Weight Loss: Why Won't It Stick?

If you have ever tried to lose weight only to find the weight crept back on, you’re not alone. In fact, for tons of people, this happens over and over again. This is called “weight cycling,” and a bunch of influencers are saying that this is terrible for us. They say that it can ruin your metabolism forever and that it can lead to stuff like diabetes and scary muscle loss. So could that be true?? And why does this happen at all? We find out with nutritionist Prof. Faidon Magkos, immunologist Prof. Alyssa Hasty, and health policy researcher Dr. Jamie Hartmann-Boyce. Note: In this episode we discuss weight and weight loss. Please take care when listening, and here are some resources: National Association of Anorexia Nervosa and Associated Disorders (ANAD) helpline: 1(888)-375-7767 Crisis support: United States: US National Suicide Prevention Lifeline Dial 988 (Online chat available); https://www.crisistextline.org/text-us/ Text “HOME” to 741741 Australia: Lifeline 13 11 14 (Online chat available) Canada: Call or text 988 United Kingdom: Samaritans 116 123 (UK and ROI) Full list of international hotlines here Other help available: spotify.com/resources Find our transcript here: https://tinyurl.com/ScienceVsWeightCycling In this episode, we cover: (00:00) What we’re hearing about weight cycling (07:14) Why is it so hard to keep the weight off? (12:45) Does weight cycling break your metabolism? (18:58) Will you gain fat and lose muscle? (23:17) Weight cycling and inflammation? (28:35) Will weight cycling make you sick? This episode was produced by Rose Rimler, with help from Ekedi Fausther-Keeys, Meryl Horn, and Michelle Dang. Wendy Zukerman is our executive producer. We’re edited by Blythe Terrell. Fact checking by Diane Kelly. Mix and sound design by Bobby Lord. Music written by Bobby Lord, Bumi Hidaka, So Wylie, Emma Munger and Peter Leonard. Thanks so much to all the experts we spoke with for this episode, including Dr. Heidi Silver and Dr. Andrea Rossi. Special thanks to Jennifer C. Wolfe and Sasha Borissenko. And big big thanks to all the folks who called in to tell us about their weight cycling experiences. 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. Follow Wendy on TikTok @wendyzuk Science Vs on Youtube @ScienceVsPodcast Science Vs on Instagram @science_vs Learn more about your ad choices. Visit podcastchoices.com/adchoices

• 0:00Speaker 00

  Wow, wow, wow. So it's real, it is true. It is true that weight cycling can mess up your metabolism. Not so fast. Hi, I'm Wendy Zukerman and this is Science Versus.

• 0:18Speaker 00

  Today on the show, why is it so hard to lose weight and keep it off? Plus, what happens to your body when you lose a bunch of weight, put it back on, and lose a bunch of weight and put it back on? Because the internet is saying that this cycle, which is very common, is actually really, really bad for your health. But is it true? And just quickly, before we get started, I do want to say that if this is a sensitive topic for you, please take care while you're listening to the show and we're going to put some resources in our show notes. Okay, to get into the science here, we have senior producer Rose Rimla. Hello, Rose.

• 0:56Speaker 01

  Hi, Wendy.

• 0:57Speaker 00

  Where do we begin?

• 0:58Speaker 01

  The first thing I want to do is I want to introduce you to someone I recently talked about this quite a, quite a bit with. His name is John Rossi. He's a musician, he's actually a drummer. I called him up because he is someone who has struggled a lot with his weight.

• 1:11Speaker 02

  I have been weight cycling most of my adult life and it's not fun.

• 1:18Speaker 00

  Weight cycling. So this is the term for when folks lose a bunch of weight, put it back on, lose a bunch of weight, put it back on, right? Is this, this is the new internet term that I guess in the nineties we were calling yo-yo dieting?

• 1:33Speaker 01

  Yeah, I think so. I think weight cycling is like a little bit more, sounds a little more scientific or something. And so John's story is that he initially lost a lot of weight in his twenties. That was like the first time he ever lost weight. He lost quite a bit of weight and his appearance really changed. People, he said, were complimenting him a lot. He was getting a lot of positive attention. And it changed a lot of things for him. He said it changed the way that he dressed. So he said that before this happened, he was wearing like dark t-shirts and baggy jeans.

• 2:06Speaker 02

  And now I was wearing the most like funky, pink, cool stuff and skinny jeans and, and I was, I was in it to win it.

• 2:15Speaker 01

  What was your wackiest outfit from that time?

• 2:17Speaker 02

  I had, um, so I had a pink t-shirt that I like to wear with a pink like flannel over shirt, like a button down over it, unbuttoned with matching pink sunglasses.

• 2:29Speaker 01

  That sounds pretty rad.

• 2:30Speaker 02

  It was, it was so bright and it was so good and I, I, I miss it.

• 2:36Speaker 01

  He eventually gained back a lot of the weight that he had lost and so he put his pink outfit in the basement. So that was the first time. But he's since then gone through a bunch of these cycles, losing weight, gaining back weight, losing weight, gaining back weight. And he's not alone. Studies find that up to half of adults in the US have gone through at least one weight cycle.

• 2:57Speaker 00

  Half of, of all adults in the US have experienced this.

• 3:01Speaker 01

  Yeah, it's very common and it's also very common for it to happen repeatedly. So another survey found that of people who do weight cycle, they go through on average eight cycles by the time they're middle aged. And you know, he's right on track for that average.

• 3:15Speaker 02

  I am currently on my ninth time trying to lose weight.

• 3:18Speaker 01

  Wow.

• 3:19Speaker 02

  Counting that first one.

• 3:20Speaker 01

  How many pounds do you think that is over the course of your life?

• 3:24Speaker 02

  I mean, if I had lost all of this together, I'd, I'd be in the negatives.

• 3:28Speaker 01

  Yeah, you like lost your entire self.

• 3:30Speaker 02

  Yeah, yeah, yeah. Like I have lost multiple people, you know, over this, this time period.

• 3:36Speaker 01

  In fact, he says he's lost and put on hundreds of pounds over the last couple of decades.

• 3:41Speaker 00

  Yeah.

• 3:42Speaker 01

  You know, John has worked so hard so many times that when this happens, it just feels awful for him.

• 3:49Speaker 02

  Terrible, like truly, like I was failing myself and I was, I was, you know, I had succeeded at something and then failed at it, which I think is probably worse than just never succeeding at something. And, um, it's really hard. It is. I would take every other challenge in my life and double them if I could get rid of this one.

• 4:16Speaker 01

  Yeah, I heard similar things from other people who I spoke to for this episode. Listeners called in and just seemed like there is a really common theme of frustration, sadness, and then also a lot of self-blame.

• 4:29Speaker 03

  Ugh, you know, I've done it again. I just couldn't help myself or I wasn't paying attention or I wasn't doing what I was supposed to be doing. I don't know how to get out of this cycle.

• 4:44Speaker 04

  When I was with a bunch of friends and had to climb on a scale in front of a bunch of people to be weighed to see if I could ride a ride at a carnival and my weight was right back up to where it had been, over where it had been before I started Weight Watchers, three years before, I was devastated and went into a depression spiral that lasted for years.

• 5:15Speaker 01

  Oh, so people really want to know more about why this happens to them. And in this episode, we are going to get into that.

• 5:22Speaker 00

  Yeah.

• 5:23Speaker 01

  But we're going to get into more because beyond sucking, which it clearly does.

• 5:27Speaker 00

  Yeah.

• 5:28Speaker 01

  Now there's a lot of internet claims that say that this is actually bad for your health.

• 5:33Speaker 00

  Cue the influences, Rose.

• 5:36Speaker 01

  Yo-yo dieting is so bad for us. Not enough people are talking about how damaging repeated weight loss and regain can be. It wreaks havoc on our body's internal processes and the infrastructure that keeps us alive. Yo-yo dieting is killing you.

• 5:53Speaker 01

  And specifically what people talk about is that you're like ruining your metabolism.

• 5:57Speaker 00

  Right.

• 5:58Speaker 01

  That you're going to end up with a higher body fat percentage and less muscle than you would have otherwise. And that you're just, you're going to be sick. You're going to get diseases like type 2 diabetes, heart disease, that kind of thing.

• 6:10Speaker 00

  And you would have been better off if you just never, never tried at all. Kind of the implication.

• 6:15Speaker 01

  Yeah, some people say that. So we're going to get into all of that. We're going to do that for John too. John is a very sciencey person, but he says this one, this is kind of hard for him to dig into.

• 6:27Speaker 02

  This one's too close to home. I've read so many things, I've heard so many things. I just want to hear from people that I trust, like a true scientific look at all of this. Because I can't, I, I can't at this point.

• 6:42Speaker 00

  I really felt like, duh, duh, duh, duh, duh. Rose!

• 6:47Speaker 01

  You've got your cape?

• 6:48Speaker 00

  You're a voice we trust.

• 6:50Speaker 01

  Oh, I have my cape, it's my cape actually.

• 6:52Speaker 00

  Yeah, yeah, yeah, yeah, yeah. I'm just in costume.

• 6:54Speaker 01

  I'll be the voice.

• 6:55Speaker 00

  Yes. The science on weight cycling and is it really killing you? Coming up after the break.

• 7:07Speaker 05

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• 8:38Speaker 06

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• 9:09Speaker 07

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• 9:45Speaker 00

  Welcome back. Let's find out why it's so hard to lose weight and then keep it off. Because it's because everything's political these days. It actually almost feels like the woke thing to say is it's so hard to lose weight and keep it off. And the people who say it like it is, they'll tell you if you diet and keep that diet, you can lose weight, you know. So is it, is this just wokeness and unawokeness gone mad? Or give me some actual data here.

• 10:21Speaker 01

  I mean, if it were that easy, we wouldn't have things like the National Weight Control Registry, which is set up to specifically find people who can lose a lot of weight and keep it off, and track them and study them.

• 10:35Speaker 00

  Mm hmm.

• 10:36Speaker 01

  That's how rare it is to lose a significant amount of weight and keep it off for longer than like a year.

• 10:42Speaker 00

  Right.

• 10:42Speaker 01

  And one person I spoke with, Elena, she's an actor from New York. She had heard about this registry.

• 10:48Speaker 03

  That was like my goal was like, I want to be in the registry.

• 10:55Speaker 03

  So I guess like, you know, if people do lose a bunch of weight and keep it off long term, is there anything like why? What's special about them? What's special about them? Are they addicted to exercise and psychotic about what they eat? And that's the only way you can do it?

• 11:16Speaker 00

  Great question, Elena. What's happening? Is that, is that what's special about them?

• 11:22Speaker 01

  Yeah, well, the scientists behind the registry have shared some things that these people seem to have in common. Some of them are kind of random, like they tend to eat breakfast.

• 11:30Speaker 00

  Oh.

• 11:31Speaker 01

  So take with that what you will.

• 11:32Speaker 00

  Okay.

• 11:35Speaker 01

  They also exercise a lot, on average, an hour a day, these folks.

• 11:39Speaker 00

  An hour a day? Yeah, that's committed.

• 11:42Speaker 01

  Yeah, and to Elena's point, like, are they, I think she said psychotic about what they eat? I don't know if they're psychotic about it, but they're very careful.

• 11:49Speaker 00

  Uh huh.

• 11:50Speaker 01

  The researchers said that they exhibit, quote, "a high level of dietary restraint."

• 11:55Speaker 00

  Mm hmm. So it really becomes their whole life?

• 11:59Speaker 01

  It has to become very important, yeah.

• 12:02Speaker 00

  Okay, so then why is it?

• 12:05Speaker 01

  Why does it take so much restraint?

• 12:07Speaker 00

  Why does it take so much? That's right.

• 12:09Speaker 01

  Yeah, so there's a few reasons. Um, one is that when you lose weight, your hormones change. Your hunger hormones increase and your fullness hormones decrease.

• 12:19Speaker 00

  So if you, to this point of if you just stayed eating a certain number of calories that allowed you to lose weight in the first place? If you just stayed on that diet forever, you could keep this weight down. Actually staying on that diet forever becomes harder and harder.

• 12:36Speaker 01

  Yes, it becomes harder and harder because your body is nudging you towards eating more to counteract that weight loss.

• 12:42Speaker 00

  Mm hmm.

• 12:43Speaker 01

  And there's a really cool study I want to tell you about that shows this.

• 12:46Speaker 00

  Mm hmm.

• 12:47Speaker 01

  And shows just how like below conscious awareness this is happening.

• 12:50Speaker 00

  Yeah.

• 12:51Speaker 01

  So in this study, researchers gave people a drug that pulls sugar out of your body and into your urine. So you end up peeing out a lot of sugar.

• 13:01Speaker 00

  Mm hmm.

• 13:01Speaker 01

  This is in the diabetes world, this drug.

• 13:03Speaker 00

  Okay.

• 13:04Speaker 01

  Because you're, you're peeing out a lot of sugar, you lose weight. You're like excreting calories.

• 13:09Speaker 00

  Mm hmm.

• 13:09Speaker 01

  So people on this drug tend to lose weight.

• 13:11Speaker 00

  If you tasted your urine, it would be sweet?

• 13:15Speaker 01

  Mm, yes.

• 13:16Speaker 00

  Okay.

• 13:19Speaker 01

  You know, if you, if you run out of honey, you know? It's good to have a little backup.

• 13:24Speaker 01

  This was a controlled study. They also had people take a placebo pill.

• 13:27Speaker 00

  Mm hmm.

• 13:28Speaker 01

  They had another group on a placebo pill. So if you were in the study, you didn't know if you were given a pill that was causing you to excrete more calories or not.

• 13:36Speaker 00

  Okay, uh huh.

• 13:38Speaker 01

  Then they followed people to see kind of like how they ate after that. And they found that the people on the drug, without knowing that they were losing weight, started to eat more.

• 13:47Speaker 00

  Mm hmm.

• 13:48Speaker 01

  The people on the placebo drug, no, there wasn't that kind of change.

• 13:52Speaker 00

  Mm, right.

• 13:55Speaker 01

  So just like.

• 13:56Speaker 00

  Those hunger hormones kicking in, they were just a little bit more hungry?

• 14:01Speaker 01

  Just a little bit, yeah, but it adds up.

• 14:02Speaker 00

  So this is one reason why it's so hard. Your body wants to conserve calories, which for most of human history, we were hunting for food. Food was hard to get and that's how humans evolved. And now it's very different. So it makes, it does make perfect sense that there are these things beyond our control in our body that are pushing us towards weight gain rather than weight loss.

• 14:27Speaker 01

  And I think this is why it's so confusing and frustrating for people because they're still eating below what they want to eat. They're still like restricting their dietary intake. I heard someone give a talk where they said, um, keeping off weight is like holding a rubber band really tight. So you have to keep holding it and it's very hard to do that. Eventually you relax a little bit.

• 14:51Speaker 00

  Mm hmm.

• 14:51Speaker 01

  And another thing that people bring up is about metabolism. This idea that your metabolism changes from weight loss and that's another factor.

• 15:01Speaker 00

  That's right, because people, the people who say that weight cycling is dangerous, wasn't, one of their arguments was that it actually breaks your metabolism in the end, right?

• 15:11Speaker 01

  Right.

• 15:11Speaker 00

  Therefore making it even more difficult to lose weight.

• 15:15Speaker 01

  Yeah, so let's, so let's dive into metabolism.

• 15:17Speaker 00

  Yeah.

• 15:17Speaker 01

  I talked about this with Fathan Magkos. He's a professor in the Nutrition and Exercise Department at the University of Copenhagen. And the first thing he told me was that yes, your metabolism will get slower when you lose weight.

• 15:30Speaker 00

  Mm hmm.

• 15:31Speaker 08

  When people lose weight, they burn fewer calories. And this happens both at rest and during exercise. And that is completely normal because a smaller body actually needs fewer calories to sustain its function.

• 15:44Speaker 00

  So it is true. It is true. As you get smaller, your metabolism does slow down.

• 15:50Speaker 01

  Yes. It's so basically what our metabolism is mostly doing is running a complicated machine. The size of that machine matters. If you're a bigger machine, you need more energy, you need more calories. If you're a smaller machine, fewer calories, less energy. And so as people lose weight, they have a smaller machine to run and they need fewer calories. And that in itself could be challenging to sort of dial down your calories more and more.

• 16:13Speaker 00

  All right. So then can we take it one step further? Because the internet always does.

• 16:19Speaker 01

  Yeah.

• 16:20Speaker 00

  If you then weight cycle, does over time that process break that machine of ours? And, and ultimately break your metabolism in some way?

• 16:30Speaker 01

  Um, so the, the people who talk about this, they often talk about this one particular study.

• 16:36Speaker 09

  Let's talk about the Biggest Loser study. The Biggest Loser study? It's the Biggest Loser study.

• 16:42Speaker 01

  The Biggest Loser. Remember that, Wendy?

• 16:44Speaker 00

  The reality show?

• 16:45Speaker 01

  Yep, the reality weight loss competition.

• 16:47Speaker 00

  Uh huh. Yes, of course I remember it. Yelling, lots of yelling at people.

• 16:51Speaker 01

  Lots of yelling.

• 16:52Speaker 03

  Dan, no! I can't. Yes, you can! Get back to work. Come on! Dana, come back, Dana. You're acting pathetic.

• 17:01Speaker 01

  It was really intense. It had people do hours of exercise a day, like two or three hours a day, while they were cutting calories as well significantly.

• 17:09Speaker 00

  It was mad. It was mad when you think about that moment in history. And then, and then everyone would go for the, for the weight, where they would measure themselves and everyone would line up.

• 17:19Speaker 01

  The public weigh-in.

• 17:20Speaker 00

  The public weigh-in. It was just so medieval. And it was just, wow, wow. Okay, we were doing that. Why are we talking about it on Science vs.?

• 17:32Speaker 01

  Because one good thing, interesting thing came out of that show. Science, we have some science from that show.

• 17:39Speaker 00

  Uh huh.

• 17:39Speaker 01

  Because one season, scientists actually followed contestants before and after they were on the show, measuring their resting metabolic rate. So they did that before they started the show, before they lost weight.

• 17:51Speaker 00

  Yeah.

• 17:51Speaker 01

  And then after the show, when they had lost weight. And they lost a lot of weight. On average, this group of people, it was like 16 people. Um, they lost about a third of their body weight on average.

• 18:00Speaker 00

  Wow. And so did their metabolism slow down as expected?

• 18:06Speaker 01

  So it slowed down, of course, because they're smaller.

• 18:09Speaker 00

  Machines were smaller. But then the question is when they, they put the weight back on, did they? What happened next?

• 18:17Speaker 01

  They did. Um, so over the course of six years, they, um, most people put some of the weight back on or all of it back on. And the scientists circled back. They got back to them after these six years and they measured their resting metabolism again.

• 18:33Speaker 00

  Mm.

• 18:35Speaker 01

  And so you would expect if the weight had come back, then the metabolism would bump up as well, right?

• 18:41Speaker 00

  That's right. So what happened?

• 18:43Speaker 01

  They didn't find that.

• 18:46Speaker 01

  These folks, their metabolism on average was still suppressed years later.

• 18:51Speaker 00

  By how much?

• 18:53Speaker 01

  Uh, well, here's Fathan.

• 18:54Speaker 08

  So their resting metabolic rate was lower than predicted by about 500 calories per day.

• 19:02Speaker 00

  What is that in food?

• 19:04Speaker 01

  It's a, it's a Big Mac.

• 19:05Speaker 00

  Okay. Wow, a Big Mac a day? That's how much their metabolism had dropped on average.

• 19:14Speaker 01

  Right, meaning like next to someone who hadn't had this experience but was sort of the same size.

• 19:20Speaker 00

  Yeah.

• 19:20Speaker 01

  That other person could eat a whole extra meal, essentially.

• 19:23Speaker 00

  Yeah.

• 19:24Speaker 01

  Per day than they could to stay the same weight.

• 19:26Speaker 00

  It is true. It is true that weight cycling can mess up your metabolism.

• 19:31Speaker 01

  Not so fast.

• 19:32Speaker 00

  Okay.

• 19:34Speaker 01

  This is a weird study.

• 19:34Speaker 00

  Hmm.

• 19:36Speaker 01

  It's small. What people did is quite extreme. We have other studies. Um, that are a little bit more in keeping with the reality of what happens to most people. And bigger, more people in the studies.

• 19:50Speaker 00

  Great. Yes, this was just 16 people, right? Okay, so what else, what do other studies show?

• 19:55Speaker 01

  Some studies do also find some, some effects, some like suppression of the metabolism.

• 20:00Speaker 00

  It's not just the biggest loser. Okay, right?

• 20:02Speaker 01

  But the biggest loser found the biggest, most extreme results.

• 20:06Speaker 00

  Hmm.

• 20:06Speaker 01

  Um, most of the studies find something much smaller. And in fact, a meta-analysis found it was, it was quite a small amount on average.

• 20:15Speaker 00

  The metabolism lowered by a small amount on average.

• 20:19Speaker 01

  Yeah.

• 20:19Speaker 00

  Uh huh.

• 20:20Speaker 01

  And it's actually so small that Faden argues that it actually could be within the margin of error for what these measurements can actually, um, detect.

• 20:29Speaker 00

  Uh huh. So this is good news for John, who's been weight cycling nine times, right? It suggests he, he hasn't broken his metabolism, right?

• 20:40Speaker 01

  Yeah, yeah. And I, I called him actually, and I, after we talked the first time, after I'd done some research, I called him back and I told him about some of the science here, including this metabolism finding.

• 20:49Speaker 02

  I've been told by so many people my whole life that I, you know, that I am hurting myself and I am, am causing myself these like long-term issues and.

• 21:01Speaker 01

  From the weight going up and down?

• 21:03Speaker 02

  Yeah, yeah, yeah. To the point where it has scared me to try losing weight sometimes. And I'm like, no, what if I'm doing more damage? Um, and so that's, that's really encouraging.

• 21:13Speaker 01

  Science to the rescue.

• 21:14Speaker 00

  Science to the rescue.

• 21:16Speaker 01

  No, we're such nerds.

• 21:17Speaker 00

  I know. It's nice, it's nice. Cause science doesn't always come to your rescue, you know?

• 21:23Speaker 01

  It does not, and sometimes it really kicks your ass. So.

• 21:27Speaker 00

  Okay. So the next thing I want us to look into is what happens to your muscles when you lose weight and then put it back on and lose weight and put it back on? Because the way some people talk about it online, it's almost as if your muscles will disintegrate over time. Do you know what I mean? This whole, the internet's so extreme. What, what is happening to your muscles?

• 21:50Speaker 01

  It's extreme. What people do say is that, um, you know, when you lose weight, you lose some of your muscle and then you, when you gain it back, you don't get the back the muscle, or not as much. You, you get back more fat.

• 22:00Speaker 00

  Okay. Yeah, yeah, yeah.

• 22:02Speaker 01

  And that can happen.

• 22:03Speaker 00

  Uh huh.

• 22:04Speaker 01

  So there is a, a study in North Carolina where researchers followed people who went through a weight cycle uh, over about a year, lost weight, gained it back. They found that people lost 74% of the weight as fat, but when they gained weight back, 88% came back as fat.

• 22:24Speaker 00

  Right. But when, it's not a huge difference, but it's definitely there, right?

• 22:28Speaker 01

  It's there. Yeah.

• 22:29Speaker 00

  It's there. And you could imagine if you have that difference over time with weight cycling, you're going through this nine times.

• 22:38Speaker 00

  The fear would be that then it would compound and you would, with every weight cycle,

• 22:45Speaker 00

  lose more and more muscle. Is that what we see?

• 22:48Speaker 01

  Well, not every study finds this. So a very similar study.

• 22:51Speaker 00

  Rose, you've done it to me again.

• 22:55Speaker 01

  Look, you gotta read more than one study and.

• 22:58Speaker 00

  You gotta tell me.

• 22:59Speaker 01

  Then you get the.

• 23:02Speaker 00

  All right. So what's your guess? Okay. Don't carry me.

• 23:06Speaker 01

  Let me tell you about this other study.

• 23:07Speaker 00

  Yeah, tell me about the other study. Great.

• 23:09Speaker 01

  This one was from Germany.

• 23:10Speaker 00

  Okay.

• 23:10Speaker 01

  Uh, researchers similarly followed people when they lost weight and gained it back.

• 23:14Speaker 00

  Uh huh.

• 23:15Speaker 01

  And they gained pretty much the same amount of fat as they had initially lost, same amount of muscle.

• 23:20Speaker 00

  Hmm.

• 23:21Speaker 01

  No real difference. So what you might ask me is the difference between those two studies?

• 23:27Speaker 00

  Yes. That is what.

• 23:29Speaker 01

  You might ask me.

• 23:29Speaker 00

  I will ask you. What is the difference between those two studies?

• 23:33Speaker 01

  Um, the difference was age. So in the study where people gained back more fat than they had lost, they were older. They were people in their 50s, 60s and 70s. While in the study where people did not really see a difference, they gained back just as much muscle as they had lost. They were younger, 20s, 30s and 40s.

• 23:51Speaker 00

  Mm hmm. And we know that over time, you, you lose muscle. We all lose muscle, whether we're going through weight cycling or not. That is just one of the ingloriousness.

• 24:01Speaker 01

  It just happens to everybody.

• 24:01Speaker 00

  Of aging. Yes. So, so this isn't such a big deal then, you think?

• 24:08Speaker 01

  I mean, it's, it's, that's, this is a tough one because, and I have spoken to some researchers who are genuinely worried about this. So that's a legitimate concern, but the way people talk about this online, that you're like doomed to ruin your body composition.

• 24:26Speaker 01

  I didn't see any evidence that that's the case.

• 24:28Speaker 00

  Right.

• 24:29Speaker 01

  But yeah, I mean, and then your question, Wendy, of like, does this compound? Like, does with each successive weight cycle, you lose more muscle, you gain more fat?

• 24:36Speaker 00

  Yes.

• 24:38Speaker 01

  I can't really answer that because we don't really have those studies. We have very few studies that follow people for more than one weight cycle. And that's true for all this. Mostly it's just one, one round of weight cycling.

• 24:47Speaker 00

  Hmm. What did John think about this?

• 24:51Speaker 01

  He, you know, John said he wasn't, this wasn't something he was actually that worried about.

• 24:55Speaker 00

  Hmm.

• 24:56Speaker 01

  Cause from his own experience, he was like, no, I, I, when I lose and gain weight, it doesn't really affect, it doesn't seem to affect the way I can operate my body. Like he, he talked about being a drummer.

• 25:06Speaker 02

  I, I trust my arms. Whatever size I am, like I trust that my muscles will do the same thing.

• 25:12Speaker 01

  Yeah.

• 25:12Speaker 02

  So that does make sense. I wasn't too worried about that, but I mean, it's nice. Like I wasn't worried about it, but, but cool. I'll take it.

• 25:21Speaker 00

  All right, Rose, after the break.

• 25:23Speaker 01

  We're gonna talk about like health more broadly, um, inflammation, diabetes, heart disease. Does weight cycling make all of that worse?

• 25:32Speaker 00

  You coming in?

• 25:41Speaker 07

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• 27:43Speaker 00

  Welcome back. Today on the show, we're talking about weight cycling or yo-yo dieting. What happens to your body when you lose a bunch of weight and put it back on, lose a bunch of weight and put it back on? The internet says that this can over time make you sicker and sicker. And we're looking into that claim. And one idea that I really want to probe is around inflammation and that this weight cycling can ultimately increase the amount of inflammation in your body.

• 28:14Speaker 00

  Tell me the science, Rose.

• 28:16Speaker 01

  This comes from what we know about fat tissue on our bodies. So you and I, Wendy, and maybe our audience probably assumes that fat, the fat on our bodies is inert. It's just like squishy stuff that's there to act as padding or maybe, you know, provide a little extra energy if we need it. And actually, that's what scientists used to think too, until like the mid 90s, when they started to realize that fat is actually a very active tissue in the body. And one of the ways it's active is that it's actually full of immune cells. I spoke about this with Alyssa Hasty. She is currently a professor

• 28:59Speaker 01

  at the University of Texas Southwestern Medical Center.

• 29:02Speaker 14

  Every single immune cell that's known to immunologists exists in our fat.

• 29:08Speaker 01

  This is especially true for the fat that collects around our organs, visceral fat, which you're probably familiar with.

• 29:15Speaker 00

  The more dangerous fat, that's the fat scientists are worried about.

• 29:20Speaker 01

  Yeah, when fat collects around your organs, that's bad. And one reason is because that's not really a place where we're meant to store fat. It's like not set up. The body isn't really set up to support the fat there. And so there isn't really like good blood supply for those cells, those fat cells in that area. And so they get stressed out. They don't get enough oxygen and they malfunction and they even die. So then there are these white blood cells called macrophages that have to go in and clean up the debris from those dead and dying cells. But then they can get overwhelmed. So here's Alyssa.

• 29:57Speaker 14

  And so they send out signals that say, hey, other immune cells, other macrophages, come help us out here. We've got to take care of this debris, this dead cell.

• 30:07Speaker 00

  Uh huh. So then you get more, basically more and more inflammatory cells, right? More and more macrophages then calling out more and more immune cells to come and help. And you just get this kind of vicious cycle. But then the question for us today is, does that get worse if you lose weight and put it back?

• 30:30Speaker 01

  Right. So that's what Alyssa wanted to test. So she set up this mouse model where she had the mice gain weight by feeding them a high-fat diet for nine weeks. Then she switched them to a low-fat diet. Was that kind of, is that like putting the mice on a crash diet?

• 30:46Speaker 14

  Yeah, it definitely is.

• 30:49Speaker 00

  And then she yelled at them like in The Biggest Loser?

• 30:52Speaker 01

  Yeah, and she made them go round and round and round in their little hamster like for hours and hours. And televised it.

• 30:58Speaker 00

  Yeah.

• 30:59Speaker 01

  So then to have them go through like a whole cycle, she had the mice, she put them back on a high-fat diet for another nine weeks. They gained weight again, checked on their immune cells. And what she found, especially regarding this type of immune cell called the T cell, was surprising.

• 31:15Speaker 14

  The T cells were elevated even further in the weight cycled compared to the obese only, despite the fact that they were the exact same weight and had the exact same visceral fat mass and total body adiposity.

• 31:32Speaker 01

  So these were even more like agitated. The mice were worse off in terms of what their T cells were doing than the mice, control mice who had never weight cycled but had been obese basically the whole time.

• 31:48Speaker 00

  Hmm, the immune cells didn't like it, the going back, the cycling. Uh huh.

• 31:56Speaker 01

  And so this is how Alyssa puts it.

• 31:58Speaker 14

  The body remembers. The immune system remembers our body weight and gains and losses in that.

• 32:07Speaker 00

  Uh huh, the body remembers. How, what's going on there?

• 32:11Speaker 01

  We don't totally understand all this. But it seems like something about this, like the stress, the weight loss, the weight gain, the weight loss, is like turning on the immune system in a way that's hard to turn off. And that could be leading to some kind of chronic inflammation, which we know is bad for us in all kinds of ways.

• 32:31Speaker 00

  Hmm, we said, science isn't always your friend.

• 32:36Speaker 01

  No.

• 32:37Speaker 00

  Do we know why this is happening? And obviously, this was just a study in mice. You're gonna now give me another study where they found something totally different?

• 32:48Speaker 01

  Um, well, I mean.

• 32:50Speaker 00

  Wayne, are you really gonna give me another study that found something different? Rise!

• 32:56Speaker 01

  Yes and no.

• 32:57Speaker 00

  You're such a science tease.

• 33:00Speaker 01

  So after looking at this study in mice, I wanted to look at studies in people.

• 33:03Speaker 00

  Thank you.

• 33:05Speaker 01

  And I did find, along these same lines, I did find studies that compare people who have weight cycled versus people who have not weight cycled, but they both started out at kind of the same weight and were similar in other ways. And what those studies often find is that the weight cyclers have worse health outcomes than those who haven't weight cycled.

• 33:25Speaker 00

  In what way?

• 33:27Speaker 01

  These studies have found a higher risk of heart failure and higher risk of death, actually, a couple of studies.

• 33:33Speaker 00

  Wow.

• 33:34Speaker 01

  So I don't want to leave things there, though. And the reason is, you know, those studies are not bad studies, but they can't answer some basic questions here. So like, they're just observing what happens between one group and another. You can't say like, weight cycling caused people to be, to die or to get heart failure.

• 33:52Speaker 00

  Got it, got it. We need a different kind of study for that, a randomized.

• 33:56Speaker 01

  Sometimes we don't have.

• 33:56Speaker 00

  Control trial.

• 33:57Speaker 01

  Anything else? Yeah, but in this case, we do. We have some randomized control trials that could help us.

• 34:01Speaker 00

  Uh huh. Tell me about it.

• 34:03Speaker 01

  So I talked about this with Jamie Hartman-Boyce. She is an associate professor of health policy and management at the University of Massachusetts Amherst. And she wrote a review paper looking at studies where people lost and then regained weight after going through what are called supervised weight loss programs.

• 34:23Speaker 15

  Eating a bit less, you're at a calorie deficit, and you're exercising more. So we're not looking at people who are like on a juice cleanse for six weeks. We're looking at people who are like eating more vegetables and moving their bodies more.

• 34:37Speaker 01

  So Jamie's question was, how does the health of these people who've lost weight in this healthy way, gained much of it back? How does it compare to people who have never lost weight, who are the control groups?

• 34:50Speaker 00

  Yeah, great.

• 34:51Speaker 15

  And one of the things we found was that even if you regained the weight back, right? So even if you started a certain weight, you did your diet and exercise program, you stopped it, you went back to your starting weight, compared to someone who had stayed at a stable weight the whole time and not done that program, you were still less likely to get type 2 diabetes.

• 35:12Speaker 01

  And it wasn't just diabetes. It was also lower cholesterol and lower blood pressure.

• 35:17Speaker 00

  Why was weight cycling healthy in this case?

• 35:21Speaker 01

  It seems like it could come down to how people lost the weight, making healthy changes, getting a little more exercise, eating more vegetables. Even if people aren't able to keep up those new habits forever, the period of time where they were doing those healthy habits, which resulted in weight loss, that's what was good for them. But these other studies, we don't know how or why they lost the weight. But, and then with the mice, you know, it was like a crash diet. This was like healthy changes resulting in weight loss.

• 35:49Speaker 00

  So is it even about the weight loss at all? Or it's just that for a portion of the study, these people were eating lots of vegetables, moving their bodies, and that's what was good for them, whether or not they lost weight or not?

• 36:05Speaker 01

  That's one, yeah, I think that's a fair interpretation. I mean, there's a lot of nuance here, but it does make sense if you think about, if you know the broader literature about weight and health. So there's a study I love. They, it's a big survey, like 12,000 people were in it. They asked about healthy habits. So like, how much fruit and veg do you eat? Do you exercise regularly, smoking, drinking?

• 36:31Speaker 00

  And these were people of all kinds of weights?

• 36:33Speaker 01

  Yes, all kinds of weights. And they tracked them over time. And what they were measuring was all-cause mortality. So like, that's the big one, like, are you more likely to die? They found that the thing that mattered the most for, you know, death was not your weight, but the healthy habits that you did. So if you were someone who, your BMI technically puts you as obese, but you have all these healthy habits, you were just as likely to not die as a person whose BMI was normal and did those healthy habits.

• 37:06Speaker 00

  What these studies are suggesting is if you're doing healthy things, that's the key.

• 37:11Speaker 01

  Yes, and you have a lot more control over that than you have of your body size. So it makes more sense to focus on that. And that's what Jamie said as well.

• 37:21Speaker 15

  So I think the data is very clear that if like what we're trying to do is improve our health and wellbeing, right? Then, you know, if we eat healthier, we exercise more, regardless of what happens to our weight, and one of those things that can happen is that we lose weight and regain it, we are doing something good for ourselves, okay? And for the people who love us, who want us to stick around for longer.

• 37:45Speaker 01

  So when I told John that it's the healthy behaviors more than the weight that really matters, this is what he said.

• 37:52Speaker 02

  Wow, that's really cool. That's great.

• 37:57Speaker 00

  Science back to being your friend.

• 38:00Speaker 01

  But it was also, there's something I think about it that was slightly annoying to John because it made him think of like all the bullshit he's had to sort through and all the people saying like, oh, if you, if your weight fluctuates a lot, you're gonna really harm your health.

• 38:13Speaker 02

  Those beliefs have been so common and so repeated over and over and over again that it shows me that, you know, people don't know what they're talking about with this stuff all the time. And it's another nice reminder to not let other people shape me in a literal sense in this case. And that I should worry more about, you know, what I think and what the science says than what people tell you, you know?

• 38:43Speaker 00

  So what does this mean for that fabulous pink outfit that John's got?

• 38:48Speaker 01

  I did ask.

• 38:49Speaker 00

  Did you?

• 38:50Speaker 01

  Yeah. You said your confident, wacky outfit was like, I think you said it was like, was it hot pink?

• 38:56Speaker 02

  Yeah. Oh, my gosh. So much hot pink.

• 38:58Speaker 01

  And skinny jeans?

• 39:00Speaker 02

  Yep.

• 39:01Speaker 01

  Reflecting on that, it strikes me as a very early 2000s outfit. So what would the, let's say you get that burst of confidence and creativity and you want to express yourself through wacky dress. What does the 2026 version of that look like?

• 39:21Speaker 02

  Well, 100% goofy animal shirts, um, always. I just, I love animals so much now. Um, and probably still skinny jeans because I don't care if they're in style or not. My butt looked great in those jeans.

• 39:33Speaker 00

  That's Science vs. Thanks, Rose. How many citations are in this week's episode?

• 39:38Speaker 01

  Um, this week, there are 66.

• 39:42Speaker 00

  66. And if people want to see them in all their glory, where can they go?

• 39:47Speaker 01

  Check out the transcripts. Find that link to the transcript in our show notes.

• 39:52Speaker 00

  Thanks, Rose.

• 39:54Speaker 01

  Thanks, Wendy.

• 39:55Speaker 00

  This episode was produced by Rose Rimla with help from Aketi Foster-Kees, Merrill Horn, and Michelle Dang. Wendy Zukerman, that's me, is our executive producer. We're edited by Blythe Terrell, fact checking by Diane Kelly, mixed sound design and video editing by Bobby Lord, music written by Bobby Lord, Bumi Hidaka, So Wiley, Emma Munga, and Peter Leonard. Thank you so much to all of the experts that we spoke to for this, including Dr. Heidi Silva and Dr. Andrea Rossi. A special thanks to Jennifer C. Wolf and Sasha Borissenko. A big, big thanks to all of the folks who called in to tell us about their weight cycling experiences. Thank you so much. It means so much to us that you trust us to tell us your stories. So thank you so much.

• 40:40Speaker 00

  Science vs. is a Spotify Studios original, so listen to us for free on Spotify or wherever you get your podcasts. We're all over it. We're on YouTube. We're on Apple. If there's podcasts there, so are we. Like and subscribe, follow, do all that stuff. And get in touch with us. We're also on TikTok and Instagram. All the ways to get in touch are in the show notes. I'm Wendy Zukerman. Back to you next time.

• 41:06Speaker 16

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• 41:38Speaker 17

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