Does Being Hungry Make You Live Longer? Calorie Restriction and Longevity
You may have heard online that calorie restriction, or intermittent fasting, or both combined actually make us live longer. But what does science have to say about this? Today, we talk to Professor John Speakman about the science of calorie restriction, health, and longevity. What does being hungry have to do with being longer?
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Guest
John Speakman is a biologist who works at both the University of Aberdeen and the Shenzhen Institutes of Advanced Technology.
Wiki | Twitter | Academic Papers
The Takeaways
Time restricted feeding is the practice of limiting the number of hours per day that you’re able to have access to food. People often call this “intermittent fasting.”
Time restricted calorie restriction is restricting the number of calories as well as the time you are eating them.
Examples of intermittent fasting include:
OMAD - Eating One Meal A Day
16-8 protocol - Eating for 8 hours a day, not eating for 16.
The hours you can eat are known as your “feeding window.”
5:14 - The reason time restricted eating causes weight loss is because it causes a calorie deficit. There is nothing particularly special about eating during a certain time of day that aids weight loss.
People are simply not familiar with eating in a restricted feeding window and therefore eat less food (at least in the beginning).
6:00 - Why is intermittent fasting appealing?
Psychologically it is more appealing to restrict the time you eat, than trying to exert cognitive restraint all day, but the effect is the same.
Over time people can adapt and increase their food intake in their short feeding window.
13:32 - No matter how long a mouse or rat is kept in a lowered weight “restricted” state, it never becomes the mouse’s new “normal.” The mouse will always take the opportunity to eat more and regain the weight.
16:20 - In studies dating back to the early 1900s, significant caloric restriction has been shown to increase lifespan in animal models.
18:04 - We have no evidence of increasing lifespan through caloric restriction in humans because these studies would be really expensive and difficult to conduct. The closest thing we have is the “CALERIE” trial.
22:30 - If we assume that restriction works the same in humans as it does in mice (which is still unproved), and you start calorically restricting for your entire adult life, you may extend your life only by about 6-7 years.
if you start in your fifties, you may extend your life by about 2 or 3 years.
26:03 - The feeling of “hunger” appears to be a key portion of the longevity effects from caloric restriction (at least in animal models).
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Juna Eddie, if there's one feeling that I tried to avoid at all costs, it's being hungry.
Eddie Oh, same. You always see me bringing my lunch, and I always have lots of snacks on me.
Juna Guys. One time I made Eddie stop at a store, literally, to get me protein bars on his way to the studio because I didn't want to be hungry while we were recording.
Eddie So Juna,did I choose good bars? I chose the ones that I like.
Juna You actually did pretty good. And he picked two bars just in case I didn't like the first one, which is so generous of him. But anyways, Eddie, are you keeping up with pop culture these days?
Eddie Oh, for sure. Yesterday I was standing at the supermarket checkout, so I can tell you from the magazines that Harry and Meghan are still on the outs. Yeah, Kate and Will are not getting divorced.
Juna Amazing.
Eddie And King Charles's former mistress, Camilla, is now queen consort.
Juna Okay, that's all really interesting. But I actually meant, did you pick up any of the fitness pop culture?
Eddie Oh, yes. Right next to the candy bars in the checkout were all the magazines and they were talking about intermittent fasting.
Juna Okay. Well, why don't we talk about that today?
Eddie The candy bars.
Juna Maybe another episode. Let's talk about the intermittent fasting today. One thing that has been very popular lately is the idea that you can increase your lifespan by eating less, intermittent fasting or some combination of the two. And we've gotten so many questions from you guys about whether or not any of this stuff is true. So today, that's what we're going to talk about.
Eddie Juna, did you eat before you got into the studio today?
Juna Don't worry, guys. I actually did make sure I ate right before this episode.
Eddie Wonderful. Then we can start.
Juna On today's episode calorie restriction, intermittent fasting and longevity. Can we actually live longer by eating less?
Eddie I'm Juna Gjada, and I'm Dr. Eddie Phillips, associate professor at Harvard Medical School.
Juna And you're listening to Food, We Need to Talk, the only podcast that has been scientifically proven to increase your lifespan without calorie restriction just by listening. So let's meet today's guest.
John Speakman My name's John Speakman. I'm from the University of Aberdeen and from the Shenzhen Institute of Advanced Technology in China.
Eddie When it comes to calorie restriction, the name pretty much says it all right.
Juna You are restricting or limiting your calories.
Eddie Sounds easy if you're like a mouse or a rat in a lab. Right. They need a certain amount of food each day to maintain their weight. Yeah. Basically, a calorie restriction protocol might be providing only three fourths of the food they normally need, or maybe even only half of the food.
Juna Okay, so you're forcing them to go on a diet?
Eddie Yeah. Now, time restricted eating is also pretty self-explanatory.
John Speakman Time restricted feeding is a way of manipulating your food intake by constraining the number of hours each day that you're able to have access to food.
Juna Colloquially, a lot of us might hear this called intermittent fasting. So when people say they're doing a68 protocol, it means they're not eating for 16 hours a day and they're eating for only eight. And obviously, there's endless amounts of protocols. You could do a 12, 12, you could do a 24. You could do a OMAD.
Eddie What on earth is OMAD? It sounds like a superhero.
Juna OMAD is one meal a day. So this is like you're waking up in the morning, going to work all day, and then you have a massive meal at dinner.
Eddie You don't eat all day.
Juna Oh, yeah. Like literally, no food.
Eddie Okay, so we have caloric restriction and time restricted eating. Yeah.
Juna And the combination of the two.
Eddie Time restricted calorie restriction. It sounds like a lot of restriction.
Juna A lot of restriction going on. This would be you're not eating enough calories.
Eddie To maintain your weight.
Juna Right. And you're also eating them in a shorter time frame. Now, I'm going to say something that might upset some of our listeners. And I know this because we get questions about this all the time, and I cannot tell you how many DMS I've gotten, basically asking us to do an episode on intermittent fasting, specifically for weight loss.
Eddie Wait, Juna, why would this upset people?
Juna Well, what I was going to say is that there's nothing magical about eating in a certain time window that causes weight loss. Now, before everyone gets really mad, I know people love intermittent fasting.
Eddie Oh, yeah. The people who are dedicated to it, they are dedicated. They become like professional spokespeople. So in our house, we usually eat on the light side like 730, 8, 9. Yeah. But when we go out with friends that are intermittently fasting, we might meet them as early as 5 p.m. just to stay within their feeding window.
Juna What's the feeding window?
Eddie Oh, so when I first heard that term, I was thinking of like the drive up McDonald's, you know, where they give you that your food through the window. Yeah. But now what it means in the intermittent fasting world, it refers to the hours when you're allowed to eat.
Juna I feeding window. My feeding window is all day. That is my eating window.
Eddie It's a large window.
Juna Right. The reason that time restricted eating, as we're now calling it, causes weight loss for so many people, at least initially, is exactly the same reason that anything else causes weight loss, and that is that it is causing a calorie deficit.
John Speakman The reason why people get weight loss is they're eating less food. And the reason they're eating less food is that they're not familiar with eating within that restricted window.
Eddie Okay. So in other words, because you're not used to eating only one meal a day, you'll eat less in that one meal than you would if you were eating over the entire day. That kind of makes sense.
Juna It's hard to eat all your food in one meal like that's Crazytown. The thing that I think makes people obsessed with time restricted eating is that for a lot of us, it's just a lot psychologically easier.
John Speakman If you say to somebody, you can only eat 1500 calories and you can eat it whenever you want. That takes a lot more kind of discipline than to say to somebody, Look, you can eat as much as you want. You've just got to squeeze it into this window. It becomes really popular because it's kind of calorie restriction through the back door. You don't feel that your calorie restricted, what you're doing is you're restricting the time that you eat. But ultimately the weight loss has to come about because of a calorie deficit. So you indirectly get a calorie deficit, although you're not objectively trying to reduce your calories.
Juna In the short term. This works great for people because it's like, woo, I'm losing weight. I only for 4 hours a day, but in those 4 hours I'm free. It's awesome.
Eddie I sense that there's a but coming.
Juna Of course there's always a coming. Because let's face it, your body isn't really, you know, dumb. So it's going to start realizing, hold on, it's only in these 4 hours that I get to eat, so I better start eating more.
John Speakman I think it's clear that people adapt over time, so initially it's a bit of a challenge to do it. But you're early, you're well motivated and you do it, you know, so so you eat less food. But I think people become adapted and they're able to then increase their food intake.
Eddie And it's not just that you start slowly eating more and more, but also as we discuss on our episode of metabolism, if you're losing weight, your metabolism is then slowing.
John Speakman As the body weight falls, their energy demands are also falling. So actually the needs for food are also coming down at the same time that they're slowly adapting to the fact they're eating in that narrow window. So weight loss tends to plateau to all these kind of protocols because energy balance is being restored. And so your energy intake is creeping up again, but your expenditure is also coming down. And so they meet somewhere in the middle and that's why the sort of weight loss stops happening.
Juna So the bottom line is, guys, time restricted eating or as we colloquially call it, intermittent fasting basically works like any other diet except for the fact that people find it easier to stick to than a lot of other diets, which might be why it's so popular.
John Speakman What is good about time restricted feeding is as a protocol it actually is easier to adhere to. So, you know, there's this saying that the diet that best is the diet that you can stick to because the biggest diet you could do is just stop yourself completely for 40 days and you would lose a ton of weight. But the possibility that you'd be able to complete that diet is pretty low. And also, it would have negative health effects on you. And I think people find it technically easier to stick to type restricted feeding, particularly time restricted late feeding because it doesn't screw your social life up.
Juna So the connection between time restricted eating and weight loss is basically just calorie restriction or dieting. But since intermittent fasting is a shortcut to this calorie restriction. Let's talk about another claim that is often made about restricting your calories, and that is that it increases your lifespan. And this goes all the way back to the beginning of the 20th century.
John Speakman In 1917, there was a paper that was in science, and it involved a very few individuals.
Eddie Whoa, whoa. What? Well, excuse me. I didn't get to cue the historical side note.
Juna Oh, my fault. Sorry. Hey, Eddie, do you want to do the honors?
Eddie And now a brief historical side note. Cue the music.
John Speakman So it was four rats, I think, that had been restricted through their entire life. And they exhibited two phenomena because they were restricted in their food intake from weaning right through to the end of their life. They exhibited two things.
Juna First of all, they didn't develop properly. And second of all, they lived a lot longer than they were supposed to.
John Speakman So for a long time after that first paper, the belief was that these two things were linked together, that it was something to do with the growth restriction that was causing the extension of the life.
Juna In other words, people thought it was the fact that they were stunted that was making them live longer. Not the fact that they didn't have enough to eat.
John Speakman So there was a lot of studies between 1917 and the 1930s where people manipulated these things when they changed the amount of protein in the diet and they changed the amount of calories in the diet. And they also let animals grow properly. And then they imposed the restriction after the animals had already grown.
Juna Basically trying to separate out the effect of the underdevelopment or the effect of the calorie restriction. And the conclusion was.
John Speakman It's the calories rather than the protein. And it's got nothing to do with the growth. It's something that happens in the on time and whether it's grown to full size already or not.
Eddie So you're saying that when the animal is calorie restricted, forcibly put on a diet, they live longer.
Juna Right.
Eddie Okay. But something's not adding up here.
Juna What's that?
Eddie Well, if we put the mice or the rats on a forced calorie deficit, they'll lose weight up to a certain point. And then they stop because as we always explain, they will now have a slower metabolism because they've gone down a few dress sizes.
Juna True.
Eddie So the number of calories that used to be a deficit for them, in other words, that caused the initial weight loss. Yeah. Is no longer causing weight loss. It's no longer calorie restriction.
Juna That's true.
Eddie Do we lower it again?
Juna I mean.
Eddie Do we have them lose even more weight? Because if we keep on doing that, yeah, eventually, yes, they will end up in rat heaven eating from the all you can eat cheese buffet, trying to make up for all this restriction.
Juna So that's actually a really good point, Eddie. You're totally right. In these studies, they don't keep adjusting it down because obviously the mouse or the rat would die, as you said. But eventually the mouse does come into balance.
John Speakman In the mouse, for example, it takes about 30, 40 days for them. If you put them on 25% restriction, a 40% restriction. It doesn't seem to depend on the level of restriction, and it still takes 30 to 40 days for them to come back into balance.
Juna In other words, in 30 to 40 days, they just stop losing weight. They're back in energy balance.
John Speakman But then they're not restricted anymore. They're in balance. So the restriction is only like a nominal restriction compared to what they were previously eating.
Juna The question is, if they're not being restricted anymore and they're eating the amount they need to maintain their new, smaller body.
Eddie They're in balance.
Juna They're in balance. Why is there still a benefit to eating at that lower amount? Because they're in balance. So the restriction is like supposedly this new normal, like they're not losing weight anymore. And what's clear in this research, though, is that it's not really ever a new normal.
John Speakman It's really clear that that state is a state that the mouse doesn't want to be in. So we know that because, you know, let's say you keep a mouse in that situation where it's on 40% restriction and you keep it in that state for, say, 100 days, that never becomes the new normal. So it doesn't matter how long you keep them in that state. If you give them the opportunity to go back and eat to what they were eating before, they always take that opportunity.
Eddie Okay. So what these experiments show is that even if these mice are put on a diet, so to speak, for hundreds of days, they do not want to be there. And they will take any opportunity possible to eat normally again. Juna Isn't that what most people do?
Juna Exact. I was just going to say this reminds me so much of all the literature on weight loss and weight loss management like maintenance after.
Eddie I mean, it's like what 95% of people regain the weight.
Juna Like, I think in the last meta analysis, it's at 80%. But yes, it's pretty bad. Like people have a lot of trouble maintaining lost weight. And it's probably because just like in these experiments, we see that like your body does not want you to stay in this lowered weight state or this calorie restricted state for a really long time.
Eddie So we should say that you really cannot extrapolate data from the mice or the rats to humans.
Juna Yeah.
John Speakman I don't know that we have any studies where humans have adjusted body weight for a long period of time, like ten years at 20 years, and then given the opportunity to come back out once they're imbalanced. So this is maybe one of the limitations of doing animal studies that we don't really know whether that translates from what happens in the mouse to what happens in a human, because we just can't study humans for 20 years on their diet.
Juna I mean, the biggest difference between mice and humans is that mice are being forced to go on this diet. Right. So humans, in the context we're talking about, are choosing it. They're constantly surrounded by the possibility of being able to eat food and they're choosing not to eat it.
Eddie Are you saying a mouse would never refuse seconds of cheese to watch his or her figure?
Juna I would bet all my life savings, which isn't that much that a mouse would not refuse cheese. But it's exactly that fact that humans are using cognitive restraint. That means we're not just a product of our biology.
John Speakman Look at what the consequences of the restriction are, both in positive and negative terms. But the way that restrictions imposed is fundamentally different in the mouse than it is in the human. And that may mean that the translation in some aspects is not complete.
Juna Okay, so now let's get back to this whole living longer thing.
Eddie Yeah. How much longer we actually talking about here?
Juna Okay, so I had to dig up the study from 1917, which was a literal hassle, a hassle and a half. And keep in mind, these lab rats, less than a third of them even lived to beyond two years old.
Eddie And before we go on, I just want to say that you can more easily find the study on our website in the show notes at foodweneedtotalk.com. Yes. Okay. So they live to two years, huh?
Juna Okay. The longest living rat without the calorie restriction, it went to 34 months. Okay. So just under three years.
Eddie Okay.
Juna But when they were placed on this calorie restriction for their whole lives, they were living sometimes up to 40 months or longer.
Eddie That is a significant life extension.
Juna I mean, for reference. Okay. They said a 36 month old rat is like the equivalent of a 90 year old human and they were going from the longest rat was 34. They were going to like 40. So it's like a huge amount.
Eddie Okay. So is this how we're going to live to 120? Because if so, I'm going to need to start making some arrangements. I have so much more time than I thought I did.
Juna Okay. Well, not so fast. We're going to talk about exactly what this means for humans and your life plan right after this break.
Eddie And we're back and we're making plans for my 120th birthday party.
Juna Okay? Not quite, because, Eddie, I'm sorry to deliver the bad news. I think that we're going to find we probably shouldn't just start calorie restricting for the next 50,000 years. So first, let's talk about the fact that this model has never actually been proven in humans.
Eddie Wait, what? So all these people online are talking about increasing longevity, and this is based only on animal studies.
Juna Are we even shocked?
John Speakman So what has been done is a shorter term calorie restriction trial. So this was the calorie trial that ran for about ten years from round about 2000 through to 2012. And so what they did was they tried to get 20% restriction, I think, but they ended up only with about 15. And they then collected lots and lots of samples from these people after two years of restriction. And they had a really nice sample size of individuals that had been randomized into restriction or not restriction.
Eddie Well, this sounds like exactly the kind of experiments we want to do Right?
Juna Okay. But the problem is to find out whether or not these people live longer. You have to run the study for a long time and you have to wait for, you know, a bunch of them to die.
Eddie Or.
Juna Pass away yea. So instead, the researchers looked at biomarkers. Eddie, do you want to define what biomarkers are?
Eddie Sure. A biomarker is something we could measure in an organism that is an indicator of some phenomenon taking place.
Juna Amazing.
Eddie You want that in English now?
Juna Please.
Eddie So put simply, a biomarker could be something as simple as measuring your blood pressure or your pulse or doing some blood work to screen for cancer.
Juna Okay. Yes. So in these rat experiments, the rats were actually living longer, but they also had all of these biological changes that were correlated with them living longer.
John Speakman Body composition. So what your body fat level is. And then there are a lot of biochemical markers that you can measure. And one of those, for example, is oxidative damage. What's become super popular recently is these kind of epigenetic clock markers, which seem to be related to how long individuals live. So you have like a clock age as well as a chronological age. And the the idea is that going on these interventions slows down your biological clock, even though the chronological clock is still running.
Juna And these types of measurements were actually the ones that we can make in this calorie trial. By the way, calorie is spelled calerie.
Eddie So just a note to listeners. We have already mentioned several studies. Please go to food. We need to talk tor.com to find the articles. So in the calerie trial, we saw evidence of these biomarkers which we also saw in the mice, but we still don't actually know if the people are going to live any longer.
John Speakman Yeah, absolutely. So we don't you know, it's a matter of faith whether this is actually going to make any difference. And, you know, a really important thing to think about is how much extra life are you going to get if you do that?
Juna I mean, remember those rats that were living too, like the rat equivalent of 100 something? They were being starved from rat childhood, so much so that they weren't even developing properly.
John Speakman If you take an animal that's six weeks old and you put it on restriction for its entire life, there's a a linear relationship between the extent of restriction and the extent of lifespan extension.
Eddie So a linear relationship, the more they're restricted, the longer they live.
Juna Right.
John Speakman What you have to think about is what happens if you start it later? What happens if you institute the restriction when you're 50? Or 60. So I did a bit of modeling and a paper a while back to kind of use the animal model data to say, okay, let's just assume for the sake of argument that this works in humans exactly the same way that it does in mice, that that's the best case scenario. And then say, okay, how much benefit would I get if I stopped restriction at age 20 or 30 or 40 or whatever?
Juna So do you want to guess in the best case scenario, let's say this was exactly the same way in humans as it does in mice. How much longer do you think you live if you started restricting calories in your twenties?
Eddie 15 years.
Juna Try again. Lower.
Eddie Ten years.
Juna Try again.
Eddie Lower five years.
Juna Pretty close. It's about six or seven years. If you start restricting for basically your entire adult life, if you started later than that.
John Speakman If you're only starting your fifties, your expected lifespan is 78. So you would be on restriction for 28 years and you would maybe get an extra two years, you know, so that that's a massive amount of restraint and trouble in your life just to get an extra couple of years of life. That would also, incidentally, be massively constrained and, you know, not eating much food.
Eddie So it's only two years, but it's going to seem a lot longer than that.
Juna It's going to seem like a million years long because you're like, you can't eat anything. So it's not that surprising that even Professor Speakman, who studies this stuff, does not engage in calorie restriction.
John Speakman Absolutely not. I'm 63. If I went on to restriction today, I might spend 15 years on restriction. To my expected age of 78 and get nothing. You know, you may as well enjoy yourself and just live to be 78. You know, even if it works, just like it does in the mice, it's not going to give us the sort of these massive benefits that people have been talking about, about extending a life out to 120 or whatever.
Juna And we should also talk about the fact that these mice are in a very protected environment. So they're completely protected from getting sick, from getting infections. And that's certainly not the type of environment that we live in.
John Speakman You know, it may be that we would go on restriction and okay, we would get all the markers that you expect in the epigenetics and the free radical damage and all that sort of stuff and telomere shortening. But we would be much more susceptible to infections. And so then, you know, that might all be negated if you then die because you got a severe parasite infection or something that you would normally survive.
Eddie You know, we have not talked about exercise a lot in this episode, but we are taking a lot of leaps of faith over what he's describing.
Juna Yeah, a lot. So are you ready for the cool part?
Eddie Always.
Juna Okay. Well, Professor Speakman and his colleagues were interested in finding out what exactly about this restriction is causing an increased lifespan.
Eddie And I'm guessing that's not the easiest thing to do.
Juna It's not super easy, but let me tell you how they did it. So you remember how he said that the restriction scales linearly with the life span increase, right? Yes. So 40% restriction. So cutting back almost half your food. Yeah. Leads to double the life span extension of 20% restriction.
Eddie Right. Okay. So more restricted, longer life. Right.
Juna So they were looking for biomarkers that also scaled in a similar ish way.
Eddie So we don't have to wait for the subjects to die.
Juna Right. Exactly. And when they were looking at all these, they saw some biomarkers would stay the same, whether you did 40, whether you did 20. So they're like, okay, it can't be. Those are the real thing. But one thing that they discovered seemed to be really important was the experience of hunger.
John Speakman A couple of genes in your brain, MPY and HERP that create this state? That's what tells the animal you're in a restricted state and that then enables all these other things to happen down straight. And we know that that's pretty important because if you knock out one of these genes, then you get no effect of calorie restriction on lifespan. So it's clear that those genes that are involved in signaling hunger are a vital component of the whole effect.
Eddie Juna I got to get this straight.
Juna Yeah, yeah, yeah.
Eddie You've got to feel hungry for this to work.
Juna Yeah. So they'll calorie restrict these mice. Yeah, but they'll take out this gene that makes them feel hungry. So they're still eating way less. They just don't feel hungry and they do not live longer, even though they're eating less. So basically being hungry really sucks, but it's probably a really important part, a key part to getting this longevity benefit without actually having to eat less potentially.
John Speakman Maybe what you could do is you could take something that switches on MP Y and then you would switch on all these things that are related to lifespan, but you wouldn't actually be eating any less food.
Eddie This sounds like something out of a sci fi novel. You can eat whatever.
Juna But you're hungry.
Eddie You're always hungry. That's not something I would look forward to.
Juna I was just going to say I was like, I don't even want to live longer if I'm hungry. It doesn't matter if I'm eating, if I'm hungry all the time. Like, I don't like that, you know? I mean.
Eddie And you might end up eating a lot more.
Juna Yeah, I'm always hungry, right? I don't know. I don't know. All right.
Eddie But you may end up with a couple of more years of Life.
Juna Maybe so. In conclusion, I think we can pretty safely say that calorie restriction may or may not lead to life extension, but I can almost guarantee you it will lead to being pretty miserable all the time because you can't eat enough.
Eddie So. All right, I'll have to think about these extra couple of years before I start heavily restricting.
Juna Yeah, I don't think I don't think it's for me guys. We want to say thank you so much for listening to today's episode. We will link to Professor Speakman's papers on our website as well as all the other studies we talked about on foodweneedtotalk.com. You can follow us on Instagram at @foddweneedtotalk. You can find me on Instagram @theofficialjuna and on YouTube and Tik Tok @JunaGjata and you can find Eddie at the supermarket checking out what's going on with the royals today. Food We Need to Talk is a production of PRX.
Eddie Our producers are Morgan Flannery and Rebecca Seidel.
Juna Tommy Bazarian is our mix engineer production assistance from Isabel Kirby McGowan.
Eddie Jocelyn Gonzalez is executive producer for PRX Productions.
Juna Food We Need to Talk was co-created by Carrie Goldberg, George Hicks, Eddie Phillips and me.
Eddie For any personal health questions, please consult your personal health provider. If you enjoyed Food, We Need To Talk. Please share it with a friend.
Both: Thanks for listening.
