Science Vs - Fasting Diets: What's the Skinny?

Episode Date: March 29, 2019

Fasting diets are all the rage right now and health-fluencers claim it can help you lose weight, live longer and even fight cancer. So what does the science say? We speak to nutrition researchers Dr Krista Varady and Dr Courtney Peterson, as well as cancer researcher Professor Valter Longo. Check out the full transcript here: http://bit.ly/35FYJoP Selected references: Krista’s study comparing alternate day fasting with regular dieting, which found they had similar weight loss after one year.Courtney’s study which measured metabolic changes after time-restricted feeding without weight loss.Valter’s paper summarizing the studies in fasting and cancer.  Credits:This episode was produced by our senior producer Kaitlyn Sawrey and Wendy Zukerman with help from Michelle Dang, Rose Rimler, 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. Music by Peter Leonard, Emma Munger 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 the Kimmie Regler, Helen Zaltman Zukerman Family, Frank Lopez and Joseph Lavelle Wilson.  Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hi, I'm Wendy Zuckerman and you're listening to Science Versus from Gimlet. This is the show that pits facts against feeling famished. On today's show, fasting. Can it make you slimmer and healthier? Fasting diets are basically where you don't eat for a period of time, whether it's going without food for a day or two, or just leaving this really long gap between dinner and breakfast. And this way of eating, called intermittent fasting, it's all the rage right now. Seems like everyone's getting into it. According to the gossip mags,

Chris Pratt, Kourtney Kardashian and even Hugh Jackman are doing it. 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, who's a mate of mine. Internet bros and health fluences are getting into this foodless frenzy too. Let's talk about how to get lean and ripped with intermittent fasting.

But beyond getting ripped, there's a lot of buzz that fasting can make us healthier and do all sorts of impressive things. The medical community is saying it can work. There could be benefits beyond losing weight. Fasting reduces the risk of cancer, Alzheimer's, and can help us live longer. And if a diet could do all this, that would be amazing.

Which is probably why a lot of us have questions about it. In fact, Google says that fasting was one of the top trending diets in the US last year. So obviously, we are hungry for knowledge, starved of information we can trust and fed up with internet celebs. That's why today we are finding out, is any of the hype real?

Like, what can science actually tell us about fasting? When it comes to fasting, there are lots of opinions. But then, there's science. Science vs Fasting is coming up just after the break. Welcome back. On today's show, we're tackling fasting. And we wanted to start by finding out what happens to your body when you fast. So for that, we sent our senior producer, Caitlin Sori, to the University of Alabama in Birmingham. It's our pleasure to welcome you to Birmingham. Caitlin is here 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. That is, will fasting really change how Katie burns fat? So we'll have you try 18 hours of fasting. So Katie left the lab,

crammed a sandwich in my face, and stopped eating at 5pm that day. The next morning, she headed back to the lab at about 11am. And heads up, Katie does not sound like Hugh Jackman after she's been fasting. She's more of the hangry type. 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. bloody printer wouldn't work. Then I couldn't get a sandwich to have after the test. So now, like, 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 this crazy-looking hood contraption over Katie's head. It's like a 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.

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. Right, so we're inside the hood. And just stay very calm.

Breathe normally. To understand why Katie breathing is important, you need to know that your body mainly burns fats and sugars for energy, and when it does that, some of the fuel gets converted into carbon dioxide, which you breathe out. And that's 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. OK. 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... Katie has ramped up the amount of fat she's burning because during the fast, she used up a tonne of sugar and she wasn't eating any more of it, so her body had to look elsewhere for energy

and it turned to fat and started burning more of it. Other studies into fasting 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, it 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. Okay, so I'm so starving.

Oh my God. Her body gets back its sugar fix and all returns to normal. But the fact that we burn more fat, at least when we're fasting, is giving the internet some food for thought. Because it sounds like this means you're going to be losing a ton of weight. Is that true? We asked Krista Varity from the University of Illinois, Chicago about this, and 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 really fast that, yes, people do lose weight on these fasting diets. So we always see weight loss and people tend to lose about anywhere from like 10 to 30 pounds or so. Yeah, yeah, 10 to 30 pounds.

Krista says that how much weight you lose can depend on a bunch of things, like how heavy you are to start with and how long you stick with it for. But Krista has seen some dramatic results in people who are overweight. Like after several months of this diet, someone lost 60 pounds. They were extremely happy. They look like an entirely different person. It's really interesting to see somebody be like transformed over the years. That is super impressive. But we wanted to know why are you losing weight with these diets? Is it because fasting puts you in a special fat-burning mode, like what happened to Katie? Well, Krista says that although you can see changes to your metabolism when you're fasting, like switching from burning sugar to burning fat,

that's probably not the main reason why you're losing weight on these diets. There's something much simpler going on. I don't think there is anything magical to it. I think it's just kind of fooling the body into eating less. Yeah, if you're not eating for a big chunk of the day, then over the course of a week, you're probably going to be putting less pies down your pie hole than you used to. Courtney from the lab in Alabama agreed with this when we asked her, why do people lose weight? Because they're eating less.

That's what our data suggests. It's simply because they're eating less. Several studies have backed this idea up. So, for example, Courtney did this one small study to see what happened if you have people fast but you don't change how many calories they're eating. So she got people to eat their normal amount of calories for five weeks, but they were only allowed to eat during a small

window of time, like you do with some fasting diets. And Courtney made sure 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'd think that if there was something special about fasting people would lose weight even though they were eating the same number of calories. But they did not lose weight. So we now think that this intermittent fasting does not help you burn more calories. Conclusion. 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 not putting so much crap down your trap, less mullet down your gullet, not so much jelly down your trap, less mullet down your gullet, not so much jelly in your belly. Well, that's probably the main reason you're losing weight. So, this all sounds pretty promising. Except for one little thing. Jelly is great and not eating sucks.

Remember how hard it was for Katie, our senior producer? I just need some 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 we have tracking people's hunger levels during fasting diets actually show a really mixed picture. So sometimes people do feel fuller as the fasting diet goes on and they get used to it.

But others just stay hungry. Katie has actually stuck to the fasting diet. Well, she's been fasting for about 16 hours each day 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. And Katie reckons she's lost a bit of pudge too. So that's weight loss.

But while you're digesting that, Silicon Valley bros and body hackers say that fasting can do much more than help you slim down. Some people say that the power of fasting can help you live longer and even fight cancer. Could fasting really do all that? It's not as wild as it seems. And it's coming up after the break. Welcome back.

Today we are chewing up the research into fasting diets. We've 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 actually make us live a longer, healthier life. Because the internet bros and goop fluences say that one of the benefits of fasting is that it can slow down the ageing 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 idea. Something known as autophagy. Autophagy, autophagy, autophagy. We're going to talk about autophagy. What is autophagy?

So this science-y sounding word, it's derived from ancient Greek. And to find out how to properly pronounce it, we tracked down five people who speak ancient Greek. That's right, there are bigger nerds than us out there. Now, they all told us slightly different things, but it tended to be something like autophagy. So that's what we'll go with. Okay, so now we kind of know how to pronounce it. What is it? Autophagy is a process that works

inside your cells, and it helps your cells replace damaged parts. And by the way, how it does this is really cool. The cell literally eats chunks of itself. In fact, that's what autophagy means in ancient Greek, self-eating. It's like the little cannibal inside us all. And the key here is that the cells can then recycle those old dud pieces to make shiny new 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 then means you'll be getting rid of more bung cell parts, creating more new parts and just generally keeping us healthy, whether that means fighting off Alzheimer's or making us live longer. Now, the big problem with these claims is that basically all of the research that these brohards are quoting comes from studies that aren't in people. First and foremost, there's never been anything showing like in humans that either calorie restriction or fasting helps people live longer. You know, those are all studies done in like worms and yeast and mice and that we're just kind of extrapolating from.

Basically, when it comes to this question of whether fasting boosts autophagy in you and me, humans that is, all we have are a handful of studies that are actually really conflicting. So some seem to show that fasting boosts autophagy and others don't. One researcher told me that part of the reason for this is that scientists don't even have a clear way to measure changes in autophagy in people. Which is all to say that the cupboard of evidence is really quite bare. And that's why you won't catch Krista

lazing about on a Sunday afternoon watching these YouTube videos. It actually just drives me nuts. I don't even watch those videos, honestly. I don't read anything about intermittent fasting online because I just get like really irritated. Conclusion. When it comes to the evidence that fasting will make you live longer, well, if you're a worm or a mouse, we've got some great news for you. Also, how are you listening to this podcast? For humans, the research just isn't there. The proof is in the pudding, which for now, I'm eating. But there is an area of fasting research that's racing ahead, and it's in cancer.

Fasting may actually weaken tumors. Researchers are looking into the benefits of starving cancer. Now, we know the idea that any diet could kill cancer, it sounds nuts. But there's actually good science as to why this might work. You see, many types of cancer love sugar. They just, like, eat it up. And this has been known for ages. But more recently, scientists have wondered,

well, if cancer loves sugar so much, and when you fast, your body kind of runs out of sugar, couldn't this cut off cancer's food supply? Walter Longo is a professor in aging at the University of Southern California, and he told us what it might be like for the 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 traditional medicine like chemotherapy, it's like a one-two

punch. So the fasting and the chemois able to search and destroy every cancer cell. I 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. So to test this, Walter gave a bunch mice cancer, in a 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.

To save the little mousies, Volta put them on a fast as well as giving them chemo. And it worked. A lot of the mice survived. And other scientists doing similar work found this too. Using that one-two punch, cancers in mice were shrinking. 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. Scientists are now researching whether fasting can help fight cancer in people. And already we have some exciting results.

In a study of more than 2,000 women who had breast cancer, those who restricted the time they were eating, which meant they were fasting for more than 13 hours each day, they were less likely to get breast cancer a second time. And more and more trials will be coming out, testing different kinds of fasting diets. Walter is involved in a few of them, and he's taken a sneak peek at the results.

And what are these studies finding? That I cannot tell you. Oh! Are they positive? Let's say that I can say that they're definitely not negative. Definitely not negative. That's all I can say. I'm very excited. Yeah, let's say that everything I've seen is really, really impressive. Volta expects the results of these trials to be out in the next few years. And while Volta is excited, he's not getting carried away. There have been lots of promising cancer treatments in the past, and yet we still don't have a cure.

It's a humbling experience, and so there is a lot of uncertainties. It's going to be interesting to see what happens. One of the uncertainties with cancer patients is that some fasting diets might cause other problems, like people might lose too much weight and become malnourished. And away from cancer, this got us thinking, are there other side effects to these fasting diets, like other than losing the joy of eating? Well, some people do report feeling constipated, dizzy or weak. And then there's one 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 and they 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 kind of surprising side effects that are why people should be cautious when they're diving into these fasting diets, particularly some of the more extreme versions. So when it comes to fasting, does it stack up like pancakes with maple syrup? One, will you lose weight? Yes, 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? Well, there's some exciting worm research, even mouse research. But no good evidence for this in humans. And three, can fasting fight cancer?

Well, the most promising research is in fasting combined with chemotherapy. And things are looking good for now, but we need more published work. We'll know more in the next few years. So, what are we to make of these fasting diets? Is this a wonder diet or a wonder-why-your-friends-are-on-it diet? Well, it's a little bit of both. There is some interesting work happening here, but the brohards and the health fluences,

they're getting a bit carried away. For me, I'm not seeing enough research to change my diet. But Katie? Hello. You're still on the diet. Yeah, I am. Are you going to stick with it? Yeah, I am.

Really? Yeah. You don't have to. We're almost finished the episode. I know, but I like it. Really? I know, I am. Really? Yeah. You don't have to. We're almost finished the episode. I know, but I like it. Really? I know. I know.

I think I like it because I'm pretty snacky. Like my mum would probably call me a bottomless pit. Thanks, mum. Thanks, mum. So having boundaries around when I can and can't eat I think is helpful. I don't feel as heavy, which is nice. That's science versus fasting. And Katie.

Hey. So how many citations in this week's episode? 125. Oh, my goodness. And if you would like to see pics of me wearing a space helmet, they're on the Instagram page. And what's our fancy new Instagram page? Science underscore VS.

It's quite appropriate. Yeah. Given that's our name. Nailed it. This episode was produced by our senior producer, Caitlin Sorey, and me, Wendy Zuckerman, with help from Michelle Dang, Rose Rimler and Meryl Horn. We're edited by Blythe Terrell,

with extra editing help from Caitlin Kenny and Annie Rose Strasser. Fact-checking by Eva Dasher and Michelle Dang. Mix and sound design by Peter Leonard. Music by Peter Leonard, Emma Munger 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-Vendelboe, Dr Chiang Liu, Dr Dorothy Sears, Professor Mark Mattson, Dr James D. Dvorak, Dr Calloway Scott,

Professor Richard Billows, Professor Nancy Warman, Dr Barbara Kowalsik and the University of Alabama in Birmingham. Also, thanks to Kimmy Regler, Helen Zaltzman, the Zuckerman family, Frank Lopez and Joseph Lavelle-Wilson. Next week, we're tackling emotional support animals, bringing pets on planes. Is there any evidence that this is a good idea? Ow, ow, ow.

Why would you do that, Hal? Why would you do that? It's science. What kind of question is that from you of all people? I'm Wendy Zuckerman. Back to you next time.