Science Vs - Intermittent Fasting: Hungry for Facts?

Episode Date: March 28, 2024

Fasting diets are going bonkers right now — some tech bros are down to one meal a day! And health-fluencers claim that intermittent fasting can help you lose weight, live longer and even fight cancer. But meanwhile, recent headlines are screaming that these diets might actually be dangerous — and linked to death from heart disease. Can science sort this all out?? We speak to nutrition researchers Dr. Krista Varady and Dr. Courtney Peterson, as well as cancer researcher Professor Valter Longo.  Mental health and disordered eating resources are here: spotify.com/resources  Find our transcript here: https://bit.ly/ScienceVsFasting In this episode, we cover: (00:00) Fasting: the fad and the fears (03:07) Does fasting help you burn fat? (07:40) How much weight do people lose with intermittent fasting? (08:47) Is this just calorie restriction? (13:17) Can fasting help you live longer? (19:50) Can fasting fight cancer? This episode was produced by Kaitlyn Sawrey, Nick DelRose and Wendy Zukerman with help from Michelle Dang, Rose  Rimler, Joel Werner and Meryl Horn. We’re edited by Blythe Terrell, with extra editing help from Caitlin Kenney and Annie-Rose Strasser. Fact checking by Eva Dasher and Michelle Dang. Mix and sound design by Peter Leonard and Bobby Lord. Music by Peter Leonard, Emma Munger, Bumi Hidaka and Bobby Lord. A huge thanks to all the researchers we got in touch with for this episode, including Dr Peter Chisnell, Dr Mikkel Holm Vendelbo, Dr Jiahong Lu, Dr Dorothy Sears, Prof. Mark Mattson, Dr James D Dvorak, Dr Calloway Scott, Professor Richard Billows, Professor Nancy Worman, Dr  Barbara Kowalzig  and the University of Alabama, Birmingham. Also thanks to Kimmie Regler, Helen Zaltman, Frank Lopez, 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

Hi, I'm Wendy Zuckerman and you're listening to Science Versus. This is the show that pits facts against foregoing food. Today we're tackling intermittent fasting. Can it make you shed pounds and live a healthier, longer life? Intermittent fasting diets are basically where you don't eat for a certain period of time whether you have this really long gap between dinner and breakfast or perhaps you're just eating one meal a day this is also called omad get it one meal a day and these fasting diets are going bonkers right now follow the gossip mags and you'll see that celebs are all over this, from Chris Pratt.

I did something called intermittent fasting. To Vanessa Hudgens, Kourtney Kardashian and even Hugh Jackman. Every day what I do is I eat for eight hours and I fast for 16. I actually got the diet from Dwayne, The Rock Johnson, his mate of mine. We first ate up the science on fasting a few years ago. But since then, the hype around fasting hasn't been slowing down. In fact, it feels like these diets have kind of taken on a life of their own. Headlines are screaming, quote,

I did intermittent fasting and it changed my life. It's all over TikTok and Instagram and podcasts. Tech bros and health fluences can't get enough. The data behind fasting is so strong. Like whose idea was it three meals a day anyway? It's absolutely one meal a day, no ifs, ands, or buts. We've been hearing that not only does fasting rev up your metabolism, making you shed pounds, but that the benefits of fasting go way beyond weight loss. Going hungry could be the key to a healthier and even longer life.

Fasting reduces the risk of cancer, Alzheimer's. So, there's all these claims about how amazing fasting is for you. But then, some research came out last week that spoiled the fun, just like someone cooking fish in the office microwave. Because it suggested that intermittent fasting might actually be dangerous. An alarming new study on intermittent fasting suggests that intermittent fasting could lead to a 91% higher risk of cardiovascular death. 91%. So what's going on here? Today on the show, we are dropping our spoon back into the science soup to find out, one, if you want to lose weight, how helpful are these diets? And two, can fasting diets make you live longer or not?

When it comes to fasting, there's a lot of... The data behind fasting is so strong. But then there's science. Science vs. Fasting is coming up after the break. It's really not important to me to have a lot of things to show off, fancy cars, you know, a giant home. Those things are just not part of who I am. But I've been coached and I've learned through my advisor

that it's not one size fits all. Everyone has their own preferences. Everything that I do with Edward Jones is tailored to who I am. Edward Jones. We do money differently. Visit edwardjones.ca slash different. It's season three of The Joy of Why, and I still have a lot of questions. Like, what is this thing we call time?

Why does altruism exist? And where is Jan 11? I'm here, astrophysicist and co-host, ready for anything. today's show. every other Thursday, starting February 1st. Welcome back. On today's show, we're tackling fasting. And we'll start by looking into weight loss. So online, people say that fasting puts your body into this special state that ramps up your metabolism and helps you lose a ton of weight.

So to find out what's going on here, we sent Caitlin Sorey to the University of Alabama in Birmingham. It's our pleasure to welcome you to Birmingham. Caitlin used to be our senior producer, and she's in Alabama to meet researcher Courtney Peterson. Hey! Hi! Who's going to hook Katie up to a state-of-the-art machine to measure how her body responds to fasting.

And because people argue that fasting ramps up your fat burning. So this machine is going to measure how much fat you're burning. Courtney is going to find out if that's true. If fasting really does change how Katie or anyone else burns fat. So we'll have you try 18 hours of fasting. So first up, she took some baseline measurements. Katie left the lab, had her final meal. Rammed a sandwich in my face. And stopped eating at 5pm that day. The next morning, she headed back to Courtney's lab at about 11am. And heads up, Katie does not sound as chill as Hugh Jackman after she's been fasting. I'm running late for this test because the bloody printer wouldn't work. Then I couldn't get a sandwich to have after the test. So now I'm

frustrated and just like moody and emotional. And I just need some sugar in my face, honestly. Now that Katie is good and hangry, Courtney will measure how much fat her body is burning. And to do that, Courtney puts a weird-looking hood contraption over Katie's head. Just picture this giant plastic device that kind of looks like a space helmet. And it's connected to this plastic covering,

which, as you'll see, we'll put the hood over you and then we'll tuck the plastic covering around your body. It's that way we create an airtight seal so all the air that you breathe in only comes from our tube and all the air that you breathe out we can measure it. Nothing getting in or out without you guys measuring it. That's the game. That's correct. Alright so we're inside the hood. And just stay very calm. Breathe normally. Now, to understand why Katie's breathing is important here,

you need to know that mainly your body burns sugars and fats for energy. And when it does that, some of that fuel gets converted into carbon dioxide, which you breathe out. And that is actually what Courtney is measuring in that snazzy helmet. She's looking for changes in the amount of carbon dioxide that Katie is exhaling. The less carbon dioxide you breathe out relative to oxygen, the more fat you're burning. Weird. Okay. So before Katie was fasting, Courtney could see that about half of her energy was coming from burning fat. How did fasting change that? So on day two, after you

were fasting for nearly, I think it was 18 hours. Yeah, it was 18. It was hard. We found about 70% of what you're burning now is fat. Wow. So you had a big increase in your fat burning. So you can see these are... Yeah. So at the start of the experiment, when Katie wasn't fasting, about 50% of the energy that she was burning was coming from fat.

And that went up to around 70%. Katie has ramped up the amount of fat that she's burning because her body started looking for more sugar to burn. But because she wasn't eating more sugar, her body had to look elsewhere for energy. And so it turned to fat and started burning more of it. Other studies have found this kind of thing too. If you've been fasting, you really are in this fat-burning mode

and your body kind of revs up its ability to burn fat. Now, that fat-burning mode doesn't last forever. As soon as Katie rips off the hood... It's time to eat! ..and stuffs her face with a pumpkin muffin... OK, so I'm so starving. Oh, my God. ..her body gets back its sugar fix and all returns to normal. She starts using sugar for energy.

But the fact that we burn more fats, at least while we're fasting, is giving the internet some food for thought. Because it sounds like this is going to mean that you lose a ton of weight. Is that true? We talked to Krista Varity from the University of Illinois, Chicago about this. She's run trials on weight loss and fasting in hundreds of people, probably more than any other researcher out there. And Krista told us that, yeah, people do lose weight on these fasting diets. And that's definitely the main thing that we see. So there's always like a range,

like some people don't lose any weight, but the majority of people tend to lose on average like 10, 15 pounds. So for your standard intermittent fasting diet, where you say skip your breakfast and have your first meal at lunchtime, a few trials have found that after several months, on average, people tend to lose between 5 to 15 pounds. So that's around 2 to 7 kilos. But every now and then, she'll see these dramatic results. So for example, she told us about this one person who was on this diet for several months, really wanted to lose a bunch of weight and lost about 60 pounds. They were extremely happy. They look like an entirely different person. It's really interesting to see somebody be like transformed. How much weight you lose can depend on a bunch

of things, like how heavy you are to start with, what you're eating when you're not fasting, and what your eating window is. So Courtney told us that there's a growing body of good evidence that if you squish all of your food into an eight-hour period, like you're eating from 11am to 7pm, there's a good chance you'll lose weight. But this all did make us think, wait a sec, are you really losing weight because fasting is putting you into this special fat-burning mode? Or could it be that something much simpler is going on? You're just not eating as much. Because if you're not eating for a big chunk of the day, then over the course of a week,

you're probably putting less pies down your pie hole than you used to. So you're just losing the weight because you're eating less. And to find out which idea was right, special metabolism theory or you're just eating less, Courtney from the lab in Alabama did this one small study to see what would happen if you got people to fast but didn't change how many calories they were eating. So these people ate the normal amount of calories for five weeks, but they just had to down it in a smaller window of time, like you do with some of the fasting diets.

And Courtney made sure that she knew what they were eating. We had all our participants either eat the meals in our kitchen or they had to eat their meals on Skype so that we could make sure they were actually eating all the food that we provided them. Oh my God. Now, you would think that if there was something special about fasting that people would lose weight even if they were eating the same number of calories right? But they did not lose weight. So we now think that this intermittent fasting does not help you burn more calories. So bottom line, why does Courtney think that people drop

pounds when it comes to fasting? Because they're eating less. That's what our data suggests. It's simply because they're eating less. Several studies have now backed up this idea. Okay, so what all this means is that when you're on a fasting diet, you'll probably find yourself eating less. That is, unless you have scientists force-feeding you via Skype. And if we're not putting so much crap down our trap, less mullet down our gullet, not so much jelly in our belly, well, that's probably the main reason we're losing weight. But still, if you are interested in losing weight, this all sounds pretty promising.

Except for this one little thing. Jelly is great. And not eating sucks. Remember how hard it was for Katie? I just need some goddamn sugar in my face, honestly. Why do people want to do this to themselves? So, does it get any better? Or if you go on one of these diets, will you just be miserable and hungry?

Well, the few studies that have tracked people's hunger levels during these fasting diets actually shows a really mixed picture. So sometimes people feel fuller as the diet goes on and they get used to it, but sometimes they just stay hungry. Katie kept fasting for about 16 hours each day and she did it for three weeks. Three weeks. Three weeks. Brought her into the studio. How are you finding it? Less hangry.

Really? Yeah. In the beginning, I reckon I was going to bed pretty hungry. I was like, I'm going to chew the side of the bed. I'm going to chew on this pillow. So now I'm just not as hungry. So that's weight loss. But while you're digesting that, wellness bros and health fluences

say that fasting can do so much more than help you slim down. Some people say that with the power of fasting, it can help you live longer and even fight cancer. Could fasting really do that? Or is this diet actually more dangerous than we thought? It's all coming up after the break. First, breakfast.

Welcome back. Today, we're chewing up the research on fasting diets. We just found out that fasting can help you lose weight. And now we're going to tackle some of the bigger claims about this diet. Starting with whether fasting can make us live a longer and healthier life. Because the internet bros and goop fluences out there say that one of the benefits of fasting is that it can slow down the aging process. People that fast a lot end up looking a lot younger than they actually are. To enhance regeneration, decrease inflammation.

This is great for dementia, improving your memory, focus, concentration. And they say that this is possible thanks to this very science-y sounding word. Something known as autophagy. Autophagy, autophagy, autophagy. We're going to talk about autophagy. What is autophagy? Okay, so not to be that guy at the party, but it's actually pronounced autophagy. That's according to the five ancient Greek speakers that we asked.

But of course, the big question isn't how do you pronounce it? It's what is it? Well, autophagy is a process that works inside your cells, and it helps your cells to replace damaged parts. And it does it in this really cool way. The cell literally eats chunks of itself. In fact, that's what the word autophagy means in ancient Greek, self-eating. It's the little cannibal inside us all. And the key is that the cells can recycle those old dud pieces to make new shiny parts. Here's researcher Krista Varity again. It's kind of a weird term. The body starts

cleaning itself up, kind of like gobbles, gobbles itself up. The story you'll hear online is that fasting ramps up autophagy, which means you'll be getting rid of more bung cell parts and creating new shinier parts and keeping us all healthy, whether that means fighting off Alzheimer's or making us live longer. And a lot of the claims that you'll hear come from studies in animals. So like when fruit flies, mice or rats are put on fasting diets, they tend to live longer. And a recent study in fruit flies found that fasting ramps up their autophagy.

And this was actually a really important reason as to why they lived longer. So now there's this big question about whether fasting makes you and me, you know, humans live longer or even boosts autophagy in us. Which takes us back to Courtney, our researcher from Alabama. Wendy.

Who also studies autophagy. Yeah, absolutely. And she told me that knowing if intermittent fasting is ramping up autophagy in you and me, in humans, it's tricky. So it's actually really, really hard to measure in people. When scientists do these autophagy studies in flies or rats, sometimes they'll mess with their DNA, remove bits of tissue, kill them, which can be a tough sell for a volunteer in a scientific study.

So when researchers like Courtney are trying to sort out this autophagy question, they have to get creative. Several years ago, Courtney got almost a dozen people to fast for 18 hours. That meant they could only eat between 8 a.m. and 2 p.m. Harsh, right? Right, because then if there's a benefit, we'll see it.

They did this for four days, and then as a control, she got the same people to do a much nicer fast, where they would eat from 8 a.m. to 8 p.m. And what we did is we collected blood cells, and then we isolated their DNA. And what Courtney wanted to know was whether the activity of these genes that have been linked to autophagy ramped up after people were on this hectic fast.

And so if you picture how autophagy works, you've got some proteins toddling about, picking up all that trash, the damaged bung cell parts in your body. And then you've got the incinerator where we're like, okay, bring in the trash. We're going to incinerate this and then make new things, new proteins out of it. Well, Courtney zoomed in on one gene that creates the outside casing of that incinerator. And what she found is that after people did their 18-hour fast, that gene did get more active. Amazing. And so you found that after fasting,

we have more incinerator casing. Exactly. Exactly. It's just super cool. I wasn't expecting to see such striking results. Courtney's research is exciting, but it's not all cupcakes and cookies. We actually have a handful of other studies that have looked at this autophagy question in people, and they're actually a bit conflicting. So some, like Courtney, suggest that intermittent fasting does boost autophagy in us, but others don't. And then we have some research that has tried to tackle this question of does fasting boost longevity in a completely different way? Scientists will follow people for years to see if those who fast

live longer than those who don't. Some of these studies are done in people with heart failure or diabetes. And it's just important to know that the research that we have at the moment that does this, it's far from perfect. So a lot of this research will survey people for just a couple of days about their eating habits. And then years later, see, are you dead yet? So we don't actually know if they were practicing fasting for that whole time. But still, what these studies tend to find is that people who said that they were fasting for around 16 hours, they don't live longer. And just generally, like even away from those studies,

Krista reckons that the hype around fasting as a longevity booster is a bit overblown. First and foremost, there's never been anything showing in humans that either calorie restriction or fasting helps people live longer. Those are all studies done in worms and yeast and mice that we're just kind of extrapolating from. So, as for the evidence that fasting will make you live longer, the proof is in the pudding. Which for now, I'm eating. But there is an area of fasting research that is racing ahead. And it's in cancer. Fasting may actually weaken tumors.

Researchers are looking into the benefits of starving cancer. Now when we first heard about this, we were like, wait, what? But there is actually some good science as to how this might work. You see, many types of cancers love sugar. They just, like, eat it up. And this has been known for ages. But more recently, scientists wondered, well, if cancer loves sugar so much,

and when you fast, your body kind of runs out of sugar, would this cut off the cancer's food supply? Walter Longo, a professor in aging at the University of Southern California, told us what it might be like for a cancer cell when someone is fasting. The cancer cell, for the first time, it finds itself in a very strange environment that has never seen before. The idea is that once the cancer is confused and weakened by fasting, if you then add conventional medicine like chemotherapy,

it's like a one-two punch. So combined with fasting, they're hoping that the chemo is able to search and destroy every cancer cell. Call it that by confusion. And the reason that I call it that is because it's really about the cancer cells being able to adapt to this very confusing environment where everything is changed. To test this, Walter gave a bunch of mice cancer. And he did it in this kind of creepy way. The cancer cells are injected into the mouse.

The mass starts growing. And eventually, if you don't do anything, that will kill the mouse. Wow. To save the little mousies, Walter then put them on a fast, as well as giving them chemo. And it worked. Way more of the mice survived, compared with mice that just got chemo but didn't do the fasting. Other scientists doing similar work have found this too. That using that one-two punch, chemo and fasting, some mice were living cancer-free.

We cured lots of mice when we combined the two. So it's really interesting how the combination can be so much more powerful than each intervention alone. Volta and other scientists are now researching whether fasting can help to fight cancer in people, which can be a little more complicated than working with mice. In fact, Volta told us that just convincing some experts to get patients to try this can be tough because many doctors and

dieticians have been taught that if you have a patient going through chemo, you need to get them to eat, not fast. Years ago, he'd go to conferences and doctors would say, you know, this is ridiculous. And it's like, oh, you know, will I tell my patients to fast during chemotherapy? Absolutely not. But little by little, things have been changing, thanks to some exciting crumbs of research. Like, just recently, this one trial came out which had more than 100 people with breast cancer.

Some went on a fasting diet three days before chemo as well as on chemo day, while the others just stuck to their regular diet. The research team, which included Volta, took images of the patients' tumors and found that for those who were on the fasting diet, it was more likely that their tumors had shrunk. The more the cycles of the fasting diet, the more shrinking of the tumor and the more killing of the cancer cells within the tumor. Another study from a few years back of over 2,000 women who had breast cancer

found that for those who fasted more than 13 hours each day, they were less likely to get breast cancer a second time. And then, just quickly, recently in Italy, researchers did this study where they just wanted to see if fasting diets were safe for people with advanced cancer, and they found that it was. But then they followed around 75 people in that trial for years to see if it actually helped with their survival. And it looked like it did.

It definitely wasn't a cure for everyone, and in fact around half the people in the trial died from cancer within a few years. But the authors said that this was still better than expected for these patients who, remember, had advanced cancer. And in that trial, there was something that got Volta really excited. There was this handful of patients who were what the researchers called extraordinary responders. They were all stage four colorectal, breast, lung, and pancreatic cancer.

I mean, the type of patient that all oncologists would say, this patient is going to die very soon. And all of them went into remission, right? So, yeah, so I think that certainly brings everything to a different level. So clearly fasting isn't a silver bullet for cancer. But this research suggests that for some people with some cancers, when combined with chemo, fasting could be a game changer. I hope it gives a lot of hope.

I hope it gives hope. Obviously, you still have some doubts because you never know. But I mean, I say overall that the results have been very positive. Do you think that all patients right now who have cancer and are going through chemo should start a fasting diet? No, I don't. So it looks very, very promising, right? We'll all be very surprised if it didn't work, but what if, right? What if it makes it worse for some patients and, or, you know, it doesn't work. So, yeah, I would say that all patients with advanced stage cancer or cancer for which there is nothing working

should talk to their oncologist. One of the uncertainties with cancer patients is that some fasting diets could cause other problems, like people might lose too much weight and then become malnourished. And away from cancer, this got us wondering, are there any other downsides to fasting? You know, other than losing the joy of eating.

Which takes us to the new research that came out last week, which seemed to suggest that fasting diets could actually be dangerous. This made big news all around the world. Well, now to a recent health alert that's causing quite a stir. We're talking about intermittent fasting. This was really shocking. Intermittent fasting, is it dangerous? So this study, which, by the way, hasn't been peer reviewed yet. I know, I know. But it found

that people who said that they were eating within an eight-hour window, so let's say fasting for 16 hours, had a higher risk of dying from heart disease years later. And this actually isn't the first study to find this kind of thing, which might sound a little scary, but some scientists have been quite critical of these kinds of studies because they're not randomised control trials. So we really have no idea of knowing whether these deaths had anything to do with fasting diets or perhaps this is just kind of a coincidence. And I know this is frustrating. It's like, are these diets dangerous or not?

But the truth is, we just don't have a lot of long-term data on people going on these diets. And then there are some other things to think about. Like sometimes fasting diets can mask other things going on, like eating disorders. Some people do report feeling constipated, dizzy or weak. And then there is this thing that you might not expect. Gallstone formation and the need for a gallbladder removal goes up. Oh, wow. Gallstones are lumps in the gallbladder, which can be really painful. So that's just an example of how you cannot think that everything is always going to go the way you want it to go.

And it's these kinds of surprising side effects that are why people should be a bit cautious before diving into fasting diets, particularly the more extreme versions. So when it comes to intermittent fasting, does it stack up like pancakes with maple syrup? Here's our conclusion. One, will you lose weight? Probably.

People on fasting diets tend to lose weight, and that's probably because they're eating less. It's not magic. Two, will fasting make you live longer? There's some exciting stuff happening in mice and rats and even fruit flies. But in people, the studies are like a mixed bag of lollies. And three, can fasting fight cancer?

Well, the most promising research is when fasting is combined with chemotherapy. And while we already know from the data that this isn't a miracle cure and it's not going to cure everyone's cancer, it still could help a lot of people. Let's wait and see. So to cap us off,

is this a wonder diet or a wonder why your friends are on a diet? And I think we've got to say it's a bit of both. There's some interesting work happening here, but the bro-hards and the healthfluencers are getting a bit carried away. What a surprise. That's science versus intermittent fasting. There are 147 citations in this episode, yes, and the last one is about gallstones. If you want to read about gallstones, fasting, anything we talked about in this episode, then just go to our show notes and click on the link to the transcript.

And to see a photo of what Katie looked like when she was wearing that helmet to measure how much fat she was burning, come to our Instagram account. We're at science underscore VS. And if you're on TikTok, then come say hello because I'm there too. I'm at Wendy Zuckerman. Thanks for listening. This episode was produced by Caitlin Sorey, Nick Delrose and me, Wendy Zuckerman,

with help from Michelle Dang, Rose Rimler, Joel Werner and Meryl Horne. We're edited by Blythe Terrell with extra editing help from Caitlin Kenney and Annie Rose Strasser. Thanks to all of the researchers that we got in touch with for this episode, including Dr Peter Chisnell, Dr Mikkel Holm-Vendelboe, Dr Jianghong Lu, Dr Dorothy Sears, Professor MarkVendelboe, Dr. Jianghong Liu, Dr. Dorothy Sears, Professor Mark Mattson, Dr. James D. Dvorak, Dr. Calloway Scott, Professor Richard Billows, Professor Nancy Warman, Dr. Barbara Kowalczyk, and the University of Alabama, Birmingham.

Also, thanks to Kimmy Regla, Helen Zaltzman, Frank Lopez, the Zuckerman family, and Joseph Lavelle Wilson. I'm Wendy Zuckerman, back to next time.