry Wilson:We're going to say this whole episode is going to be seed oil versus or within seed oil versus. And I think that's the right way to ask.
19:21Emily Oster:That means we get to talk about beef tallow, which just was not even in my lexicon until RFK Jr., I guess.
19:28Perry Wilson:For reasons I don't even want to get into this weekend, I was on Amazon looking for something and I came across a product that was a collagen beef tallow face cream. And I was just like, this is all the things. I should buy this and put it on my face. So maybe next time we come, I'll have a beautiful face.
19:51Emily Oster:It sounds like a face with a lot of pimples. I don't know. I feel like beef tallow on your face is not going to keep your pores nice and open, but what do I know?
19:59Perry Wilson:So yes, we will discuss beef tallow as a great alternative or possibly not to seed oils. But the other thing I think people don't understand is like, what is this, right? I asked you at the top of the episode, like, is an avocado a seed oil? Yes, although not everybody thinks that. So there's a hateful eight seed oils. Do you know what they are?
20:22Emily Oster:I do now. this comes from Kate Shanahan and these are the seed oils. So canola oil, also known as rapeseed oil, cottonseed oil, soybean oil, sunflower and safflower oils, grapeseed oil, not rapeseed, but grapeseed oil, corn oil and rice bran. Did I get them all?
20:45Perry Wilson:First of all, I just want to be clear. That's right. This comes from someone whose kind of whole thing is she doesn't like seed oils. Her tagline is that she's standing up to health authorities about seed oils. So she's not a fan.
20:57Emily Oster:Talk about a niche.
20:57Perry Wilson:Some of these things aren't seeds. Okay. Just to be clear, corn is not a seed oil. Rice, anyway, fine. Yeah, sure. It's a grain. Rice is a husk. I don't know. But some of these are seeds. They're seeds.
21:10Emily Oster:Yeah. So, okay. So seed oil is a misnomer, but what they are, but the list is the list, right? And you said avocado is a seed oil, but most people don't put avocado in the seed oil category. So this is a vibe more than anything else, right? Seed oils. It's like the cheap, widely available oils that I can buy in the supermarket or that I'm going to get from a restaurant that's frying stuff.
21:31Perry Wilson:And I think that's the thought actually. It's useful for people to hold for, like, think about this whole thing. It's like most of these oils are cheap. If you ask like, what is distinguishing these? It is not as so much the seeds as the price. And these tend to be the kinds of oils you are using in a lot of processed foods, a lot of packaged foods, because they are cheap. And that's going to come up when we try to evaluate their health impacts because of how price works. Yeah.
21:58Emily Oster:I mean, we've telegraphed multiple times in wellness, actually, how price signaling always confounds health relationships because rich people get better healthcare, at least in the United States. True. All right.
22:13Perry Wilson:So what these things do share, I think, which is consistent with corn oil, safflower oil, et cetera, is that they have a lot of omega-6 polyunsaturated fatty acids. Sometimes the other word for this is lineolic acid. Am I saying that?
22:30Emily Oster:Linoleic acid is the - Linoleic. Yeah. Linoleic acid. Let's do some science. It is one of our essential fatty acids. Yeah. Yeah, yeah. Remember when we were talking about supplements and stuff, we talked about essential vitamins and minerals and things like that. By the nutritional term, essential doesn't mean like, ooh, great, and part of a healthy diet. It means a substance that you need for survival that you can't synthesize yourself. And there are two essential fatty acids, and one is linoleic acid, the major constituent of things like corn oil. If you don't get enough linoleic acid, you die, and you can't make it yourself.
23:09Emily Oster:So you literally like right off the top here, you do need some, you need to get some into your body somehow. I mean, we can argue how much is too much. And I will say that the deficiency states are pretty rare because you don't need a ton of linoleic acid to survive. You just need a little bit. And almost everyone easily gets that through their diet. So we don't see linoleic acid deficiency too much unless people have like various GI symptoms. The other essential fatty acid is known as ALA. It's an omega-3 fatty acid. And I think we've got it. We're going to get there, but is now a good time to talk about polyunsaturated versus monounsaturated versus saturated fats?
23:54Emily Oster:Because people are going to need to know.
23:56Perry Wilson:Let's do it. Go for it. Enjoy yourself.
23:59Emily Oster:Okay. So saturated fat, you've heard that term and probably because for 40 or so years, saturated fat was at the center of the lipid hypothesis, which was the idea that consumption of saturated fats increased cholesterol and promoted cardiovascular disease. This is almost certainly true. What a saturated fat is, what saturated here means is that the chain of carbons, which is part of the lipid structure, has only single bonds, no double bonds. So it is full of single bonds, saturated with single bonds. It actually means there's hydrogen sticking off, but it's fine. Just think all single bonds.
24:41Emily Oster:And the practical upshot of this is that because they're all single bonds, the fatty acids aren't very kinky. They lay very straight, which means they can pack together very tightly. And that means that something that's high in saturated fat is going to be solid at room temperature.
24:57Perry Wilson:Like butter or beef tallow.
24:59Emily Oster:Butter or beef tallow. If you put a double bond in that long chain of carbons, a single double bond, you get a monounsaturated fatty acid. And oleic acid is probably our prototypical one there. That's the major component of olive oil. And by putting a little kink in that chain, they don't pack nicely together as much and you get something that's liquid at room temperature. And then a polyunsaturated fatty acid has multiple double bonds. So multiple little kinks, also going to be liquid at room temperature. And as you pointed out, linoleic acid is a great prototypical PUFA, polyunsaturated fatty acid.
25:38Emily Oster:And now you know the chemistry that explains why beef tallow and butter are solid and olive oil is less so. Although you might note that olive oil, like if you put in your refrigerator, congeals, right? Whereas like, because it's only a monounsaturated fatty acid, but then, you know, sunflower oil won't. I don't know. That's kind of neat. Food science.
25:57Perry Wilson:Food science. So I think it's worth talking about, you know, in some ways, all of the like lead up to this. And if you just talked about this, like you would talk about it in chemistry class, okay, this is a kind of fatty acid. It's something that you need. Without it, you would die. It feels like, all right, cool. Why does Kate Shanahan hate them so very, very, very much? What'd they do to you, Kate Shanahan? And I think, you know, part of, for me, I think a big piece of this answer is trans fats. So people in the 50s and 60s get very, people were like very unhappy, maybe like later than this, about saturated fats and were looking for things like margarine.
26:37Perry Wilson:Remember margarine? Margarine was so good for you. And margarine was full of trans fats. Trans fats turned out to be really bad for you. Trans fats were bad. They did not good. They gave you heart disease.
26:51Emily Oster:Surprise. Pretty clearly. And trans fats are an industrial process. You don't really get trans fats from natural sources. The reason margarine works, and Crisco is maybe the first example of this, is that if you get these plant-based fats, the monounsaturated and polyunsaturated fatty acids, they're liquids. And people didn't want to put liquids on their toast, right? They wanted to spread something on their toast. And so what Crisco, what the good people at Procter & Gamble figured out in 1911, is that they could take cottonseed oil, which was a liquid, and they could hydrogenate it to make those double bonds back into single bonds.
27:31Emily Oster:So they would saturate the unsaturated fat. And that's what hydrogenated vegetable oil or whatever is. That process made Crisco solid and shelf stable, right? So now you've got, instead of a drizzly oil, you've got something you can spread or whatever you want to do with. And margarine was exactly the same. But the process of hydrogenation by breaking those kinks and making them straight again, made trans fats the way it used to be done. They're now banned. And so you can't use those processes anymore. But it was, this is one of those cases where yes, like it was the processing that caused the harm and like processed foods are potentially bad in some cases.
28:13Perry Wilson:So there was this backlash against trans fats. They ended up being banned. And I think part of that was then people got into, okay, like let's processing in all forms is bad. And then, and then And I think that translated to like things that are not butter are bad because margarine was a substitute for butter. And so shouldn't we just go back to butter? And that has led us to our current moment where the flipped food pyramid now has beef tallow and butter at the top and other things not at the at the top. And actually, RFK Jr. is moving towards trying to get seed oils out of school lunches and all kinds of other other stuff.
28:54Perry Wilson:So it's like, you know, the trans fats were bad, but that is different from saying that you shouldn't have canola oil.
29:02Emily Oster:Right, right, right. Yeah, they were taking seed oils, they were messing them up and creating something bad that has now been banned. And now we're saying, oh, therefore seed oils are bad. And we need to evaluate those claims based on what seed oils are today. So let's do that. But I think the thing that resonates the most with what we've talked about is the first sort of criticism. And there are a number of criticisms of seed oils. But I think the first criticism is the it's how they're made problem, right? The processing. So can I play you a clip of a typical influencer on Instagram talking about the processing of seed oils?
29:43Emily Oster:Yes. What are the most harmful foods that people constantly eat? no question it's seed oils. The reason for this is that it's not the plant, okay? It's the distance from the plant to the table. When you put a canola plant or a rapeseed, same thing, into a commercial press, it comes out gummy and you degum it with hexane, which is a known neurotoxin. Then you take that neurotoxin degummed oil and you heat it to 405 degrees and you turn it rancid. So it's putrefied and now it smells and you need to deodorize it with sodium hydroxide, which is a very powerful carcinogen. And then you sometimes bleach it before you bottle it and put it on the shelf.
30:15Emily Oster:You ever notice when you go down the shelf, the aisle in a shelf in a grocery store, it's all the vegetable oils, Wesson oil, vegetable oils. They're all exactly the same color, that beautiful, perfect yellow color. That would never happen. If you pressed a thousand plants and turned it into oil, you would not get that level of consistency. That's chemically induced. And then they put a heart healthy label on it. These are pro-inflammatory that cause a massive amount of inflammation in the body. So Emily, this clip has multiple claims, all very scary. And I actually think because these get repeated over and over and over again, I think it's just worth like going through them once, talking about the processing.
30:52Emily Oster:Yes, these are like, you can't just like squeeze a seed as hard as you can. Actually, there's cold pressed seeds. You just wouldn't be very much.
31:01Perry Wilson:You couldn't take the seeds and like squeeze them really hard and drip them into your, it would take a very long time.
31:06Emily Oster:Yeah. But there are companies that are doing cold-pressed seed oils. But in any case, the standard way that your canola oil is getting done is a process thing. So let's walk through it. And I think basically the only thing true that was said in that clip is that hexane is used as a solvent here, right?
31:24Perry Wilson:That sounds right. Yeah. I mean, he did list some seed oils. That seemed right.
31:27Emily Oster:Yeah. So this is true. Oils don't dissolve in water. So if you're trying to extract them from something, you need a non-polar solvent. Remember chemistry like dissolves like. So, and hexane is what is typically used. So that extracts the oil. Then the hexane is distilled off. There is potentially some residual hexane in seed oils. The limit is less than one part per million, you know, and then this is just the standard like influencer thing is like, I'm going to take this true fact. There's some processing here. And then I'm just going to extrapolate to everything else. So for example, hexane is, oh, it's a known neurotoxin.
32:12Perry Wilson:At some doses, yeah.
32:14Emily Oster:Yeah, yeah, yeah. If you're sniffing glue, it's a neurotoxin. If you fall into a vat of hexane in a hexane factory, it's a neurotoxin. That's true. But the dose makes the poison, right? like tiny amounts of stuff your body deals with. You get exposed to all the time through multiple sources. I'm sure you're getting a lot more pexane filling up the gas in your car than you are from your canola oil.
32:39Perry Wilson:This is such a classic wellness influencer tactic online and really in all of, in a huge share of the panic headlines that I deal with, it is just this point that people are saying, well, there's a tiny amount of this thing in something. And if you like ate that thing as your primary food, it could cause a problem. It's like, yeah, I get it. Or we fed mice this thing as their entire diet. And that wasn't good for them. It's like, that's actually different than there's a teeny, teeny weeny amount of it. And those are just not the same. And that's it. They're just not the same.
33:11Emily Oster:Yeah. The world is, even natural foods, the world is full of toxins and poisons. Like we have multiple systems in our bodies. Sorry, guys.
33:16Perry Wilson:That's why you have kidneys and a liver. Exactly. Okay. That's what they're doing.
33:19Emily Oster:It's their whole fucking job. Just the way it is. A couple of other errors there. Sodium hydroxide is a powerful carcinogen. That's not true at all. Sodium hydroxide is just a base. We add it to the water supply in areas where the pH of the water is too low. The water is too acidic, so you add sodium hydroxide to increase the pH to a normal level of seven or so. So what you're saying is the water is a carcinogen. Is that what I'm hearing? I just like at least hexane, you can be like, yeah, I guess if you sniff a bunch of glue, it's bad for you. But like sodium hydroxide, it's just a base. I don't know what that is.
33:59Emily Oster:And the other thing that the oil is like made rancid by the processing or denatured, that's just also not true. It is extracted under some heat and we will go through what can happen with prolonged frying of oil at extremely high temperatures. That's not what's being used here. So again, just influencers saying stuff that's scary because saying scary stuff gets you to share with your friend and be like, oh, look, this is scary. Maybe we shouldn't use canola oil anymore.
34:30Perry Wilson:Also, the names are like sodium hydroxide. Oh, yes, that doesn't sound good. But what about sodium chloride? How does that sound? That's scary. That sounds scary. That's salt.
34:45Emily Oster:Yeah. Yeah. This is all sort of the processing is bad. And processing is really neither good nor bad. Processing can create bad things like super sugary, easily digestible food that gives us too many calories and makes us fat. Absolutely. But processing in and of itself is not a poison. Yeah.
35:11Perry Wilson:I think this is like a sort of legacy of this is legacy in this case of the trans fat stuff. It's also a general legacy of this idea of ultra processing and processing itself as the problem as opposed to what it is processed into that is more of the of the issue. All right. The second claim that I think we hear all the time beyond the processing is inflammatory. Boy, does a wellness influencer love inflammatory.
35:35Emily Oster:I mean, good Lord. Where would we be without inflammation?
35:36Perry Wilson:People would be more excited about being inflamed or not inflamed or like, I'm not even sure if I would know if I was inflamed, but I, for sure, it's problematic.
35:43Emily Oster:That sounds like something an inflamed person would say. It definitely does.
35:47Perry Wilson:I'm pretty sure. I'm pretty, consumed a lot of sodium something yesterday. And So is this, first of all, what does that mean?
35:58Emily Oster:Do we know?
36:00Perry Wilson:Do we have a sense?
36:02Emily Oster:Yeah, I think I know. Okay. So inflammation is the process of your immune system doing something. You know, it literally comes from like redditing up, right? Like you get an injury and it turns red. It's inflamed. There is an increasing recognition that inflammatory molecules, things like C-reactive protein, are different levels in different people, and that those levels might be dictated by some underlying pathology, chronic inflammation, and that chronic inflammation isn't good for you. And so a lot of times they're using these blood proxies of inflammation, often CRP. And let me give you an argument that you'll see from the influencers about linoleic acid, which is that linoleic acid is a precursor to arachidonic acid, which is another fatty acid.
36:53Emily Oster:This is another thing your body needs. It transforms linoleic acid and essential fatty acid into arachidonic acid. And downstream of arachidonic acid are a bunch of inflammatory molecules. In fact, inhibiting arachidonic acid is some of the stuff that like NSAIDs do, things downstream of arachidonic acid is some of the stuff that NSAIDs do to reduce inflammation. So it's like, well, it's on the pathway that generates inflammatory molecules. Therefore, it must itself be inflammatory. True? False?
37:25Perry Wilson:Interesting and a plausible hypothesis, which needs to be tested in randomized trials. This is a classic example of like, here's an interesting mechanism. Could this be something that was true? How would you know? Well, you would randomize people to higher or lower levels, and you would see what happens to their C-reactive protein or some other measure, but that would be the classic measure. And that would tell you whether this downstream path is actually having implications for, you know, what is realized in people. And they have done that. And the answer is no, that actually higher intakes do not correlate with higher metrics of inflammation or on many, many different versions of inflammation measures.
38:11Emily Oster:Yeah. A nice systematic review in the Journal of the Academy of Nutrition and Dietetics in 2012 looked at 15 randomized trials, which randomized people to higher linoleic acid intake versus other fats. And not a single one showed an increased C-reactive protein in the high linoleic acid group. There's also no effect on IL-6, TNF-alpha, ICAM-1, LMP selectin, fibrinogen, platelet activity, or any of the measured prostaglandins, or thromboxane. So if you have a favorite inflammatory marker -
38:44Perry Wilson:Thromboxane did cause me concern.
38:45Emily Oster:I know you're a big thromboxane person.
38:47Perry Wilson:And I'm, you know, I mean, I think in some ways this is like great science. I think we should give some credit to this, which is like, this is how science should work. People say, okay, here is a thing that could be true mechanistically. Maybe we have some evidence in mice. Maybe we have some evidence in vitro. Let's go test this in people to see if it is important and it happens inside people. You test it and then you learn something. That's how science works and that's really cool. But once you get the answer in people, then you don't go back to the other thing and say, oh, well, because of this hypothesis I had.
39:19Perry Wilson:Well, no, you did the hypothesis. You did the testing and then you said, no, that's it. We're done with that.
39:23Emily Oster:Yeah, move on.
39:25Perry Wilson:Yeah, move on. Let's move on to issue three.
39:27Emily Oster:Oh, I love issue three. Issue three. Okay. Can we play this? We're going to let someone else, we're going to let a wellness influencer introduce issue three here. I believe that the number one cause of obesity and diabetes in humans is excess linoleic acid in the diet. Linoleic acid is an omega-6 polyunsaturated fatty acid found in high amounts in seed oils. Excess amounts of this fatty acid break down into compounds that make you want to eat more, causing weight gain. Excess linoleic acid also causes inflammation in the human body by raising oxidized LDL and Lp little a. Here's how much linoleic acid is in these fat sources.
40:08Emily Oster:Tallow, low, 2%. Ghee, 2%. Butter, 2%. Avocado oil, 14%. Olive oil, 15%. Canola oil, 25%. soybean oil, 55%, corn oil, 60%. Animal fats are clearly the best. If you want to lose weight and be healthy, get the lowest amount of linoleic acid in your diet as possible. That is insane to say that the number one cause - Number one, number one cause. Number one of diabetes and obesity is excess linoleic acid. like it's the most specific. Are you familiar with snack foods, my friend? The number one cause diabetes and obesity in this country is excess linoleic acid. Emily, let's take a break and we will unpack that one in a moment.
41:06Perry Wilson:Is it number one or number two after the break?
41:11Emily Oster:Remember the 90s, the golden age of snacks? Simple Mills does.
41:14Perry Wilson:Simple Mills brings back that unmistakable throwback taste with favorites like cheddar pop-ums, mini crunchy chocolate chip cookies, and honey cinnamon sweet thins.
41:23Emily Oster:Only now, they're made with thoughtfully chosen ingredients like watermelon seed flour, cashews, flaxseed, and organic coconut sugar.
41:30Perry Wilson:Available in snack packs that your inner 90s kid would have begged for. With ingredients your grown-up self can appreciate.
41:37Emily Oster:Simple Mills. Throwback taste? Grown-up ingredients.
41:40Perry Wilson:I had a huge body flare-up again. was itchy from head to toe. And I applied to topical steroids like I normally do when I'm in moments of crises like this. You know, I normally wait about 30 minutes and I'm like, okay, so this is not working. And so I applied again and waited another 30 minutes. And I'm like, this is not going down. What is going on here? And that's when the anxiety kind of kicked in because I was like, what is happening? My entire world and idea of what it was to manage my eczema at that time completely crashed. That's when I started doing research for the first time. And then I realized, wow, I think the medicine stopped working for me.
42:28Perry Wilson:And my body was just going through maybe a withdrawal process.
42:31Emily Oster:This is Skin Queries. Listen on the iHeartRadio app, Apple Podcasts, or wherever you get the stories that make you feel understood. I'm Martha Stewart from the Martha Stewart Podcast. In this special episode brought to you by McCormick Signature Seasonings, I got to chat with Reddit founder Alexis Ohanian about his new venture, Retrieve Air. We also get to talk about his family life and playing the weekend chef. I'm a simple man. I use honey from the farm and I got my crepe. That's it. The girls like their Nutella. That's my breakfast ritual. I'm usually phoning in lunch a little bit because I'm really planning on a delightful dinner.
43:12Emily Oster:The girls really like steak. I spoil them. So even if I'm doing kebabs, I'm using ribeye, I'm doing it right. Okay, well, please. Listen to the full episode of the Martha Stewart Podcast wherever you get your podcasts.
43:29All right.
43:30Emily Oster:And we're back to talk about, you know, does linoleic acid cause diabetes and obesity? And is it, in fact, the number one cause of diabetes and obesity? Okay.
43:44Perry Wilson:So this is a place where actually it will be really, really quite important to think about relative to what and think about what the evidence says. because in fact, because there is a lot of linoleic acid in a lot of processed foods, you can sometimes get, and we'll sort of get into this, but you can get correlations in these spaces. And so we really want to like, actually, we want to look at the evidence. Yeah. Your Twinkie has some linoleic acid in it.
44:19Emily Oster:It may not be the linoleic acid. It may just be the Twinkie.
44:22Perry Wilson:It's the Twinkie. The other things in the Twinkie. So here there is a little bit of potential mechanistic evidence. There's like mouse study where more linear leg acid exposure raises their food intake. So there's like a little bit of mouse evidence, but the people evidence kind of goes in the other direction. Yeah.
44:46Emily Oster:Yeah. The mouse evidence suggests that there's an endocannabinoid effect of linoleic acid. So you'll hear the cannabinoid. That's the same thing that marijuana does, like gives you the munchies. There's some receptors in your brain that make you hungry. And so, yeah, you can get a mouse to eat a little bit more if you really restrict it to a linoleic acid diet. Although, you know, I think marijuana probably has more of an effect on diabetes and obesity in this country than linoleic acid. Actually, the number one.
45:20Perry Wilson:So most it's number two.
45:22Emily Oster:It'd be number two. But you're right. I mean, the observational data clearly shows that higher linoleic acid intake is associated with a lower risk of diabetes and body weight because it's a plant-based oil. You're eating more plants. Right. Yes.
46:13Emily Oster:increases food intake or weight or risk of diabetes and far from being the number one cause.
46:19Perry Wilson:I mean, I think to believe this, forget about the number one cause, to believe this even directionally, you have to think that the biases and the observational data go very strongly in the other direction, right? That somehow the people who are consuming a lot of linoleic acid are really positively selected on other things. And that's like kind of canceling out this effect in the observational data. I didn't have to be quite large in the other direction. So I think that's what you'd have to think, even to have this move in that way, nevermind for it to be important. And yeah, I mean, obviously that claim is just like totally bananas and weird.
47:02Emily Oster:All right.
47:03Perry Wilson:So you know what gets people to click on your thing? If you're just like linoleic acid, It is possibly the 437th tiny contributor to America. So I was like, that's boring. That's a boring reel.
47:15Emily Oster:I'm already bored. But guys, did you know that linoleic acid is the number one cause of sperm count loss in men? Can we just cut that clip?
47:27Perry Wilson:And low testosterone.
47:28Emily Oster:We should do an experiment. We should just cut that clip and put it on Instagram and compare it to a nuanced discussion of - The kidneys.
47:36Perry Wilson:The kidneys. It's like here's what Barry has to say about the - Chance gets more clicks.
47:39Emily Oster:All right. Let's move on to sort of the fourth big claim you'll hear about seed oils, which has to do with the omega-6 to omega-3 fatty acid ratio. So the background here is, I think where this comes about is that historically, like paleo diet world in the olden days, there is some data that we ate a fairly balanced ratio of omega-6 fatty acids versus omega-3 fatty acids. This is debatable because it's based on dietary reconstructions, not actual measurement, et cetera, et cetera. But we probably nowadays in our modern diet do have a higher ratio of omega-6 to omega-3. And what the influencers will kind of spin this as is omega-6 is the angry one that's going to make you inflamed and bad and everything in, and omega-3 is the calm yang to the raging yin of omega-6 or something like that, right?
48:41Emily Oster:And we're all out of whack. The study that gets cited every single time they talk about this ratio is a UK Biobank study from eLife in 2024, 85 ,000 people. And they actually measured the plasma levels of omega-6 and omega-3 fatty acids in people. That's a nice design. So it wasn't like dietary recall. They actually measured it, which is great. And of course, measurement is because these are essential fatty acids, you can't make them yourself. So measurement actually does reflect kind of like what you're taking in. So I actually really like that design. They looked at the ratio of omega-6 to omega-3 and in the highest versus the lowest quintile, so the highest fifth of people in the ratio versus the lowest fifth, the highest fifth had 26 % higher all-cause mortality and 31 % higher cardiovascular disease mortality.
49:33Emily Oster:So that's what you hear. You're like, oh, this ratio is terrible. And the seed oils are giving us all this omega-6. And then people actually read the study. And Emily, if you read the study, instead of just talking about the abstract, what do you learn about how horrible omega-6 is?
49:53Perry Wilson:What you learn is that both of these fatty acids are inversely associated with all-cause mortality, cancer, and cardiovascular disease mortality. It is just that omega-3s are more strongly associated than omega-6s. So both are better than other fat forms, saturated fat in particular, in this study.
50:14Emily Oster:Yeah. So to just say it again, the people who had the highest level of omega-6 in their blood did better than the people with the lowest level. The people with the highest level of omega-3 in their blood did better than people with the lowest level. It's only when you divide the omega-6 by the omega-3 that you get this sort of weird relationship.
50:35Perry Wilson:But this all makes an unbelievable amount of sense if your view is that this is all measuring something else. So when I look at this data, what I see is that these fat metrics, saturated fat, omega-6, omega-3 are all measuring diet quality. And the people who are consuming a lot of saturated fats off on average, a sort of worse diet quality. You see this everywhere in any food frequency diet thing. Anything you see, you see people are consuming a lot more fat, typically also a lot more sugar, generally a lot more calories. That tends to be a group with higher rates of obesity, less exercise, et cetera, et cetera.
51:17Perry Wilson:The people were eating more omega-3s kind of somewhere in the middle. This comes in a lot of snack foods. And so they're going to have a kind of intermediate diet. The people were eating a lot of omega-3s have the healthiest diet. And so what we're measuring here is some sort of overall health in the fear diet and probably also many other things about your behavior and resources and income and education level and so on. And so that's what you're picking up in the data more so, I think, than you're picking up any of these things. But as you said, even if you wanted to take this and say, like, these are all causal, the people who have more omega-6s do better than people with less.
51:55Perry Wilson:That's the kind of basic fact.
51:57Emily Oster:Right. Right. And if you really are worried about this ratio, if you do think it's causal, then the solution would not be to reduce your omega-6. It would be to increase your omega-3, right? Sure. So eat your salmon, folks. This is the fatty fish answer. Yeah, you know who eats salmon?
52:13Perry Wilson:Rich people. Okay. Just to not put too fine a point on it.
52:19Emily Oster:I think there's one real concern though, when it comes to polyunsaturated fatty acids in general, and because seed oils are high in PUFAs, I think we do need to talk about what can happen when you fry with these oils. Don't you think?
52:36Perry Wilson:Yeah. I think we do have to talk about frying. Okay.
52:39Emily Oster:So I'll do the chemistry here. And that is that when you... Remember there are these double bonds in polyunsaturated fatty acids. And when you heat them up really hot, and we're not talking like sauteing in your pan, we're talking 175 to 190 degrees Celsius, like deep fat frying, those double bonds can break. And when they reform, they may reform in the cis position, the nice sort of straight position, like a saturated fat would have, or they might reform in the trans position, and then it's a trans fat. So it is possible to convert a polyunsaturated fatty acid to a trans fat, not just if you're Procter & Gamble, but if you leave it on the stove for hours and hours and hours.
53:26Emily Oster:And we know that trans fats causally increase cardiovascular disease risk.
53:33Perry Wilson:Yes. So I think that that is true. And then I think it's really important to help people like kind of back down from how should you think about that in the world. So this is most important in the commercial fryer space. So if you are commercially frying things at a restaurant, they tend to hold the oil at some temperature for like a long time, many hours, could be days, they're topping it up continuously, and it's like degrading. That is treating these oils in a way that can lead them to have some trans fats. When you are doing this at home, on the kind of scale that most people are frying, even for deep frying, even if you're like raising it to 375 and making some delicious double cooked French fries in your fryer, that is still really not enough time for this to be a meaningful thing.
54:28Perry Wilson:And certainly like sauteing anything in some canola oil, that's just like unrelated to this. It's not getting hot enough for this to matter.
54:37Emily Oster:Yeah, exactly. It really comes from reusing and reheating these oils at high temperatures. And there's data here, rats fed sequentially reheated oil. So they took some polyunsaturated fatty acid oil and they heated it once and fed rats and then they heated it twice and fed rats. So the idea being it's getting successively more degraded by frying. They did show a dose response effect in terms of vascular inflammation. So, you know, this is true. I mean, we also know observationally that humans who eat more fried food have a higher risk of cardiovascular disease. Like, can I really blame the deep fat fryer versus just the fact that you're eating a lot of, you know, fried chicken?
55:23Emily Oster:That's a harder one to untangle.
55:25Perry Wilson:I mean, I think that these, Probably the accurate thing to say about this is that this is mechanistically plausible, and we have other evidence to suggest that there could be some small impacts, but relative to other things you are doing, these impacts are likely very, very small.
55:42Emily Oster:Yeah. The more unsaturated your fat is, the more problematic this is. And so a monounsaturated fatty acid like oleic acid doesn't have as much of this issue, but of course, olive oil is not good for deep frying. The smoke point is too low. But there is high oleic acid sunflower and safflower oils. Those are technically seed oils, but if you're going to be deep frying at home and you are worried about this, those high oleic acid oils that have a high smoke point actually work pretty nicely and put a lot of that to bed. And of course, you could also fry in saturated fat. You could fry in beef tallow.
56:19Emily Oster:And because it's saturated, it doesn't run that risk of forming trans fats with extended heating.
56:26Perry Wilson:Right. Okay. So at the top, I said, I think the right frame for this episode is to ask what you could compare this to. And so I think it's reasonable to ask the question about like substitution here. So let's say you decided, you know, despite having listened so carefully to our episode that you are a seed oil hater and you don't want to consume any seed oils. Like is what, what could you do about that? what would you substitute to? And so it's worth asking the, like, what does the data say about the different substitutions? There are kind of four things people would swap in here. Beef tallow, butter, olive oil, and avocado oil.
57:05Perry Wilson:So can we talk about those?
57:07Emily Oster:Yeah, it's going to make me hungry. But let's run through them quickly. So beef tallow, because it's definitely like having a moment, the Google trends for beef tallow is going up like crazy. I actually think in fact, Whole Foods identified tallow foods as like their number one food trend of 2026. So beef tallow is having a moment. What is beef tallow? So it's fat, it's congealed beef fat. It's about 50 % saturated fat, 42 % monounsaturated fatty acids, and just 4 % PUFA. In fact, the most abundant fatty acid in beef tallow is oleic acid, the same as olive oil, but it's also 26 % palmitic acid, which we do know causally increases LDL.
57:51Emily Oster:It's like that lipid hypothesis way back in the fifties to seventies, that saturated fat increases cholesterol, which causes cardiovascular disease. True. That being said, we do have ways to reduce your LDL now pharmacologically that we didn't have in the fifties to seventies. This is my dad's philosophy. He's like, he's like, I can eat all the red meat I want because I can take my Lipitor and keep my LDL down. And I don't know, maybe there's some truth in that. We know from several studies that, from substitution studies, that beef tallow, substituting beef tallow for other seed oils increases LDL, but there's no outcome trials.
58:30Emily Oster:So I can tell your LDL will be a little higher if you swap in beef tallow, but I can't know for sure whether you're going to have more heart attacks.
58:38Perry Wilson:Butter, similarly, very high in saturated fat, even higher than beef tallow. It is delicious. but it does also raise your cholesterol for the same reasons.
58:49Emily Oster:Yeah. I was surprised looking at the constituents. Beef tallow seems maybe a little healthier than butter.
58:55Perry Wilson:Stop it. That's enough out of you. But yes, perhaps. But butter is so delicious. And I think that's worth saying. It is delicious. And all foods can be sometimes food. And butter is It's delicious. All right. So olive oil, I will say, is predominantly oleic acid, which is omega-9, actually, not omega-3, right? It has omega-3.
59:19Emily Oster:Yeah, omega-3, you need fish stuff.
59:21Perry Wilson:Yeah. And this is a place where there is a real RCT. So probably the most famous, well-known RCT in the dietary world is the PREDIMED study, which is an RCT of Spanish people, which looked at the Mediterranean diet, and there is a substantial olive oil component of this. They had some people on a low-fat diet, some people on a Mediterranean diet olive oil, some people on a Mediterranean diet with nuts. And both of those two latter groups, the Mediterranean diet groups, including the olive oil group, had a much lower risk of major cardiac events. And so it's reasonable to say olive oil has been shown to be part of probably the most evidence-based diet we have for people at high risk of cardiovascular disease, that's about what we could say.
1:00:14Perry Wilson:Yeah, yeah. It's great.
1:00:15Emily Oster:You can use olive oil. Don't fry with it. It won't smoke too much.
1:00:19Perry Wilson:You can't fry in it. It doesn't get hot enough.
1:00:21Emily Oster:Yeah. Which brings us to avocado oil. That's a 70 % oleic acid oil with a pretty high smoke point and a neutral flavor. So certainly feels like one that would be better for frying with or for cooking at higher temperatures. Unfortunately, for those of us spending a lot of money on avocado oil, there is just a ton of adulteration of avocado oil on the store shelves. So there's a big study done by UC Davis that looked at products saying made with avocado oil or even just avocado oil itself. And 93 % of the avocado oil containing products contained other oils, sometimes unreported oils. Even the avocado oil in the jars, just like this is pure avocado oil, was widely adulterated with canola, sunflower, and safflower oil, which are seed oils.
1:01:18Emily Oster:So in a lot of cases, you're paying a premium and still just getting seed oils. Interestingly, the same study looked or the same group looked at the olive oils and found very little adulteration. And from what I understand, I guess there's more standardization in the industry about olive oil. Like there's a lot of groups kind of monitoring and making sure that extra virgin is extra virgin and avocado oil just isn't there yet.
1:01:41Perry Wilson:Also, avocados are expensive, like capitalism. Like it's, you know, avocados are a lot more expensive than olives. And so it's like if you like it's the incentive to cheat is so much greater.
1:01:52Emily Oster:The incentive to cheat is very high, which is why there needs to be some regulators. But buyer beware when it comes to avocado oil. It's good in theory, but in practice, you might just be getting seed oil secretly. All right.
1:02:06Perry Wilson:So last thing that we should talk about is actual substitution trials. So we sort of have like kind of talked around these, but there are a few trials where they tried replacing animal fat with some kind of typically seed oils. And, you know, I would say on the whole, these trial, like there are some very early trials of this. So there's like a 1969 trial of like 850 men where they replaced for some of them, some of their animal fat with seed oils. And this caused quite a large decline in their cholesterol that sustained. and ultimately they had lower rates of myocardial infraction, heart attacks, and so on.
1:02:54Perry Wilson:So that definitely is a positive in the direction of seed oils. Yep.
1:02:59Emily Oster:Yep. Very famous study.
1:03:00Perry Wilson:There are other studies which are sort of show the opposite.
1:03:05Emily Oster:There is. The one that you hear a lot about is the Sydney Diet Heart Study, which is, for this type of study, a little bit on the small side. This was published in the BMJ in 2013. 458 men only from Sydney who were randomized to a diet that was high in safflower oil and safflower oil margarine to replace animal fats. This study, the control group here was no specific dietary instruction and no study foods. So a little bit of an uncontrolled control group. And they actually found a higher overall mortality, although barely statistically significant, in the group that got randomized to the addition of safflower oil and safflower oil margarine.
1:03:54Emily Oster:Yeah, small study, not a great control group, just men in Sydney. The way that I parse a lot of this data when you kind of see things going in one direction, you see things going in the other direction, is to say probably it doesn't matter that much overall. So there's just noise in the system. And I don't think you're necessarily going to save your life by only adding margarine to your diet or only adding avocado oil to your diet. You probably have to do larger scale lifestyle shifts to really meaningfully impact outcomes. And the substitution of a single fat is not going to do too much.
1:04:31Perry Wilson:Yeah, I think another way to say that is, you know, if you look overall at people's diet, higher consumptions of some foods are associated with more fried food, more ultra processed food, more dietary patterns overall that we know to be associated with higher rates of different kinds of health events. but it's extremely difficult slash impossible to isolate some particular acid or some particular oil and say, you know, this is the thing. Like if only you pull this out of your diet, you would be cured. It's just not how it works.
1:05:08Emily Oster:It's never one thing, guys. It's never one thing, guys.
1:05:11Perry Wilson:Also, if you didn't have any of this, as we noted before, you'd be dead. So note. Right. Note. All right, Perry, are you a smash or pass on seed oils?
1:05:25Emily Oster:I'm a smash. I think broadly speaking, plant-based fats are probably better for you than animal-based fats, and seed oils are a member of that panoply. So I'm okay with it. Emily, smash pass. Yes.
1:05:39Perry Wilson:Likewise, I am a smash. I like a good seed oil. And also I like balance. So I'm happy to have seed oils and animal oils and all kinds of different fats. And you should choose. I will say I've written about this before. And a friend of mine, Craig, wrote to me to explain that the most important thing is to match your oil to the cooking thing you're doing. He said, I have beef tallow. I have duck fat. Then he listed a few other more obscure fats. And some of them were good for some things and some of them were good for others. And I thought that was exactly the way to look at it. Sometimes you need a seed oil.
1:06:20Perry Wilson:Sometimes you need butter. Sometimes apparently you need duck fat if you're my friend, Craig.
1:06:25Emily Oster:Thanks, Craig. That's it for seed oils, your mailbag question of the week after the break. We all miss the 90s, the music, the shows, the outfits, and without a doubt, the snacks.
1:06:39Perry Wilson:Simple Mills is bringing back the golden age of snacking. They taste delicious like the snacks you grew up with, only they're made with real ingredients like watermelon seed flour, almonds, cashews, flaxseed, and organic coconut sugar. Fancy.
1:06:53Emily Oster:You'll love the throwback taste of cheddar pop-ums, the nostalgic flavor of mini crunchy chocolate chip cookies and the familiar crunch of honey cinnamon sweet thins.
1:07:03Perry Wilson:Available in snack packs that are easy to toss into lunch boxes, backpacks, or your own bag. Simple Mills snack packs are simply the coolest.
1:07:11Emily Oster:Simple Mills. Throwback taste. Grown-up ingredients.
1:07:15Perry Wilson:I had a huge body flare-up again. Was itchy from head to toe. And I applied to topical steroids like I normally do when I'm in moments of crises like this. You know, I normally wait about 30 minutes and I'm like, okay, so this is not working. And so I applied again and waited another 30 minutes and I'm like, this is not going down. What is going on here? And that's when the anxiety kind of kicked in because I was like, what is happening? My entire world and idea of what it was to manage my eczema at that time completely crashed. That's when I started doing research for the first time. And then I realized, wow, I think the medicine stopped working for me and my body was just going through maybe a withdrawal process.
1:08:06Emily Oster:This is Skin Queries. Listen on the iHeartRadio app, Apple Podcasts, or wherever you get the stories that make you feel understood. I'm Martha Stewart from the Martha Stewart Podcast. In this special episode brought to you by McCormick Signature Seasonings, I got to chat with Reddit founder Alexis Ohanian about his new venture, Retrieve Air. We also get to talk about his family life and playing the weekend chef. I'm a simple man. I use honey from the farm and I got my crepe. That's it. The girls like their Nutella. That's my breakfast ritual. I'm usually phoning in lunch a little bit because I'm really planning on a delightful dinner.
1:08:46Emily Oster:The girls really like steak. I spoil them. So even if I'm doing kebabs, I'm using ribeye, I'm doing it right. Okay, well, please. Listen to the full episode of the Martha Stewart Podcast wherever you get your podcasts.
1:09:04Emily Oster:And we are back with our question of the week. If you have a question for Emily or I, leave it for us at wellnessactually.fm. We'd love to hear from you and answer your question on the air. Let's play it. Hey, Emily and Perry. My kids are back in school. It's too late for me, but for everyone else, how do you not get sick? Thanks. All right. So Emily, what are your wellness hacks to prevent getting sick once all the kids are back in school?
1:09:34Perry Wilson:So my best wellness hack is that my kids are old. So that's been just totally crucial for me because older kids get sick less than younger kids because I think there's less licking of faces. I mean, maybe that's not true. I don't know what it is. Anyway, it's been good. But I don't think it's really a great answer to this, except for wash your hands. You should wash your hands because you touch your face far more than you think. But a lot of what people tell you, like take this immunity booster, that stuff's just a bunch of crap. I don't know. Do you take a bunch of crap immunity boosters, Harry, like an idiot?
1:10:07Emily Oster:Nope. Nope. I don't. Nope. There's no preventative value for like mega dosing vitamin and see or anything like that. And yeah, wash your hands. That is the number one, two, and three thing to do. And my kids know as soon as they walk in the door, they're going to put their bag down and wash your hands. I'm hopeful that they do it at school from time to time too, but hope springs
1:10:26Perry Wilson:The other thing is sleep. So sleep is actually quite good for your immunity. I think the sort of terrible combination for parents of toddlers is that your children are going to a place designed to make them sick. Like that's on purpose they're supposed to get sick. So they develop immunity for later and so on. And also you're not sleeping enough often. And so the combination of sleep deprivation and constant exposure to pathogens is really problematic.
1:10:57Emily Oster:Sounds good. Get your sleep, wash your hands.
1:11:02Perry Wilson:All right, that's it for us today. Stick with us next week when we'll ask, what's the deal with artificial sweeteners?
1:11:14Perry Wilson:Wellness Actually is produced in association with iHeart Media. Our senior producer is Tamar Avishai. Our executive producer at iHeart is Jennifer Bassett. Our theme music is by Eric Deutsch. And our content is for educational purposes only.
1:11:29Emily Oster:If you like the show, help other people find us. Leave a rating and review on Apple Podcasts or your podcatcher of choice. And help us spread the word about the show. You can follow us on Instagram at wellnessactuallypod. And don't forget, we want to hear from you. Head over to wellnessactually.fm and leave us a question for our mailbag or suggest a topic for a future show. We'll let the influencers have the last word. I like olive oil and butter, coconut oil, and things like avocados and some Brazil nuts and walnuts and stuff. So for me, I don't think seed oils necessarily will kill me, but guess why I know they won't kill me?
1:12:05Emily Oster:Because I don't eat them.
1:12:17Emily Oster:We all miss the 90s, the music, the shows, the outfits, and without a doubt, the snacks.
1:12:24Perry Wilson:Simple Mills is bringing back the golden age of snacking. They taste delicious, like the snacks you grew up with, only they're made with real ingredients, like watermelon seed flour, almonds, cashews, flaxseed, and organic coconut sugar. Fancy.
1:12:38Emily Oster:You'll love the throwback taste of Cheddar Pop-Ums, the nostalgic flavor of mini crunchy chocolate chip cookies, and the familiar crunch of honey cinnamon sweet thins.
1:12:47Perry Wilson:Available in snack packs that are easy to toss into lunchboxes, backpacks, or your own bag. Simple Mills snack packs are simply the coolest.
1:12:56Emily Oster:Simple Mills. Throwback taste.
1:12:58Perry Wilson:Grown-up ingredients.
1:13:00Emily Oster:Honey, Felipe sent another photo. From Argentina? How? With T-Mobile, of course. Mira, he's video calling us. Hola, familia. Did you get my photos? We did.
1:13:11Perry Wilson:They're so pretty.
1:13:12Emily Oster:Here to share every moment with T-Mobile. Enjoy data roaming at no extra charge in 21 Latin American countries. Switch now on the T-Life app or T-Mobile.com slash connectate. Qualifying plan required not for extended international use. You must reach out in the U.S. and primary usage must occur in our network. Visit T-Mobile.com.
1:13:29Perry Wilson:Hey, y 'all. What's up? This is Lauren LaRosa from the latest with Lauren LaRosa, the podcast. Remember Varnell Hill from the 90s sitcom Martin? He's back. And now on Paramount Plus, more than 30 years later, Tommy Davidson is stepping back into the spotlight in an all-new Martin spinoff, The Varnell Hill Show. And Varnell has just one question. Did you miss me? Now he's got network execs, a wild writer's room, family drama, and everyone telling him he's passed his prime. Varnell isn't slowing down, bringing raw, unfiltered jokes every step of the way. From executive producer Martin Lawrence, The Varnell Hill Show is now streaming exclusively on Paramount+.
1:14:06Perry Wilson:This is an iHeart Podcast. Guaranteed human.
From the publisher
This week, Emily and Perry dive into the slippery world of seed oils. Canola, vegetable, safflower, yes, even avocado: why have these plant-based oils gotten such a bad rep compared to their animal-based counterparts? How does processing and frying play in? Is it beef tallow's world and we're just living in it? Note: this episode is best enjoyed with a big plate of fries.
Plus: a disappointing heart drug, the military is no longer testing testosterone (thanks to us??), and exciting news in the pig kidney community.
Submit a question for our weekly mailbag at wellnessactually.fm.
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