Modern longevity is crowded with promises, but the useful conversations stay close to biology. This discussion on nutrition timing and longevity points to a steadier truth: healthspan is shaped by the signals we repeat, the capacity we preserve, and the recovery (read the full breakdown) we protect.
Full transcript with timestamped links back to the original YouTube conversation.
Biology respects moderation. Just three cycles of a fasting mimicking diet reduced the biological age of those people on average by 2. 5 years. Light resets the brain's clock and food resets the body's clock. Your body processes food best earlier in the day. No complicated rules, no rigid meal plans. It can be really simple. What happens when [music] we don't ever give the body a break from food? Now, women often ask me, "Is fasting the same for us as it is for men?" Another common question I get is, "I've hit a plateau. Now, what should I [music] do?" So, here's how I troubleshoot. Welcome to Lifespan, a show where we discuss the cuttingedge science of aging and how to live healthier at any stage of life. I'm David Sinclair, a scientist and professor working on understanding why we age and discovering new ways to slow and even reverse the aging process. On this show, I share an insidider look at the latest [music] from my lab, the field, and what's just around the corner. [music] Hi everyone. This is a really great episode. I'm excited to share it with you. There was so much to tell you about fasting that I actually had to split it up into two parts. This was a fun episode to record and at times it got personal. I'd actually been fasting for 3 days before filming coincidentally and I was powering through it, but it really was a lot of information and you'll see you'll hear a lot of new things. But I had to ask Marissa to go get me some nuts uh so I could really keep going. I also show some of my own real-time biometric data such as blood glucose levels. And I also tackled the big questions for you about fasting like will you lose muscle if you fast and how to stop that? Will it tank your sex drive? and does your brain actually shut off without snacks? And as always here
off without snacks? And as always here at Lifespan, we really appreciate you all hitting that subscribe button and joining also us at lifespan. com where we're building the world's largest longevity community. You'll get notified about new episodes and it really helps us fund medical research into longevity and to make an even better show. Okay, let's go. Today's episode is part two of calorie restriction fasting. If part one was about why calorie restriction and fasting work, this part two is about how to make them work for you. In part one, we laid the scientific foundation for why eating less is one of the most powerful tools we have for extending your life. We talked about the difference between calorie restriction and fasting and why our ancient biology is poorly matched to a world of constant food. So, definitely check that out if you haven't yet. But of course, understanding the science is only half the story. A key question is how do you actually use this in real life? How is it even possible? That's what this episode is about. Today, we're going to get into much more practical advice. We're going to look at chrono nutrition, the timing of meals, and why your body might handle food very differently in the morning versus late at night. We're going to talk about timerestricted eating and prolonged fasting. what's happening inside your body hour by hour when you stop eating and why processes like autophagy, your actual recycling of proteins in the body, why this process is just so exciting when it comes to longevity. We're also going to get into things that people often ask me. Will fasting make you lose muscle? Does it affect your hormones and your libido? Does it raise your cortisol? Is it bad for sleep? and most importantly, how do you implement calorie restriction or fasting in a way that's safe, sustainable, and personalized? I'll also share some of my own fasting tips and tricks. It really isn't that hard, and the health payoffs are huge. Many of us aren't necessarily eating too much. We're just eating too
eating too much. We're just eating too often and often too late in the day as well. Something that I do way too often. So, here's the thing. Your body doesn't just care about what you eat. It cares about when you eat. That's the core of what's called chrono nutrition. It's the science of syncing meals with your body's internal clocks. One study led by my colleague Sachin Panda Andrew call up a picture of Sachin. He's looking very handsome on that that picture there. They studied so-called healthy average Americans. And by healthy, they looked at 156 people ranging from age 21 to 56, a huge BMI range, from 19, which is pretty thin, to 36, which is obese. And none of these were shift workers. So what did they find? They found that on average they ate every 3 hours, which is pretty much grazing all day long, and half of the participants were eating over a period of 14 hours or more per day. And they were eating late in the day, too. More than half of them ate a third of their daily calories after 6: 00 p. m., which, as we'll see later, is not great for your health. And in other studies, they found that only 13% of overweight or obese people fast for more than 12 hours a day. Most people start eating early and finish late, effectively turning eating into a roundthe-clock activity. You've probably heard of the master clock in your brain. The one that runs on light telling you when to wake up and sleep. But here's what's interesting. You also have clocks in your liver, your pancreas, your gut, and even your fat cells. They have their own clocks that are determined not by when we sleep, but predominantly by when you eat. That's one reason I try not to eat much on planes when I'm changing time zones. It throws my clocks off. These signals called zitgivers or timegivers set your internal rhythms. Light resets the
internal rhythms. Light resets the brain's clock and food resets the body's clock. So what happens when you eat a big meal at 10 p. m.? Your brain thinks it's time to rest, but your organs think it's time to digest. And it's that mismatch, what we call metabolic jet lag, that can mess with your sleep, impair your glucose control, and drive more fat storage. I suffer from this greatly. I've been known to go to the fridge late at night looking for something to snack on. It's very hard to close the door without taking something out. Around 15% of your genes, especially those tied to metabolism, follow a circadian rhythm. Your insulin sensitivity, for example, is highest in the morning, and that means your body processes food best earlier in the day. So, when eating patterns don't line up with your body's clock, the result is metabolic dysfunction. Some researchers even argue that obesity itself may be partly a chronobiological disease. It's not just about how much you eat, but just as much when you eat. Sachin coined the term timerestricted eating and showed that when animals eat in sync with their body clocks, they live longer and much healthier. So for humans, one simple rule follows. Avoid late night snacking. I truly believe that by fasting I don't just stay slim, but I'm going to live longer. And now you'd think that everyone would be on board, right? Well, that's actually not the case. There's still a lot of skepticism. Andrew is going to call up a study where they surveyed people. And it turns out that 66% of people say they're happy to exercise, and more than 80% said they'd take supplements. But when asked about intermittent fasting, only 30% were willing to give it a try. Maybe that's more after this podcast, but generally it's one of the least popular things to do to extend lifespan. So why the hesitation? Well, maybe it's because
hesitation? Well, maybe it's because fasting doesn't come in a pill or a powder, and there's no gym for fasting where you can hang out with friends. There's no colorful drink or an immediate endorphin rush when you're fasting, though it does come later. It also runs counter to billions of years of evolution where if you didn't eat the food that you had or eat, you know, pretty much when you could, it usually meant you didn't survive. So maybe you've thought about fasting and haven't tried it or you tried it and gave up because you were hungry. So what I want to do now is talk about practical approaches that might help you to try fasting and stick with it. One of the things I love about fasting is how simple it is. You don't need to overhaul your diet. It actually saves money. And whether you're keto, carnivore, plant-based like me, or something in between, fasting doesn't tell you what to eat, only when. And that's liberating. No complicated rules, no rigid meal plans. It can be really simple if you decide to say just eat between 10: 00 a. m. and 6 p. m. That naturally reduces caloric intake. You don't need a food diary. You don't need a tracking app. You just need to make the decision. The good news is it isn't just for people trying to live longer healthier. It can also fight diseases. So if you have type 2 diabetes or fatty liver, it'll really help you as well. We don't yet have absolute proof that fasting extends human lifespan. That's a very long clinical trial. But we do have strong evidence that it helps us live better and that's what really matters. Let's look at a 2024 study from Vulta Longo's group. They studied humans and they showed that just three cycles of a fasting mimicking diet, also known as FMD, increased the predicted median lifespan expectancy of those people. In other words, they were predicted to live longer and it reduced the biological age of those people on average by 2. 5 years. And the biggest benefit was in people aging the fastest. So fasting doesn't
aging the fastest. So fasting doesn't just reduce biological age. There are other health benefits. One is weight loss. Studies show that people can lose 3 to 5% of their body weight in just 1 to 3 months on timerestricted eating. Also, the cardiovascular system benefits. We see lower blood pressure, better blood lipid profiles, and slower age related changes in the heart and blood vessels. The brain benefits too. We see better memory, sharper executive function, reduced insulin resistance in the nerve cells, and even a slower pace of brain aging. Perhaps surprisingly, fasting also improves mood. Sure, in the first few days, it can be rough until your liver adapts and starts making glucose, but then the ketones kick in and they feed the brain and that sharpens mental clarity and stabilizes your emotions. And finally, what about sleep? Well, there's actually no downside there. And fasting's benefits extend beyond the brain. In mice that have glaucoma, which is pressure in the eye, every other day fasting suppresses the death of the retinal nerves. It slowed down the retinal degeneration and it improved the vision similar to what we see with our work with OSK epigenetic reprogramming. Most people who fast do it for at most a day, typically half a day. It's very rare that we go 3 days or longer. But let's talk about those prolonged fasts. That's when a remarkable process kicks in called autophagy. You've probably heard of autophagy. It's the recycling part of your cells. And it literally means self-eing. And it's one of the best things your body can do to stay healthy and functional. So here's how it works. And if you can't see the screen, you can go to the show notes. You can see that first the cell identifies what's damaged or no longer needed. mostly broken proteins, but also worn out organels. That includes mitochondria and other things that don't serve the cell anymore. The cell wraps
serve the cell anymore. The cell wraps them in a bubble-like membrane called a fagaphore. Think of it like putting trash and clutter into a giant trash bag. That garbage or trash bag then closes up and seals into something called an autofagome. It's a little capsule holding all the junk. Then it fuses with a lossome which is like this recycling center. Losomes in fact are full of powerful enzymes that can break down pretty much anything biological. Once the fusion happens to the loome, you get an auto lossly and the real cleanup begins. Then everything inside gets broken down into its building blocks. Proteins become amino acids, fats become fatty acids, and carbohydrates become sugars. And here's the amazing thing. The cell doesn't just throw that material away. It recycles it using the parts to build fresh, healthy components. Let's talk about what happens during an extended fast. Here, your cells start switching on a more specialized type of autophagy called chaperone mediated autophagy or CMA. I know CMA pretty well because it was discovered by my good friend Anna Maria Quervo at Albert Einstein College of Medicine in New York. She's a great person who constantly drinks colas cuz she's working about 18 hours a day. She showed that if you stop age related decline of a protein that she discovered called LAMP 2A in a mouse of course you can actually keep CMA running smoothly even in old age. And those mice, they had much healthier cells, better immune function, and slower rates of aging. Turning on other autophagy genes like ATG5 or Becklin one, which are part of another cellular cleanup process, that actually extends the median mouse lifespan by up to 17%. So, what else happens when you go on these extended fasts for over a day? Well, you start to see improved DNA repair and less oxidative stress in your tissues. You'll
oxidative stress in your tissues. You'll even experience rejuvenated mitochondria and they give more energy. You'll have more stem cells and neurogenesis, which is the turning of stem cells into nerve cells. You'll have more clarity and thought, and this is probably because you've got more ketones, which is the major fuel for the brain. If you're a regular listener to this show, you'll know that I've long been interested in how fasting may affect brain health. And you've likely heard of ketones in the context of the ketogenic diet or in fasting. By cutting back on carbohydrates, what you're actually doing is flipping a switch that tells your body to start producing these molecules as an alternative energy source besides glucose. In the lab, animal studies, particularly in rodents, but also now in humans, eating less often or reducing your calories, has been linked to improvements in metabolic health, insulin sensitivity, and even biomarkers of aging. Ketone IQ is a drink whose active ingredient is a ketone precursor called R13 butin dial. What's really interesting is that your liver converts that molecule into a really important metabolic fuel called beta hydroxybutyrate or BHB which your brain and your muscles can use for fuel. There's a growing amount of research into the effects of ketones. For example, in 2012, the first study of its kind showed that consuming drinking exogenous ketones could raise blood beta hydroxybutyrate levels to that typically seen during a long fast like the ones I like to do. Then in 2018, another study asked an interesting question. What fuel does the aging brain still use? As cognition declined, what the researchers found was that the brain became less able to use its normal fuel, glucose. And what actually happened was that the ketone uptake remained relatively preserved. So that's really interesting because what it suggests is that even when the aging brain struggles to use sugar for energy, it can probably still use ketones as the fuel. So if you would like to try Ketone IQ, we're offering
like to try Ketone IQ, we're offering you a 30% off discount for your first monthly order at ketone. com / lifespan or at the checkout. Just use the code lifespan. Extended fasting also improves metabolic flexibility, the ability to switch between burning carbs and fat, something that many of us have lost. Fasting is even associated with lower cancer risk by breaking down damaged cells and shifting metabolism into a more oxygen efficient state. It creates an environment where cancer cells struggle to grow. It's called a respiratorylike state. But healthy cells stay protected, which is the best part about it. And fasting doesn't just work through autophagy, the protein recycling mechanisms we talked about. It activates longevity pathways, the certuins, AMPK. It lowers IGF-1 and mTor activity. It also reduces inflammation, clears scinsesscent cells, and it improves nutrient sensing, which is very important for longevity. It even counteracts the premature aging that comes with obesity. There's also evidence that fasting can raise NAD levels and spermadine, both of which can stabilize the epiggenome. We'll talk about spermadine in a future episode. Caloric restriction is difficult. Even fasting, I find for 24 hours is really challenging. I rarely fast for more than 24 hours. Today, however, I've been fasting. We just realized for 3 days now, partly because we've been so busy filming the podcast. I've got a couple of glucose monitors on my arm, and it's really quite amazing how after a few days, your glucose levels really flatten out. I'm certainly not hungry, and if I am, you know, I have a little bit of tea here. Tea is fine. I thought I'd share with you what's going on on my glucose monitor. I'll call it up on the screen and we can have a look at what's going on in my body. So, here we see uh on the monitor. This is since 2: 00 this afternoon. It's
This is since 2: 00 this afternoon. It's now the evening and you can see how flat my glucose levels are. They're not spiking at all. My liver is making its own sugar. I don't feel hungry at all. It's quite a good feeling. I feel really awake, alert. My brain's working well. I've got lots of ketones circulating through my blood which are feeding my brain. Probably my breath is a little bad because ketones tend to come out through your mouth as well. But that's how it is. You know, you drink if you're a bit hungry. Drink lots of liquids. Of course, if you're burning fat, you need liquid. You need water to break down fat. So, remember that. But I think this is a good example of how things are when you're fasting for a while. You get into the groove. You don't feel hungry. Usually after about the second day, I do feel hunger and I think I got to go to the fridge and eat something. But if you can bust through that, maybe just get to bed, go to sleep, and forget about it. I woke up this morning, not hungry at all. I haven't really thought about food all day. I've been very busy, and it's been great. I'm thinking maybe I'll just go for another day. We'll see. What I really like about this actually is that I know that it's turning on my longevity genes. My NAD levels would be high. My certuin activity would be high. My mTor would be repressed because remember there's not a lot of amino acids now in my system. And you know, I think you just feel great. Of course, I don't always fast for three days. I rarely do. Maybe only a few times a year. But fasting during the day, I find it to be very healthy and very helpful. First of all, it means I can eat a much bigger dinner. So, my typical day is like this. I skip breakfast when I can, unless I'm socializing. I'm not hungry till mid to late afternoon. If I get a little peckish, I just drink more. I have tea. I have a matcha, green tea, which is very healthy, or a black tea. And then towards the middle of the day, towards the later afternoon, I might eat a few nuts if I really feel like I need some energy. But but I definitely almost every night, I eat a decent dinner. I tend to focus on plants, of course, but if I eat out, I eat a regular restaurant meal and I feel fine. And the best thing
meal and I feel fine. And the best thing about actually doing this diet is I can eat a really large meal at dinner and not feel guilty and not put on weight. And having switched to a a window of eating which stretches from about 3: 00 in the afternoon to about 9: 00 at night, I've been able to keep my weight at a very consistent level. Of course, I'm monitoring my weight every morning and I actually have a graph of my weight every morning and I can see if I've gained a little bit and I adjust. And it's been scientifically shown that maintaining a consistent body weight is very important for long-term health as well. So I'm not fluctuating my weight too much as well. Of course in holidays sometimes I gain a few pounds, but I very quickly within a matter of a week or two get my weight back down to what I regard as my optimum. So what works for me is this 6-h hour eating window from 3: 00 p. m. to 9: 00 p. m. most days of the week. And that means I get an 18-hour fast. We call this the 186 fasting window. Some people want to eat for longer. They might choose to eat for seven or eight hours. That's also fine. There are others who prefer to eat in the morning. I wake up and I'm not hungry. I have no interest in food. But others do. Or maybe you work out in the morning and you feel like you need that extra energy. That also works. But if you eat in the morning, I would consider eating a smaller lunch and skipping dinner. Again, you're getting that 16 or 18 hour window of fasting which turns on the sertuins, turns on amkinise, downregulates mTor, and you get the benefits of longevity, just eating at a different window during the day. And so, I'm very happy with my numbers now at this 3-day long fast. If I was to eat something now, you'd see it spike up probably to over 100. And that's pretty typical for when you eat a meal. But what you want to see is that your glucose levels come down very quickly after about maybe half an hour or an hour. That shows that you're insulin sensitive. Your muscle, your brain takes up that glucose very quickly. In
up that glucose very quickly. In contrast, older people, especially those that are insulin resistant, type 2 diabetics, take a much longer time for that glucose level to come down. What I'm showing you is a continuous glucose monitor. You can see I'm now down to 69, which is a great number. This is continuously monitoring my glucose levels. It's a little patch that you stick on your arm and it's sampling the liquids that are just underneath my skin. It doesn't hurt to put on. And what's really great about it and what I love about having this is first of all, it reminds me to be good about my diet. When I'm not wearing it, I'm much less likely to be aware of what I'm eating or care about it. But since I've had this on, I've actually paid a lot more attention to what's going in my mouth. That's the first thing. And the second thing you learn is how do you respond to certain types of food? And that's very important because we all respond differently. For me, I respond in a negative way to white rice and grapes. I was surprised about grapes. I thought they'd be fine as a snack, but actually my blood sugar shoots up rapidly every time I eat just a couple of grapes. You'll learn very rapidly what kind of foods are good for you and which ones to avoid. I really encourage you to learn how your body responds to food because it's one thing to just put it in your mouth and hope for the best, but when you see the readouts on your phone, it's really great positive and negative feedback and you very quickly learn which foods to eat and which foods to avoid and even why you're getting hungry. What you'll notice is if you have a crash after eating a meal or eating grapes, you'll feel really hungry and you'll learn how to stabilize your glucose levels so you don't get those pangs of hunger during the day. A question I get a lot is how long do you need to fast to trigger the beneficial effects? To answer that, let's first walk through the timeline of what happens inside the body the longer you fast. After a meal from 0 to 4 hours, you're of course in the fed state. Blood glucose rises, insulin also rises, and you're running mostly on that meal. Excess sugar gets
mostly on that meal. Excess sugar gets stored as glycogen in the liver and the muscles. Hormones like GLP1, PY Y, and leptin increase as well, telling you that you're full, while ghrelin, the hunger hormone, drops dramatically. Between 4 and 12 hours after a meal, digestion then is mostly done. Blood sugar and insulin begin to fall and the body starts using liver glycogen. Grein increases as the stomach empties, which sends hunger signals to the brain. And in the hypothalamus, one of the lower deep parts of the brain, appetite stimulating neuropeptides like neuropeptide Y and audi related protein rise. And something else that happens 3 to 6 hours after eating is that fat breakdown or lipolysis begins. By 12 hours, glycogen is starting to get depleted and a hormone called glucagon starts to rise and glucagon triggers gluconneogenesis, which basically stands for making new glucose. And it does that from amino acids and glycerol. That's the green line on the graph here for those of you who are watching. Between 12 and 18 hours after your meal, fat burning ramps up even more. Now you're running mostly on free fatty acids or FFAs. Ketosis begins around 16 hours and for most people it doesn't fully kick in till about 24 hours. That's also when autophagy starts to really switch on. That's the protein recycling. Ketosis is when your body produces ketone bodies for fuel. These are molecules like acetone. They tend to give you a bit of bad breath, but your brain really loves to consume them. They called ketone bodies because biochemists many decades ago isolated them as separate substances or bodies from urine in diabetic patients. Then from 18 to 24 hours with all those ketones in your system, something fascinating happens. Your alertness actually rises and I actually
alertness actually rises and I actually feel this when I take a shot of the ketones. Besides ketones, certain hormones rise like adrenaline and noradrenaline. Evolutionary, this was probably the time you needed to be sharp and motivated to go find food. At this stage of fasting, from 18 to 24 hours, thanks to more fat breakdown and some more gluconneogenesis, your brain and body get steady energy. By 24 to 36 hours, your liver is now producing even more ketones. These aren't just fuel. They're actually signaling molecules that turn on antioxidant defenses, improve mitochondrial efficiency, and even protect neurons. This is why many people report the fasting high which is sort of a calm clarity that they get. Also at this stage catakolamines like adrenaline rise even further mobilizing your fat stores. Growth hormone surges as well preserving lean muscle repairing tissues and supporting fat burning. Many people even notice their skin looks healthier after a prolonged fast. By 36 to 48 hours, you're in even deeper ketosis. Autophagy is probably at its peak. The body is now running almost entirely on ketones and fat. After 48 hours, ketones now dominate over glucose in the blood, and the brain relies on them for its fuel, sparing muscle from being broken down. If you go 3 days, what turns on is what's called chaperone mediated autophagy, the really deep cleansing of misfolded and damaged proteins. That's about the limit that I've ever done. Some people go even further. They can go for a whole week without eating. I've never done that, but I'm sure that that has other benefits as well, including the real deep cleanse and of course weight loss if that's what you're looking for. But now, let's talk about the opposite. What happens when we don't ever give the body a break from food? And that's how most people these days live. With frequent meals, blood glucose stays high and the pancreas is constantly pumping out more and more insulin. Over years, cells stop responding to that hormone and we get insulin resistance.
resistance. The pancreas shouts louder, pumping out even more insulin, leading to chronic hyperinsulinemia, which just means too much insulin all the time in the blood. Left unchecked, this drives type 2 diabetes, weight gain, and for men, erectile dysfunction. This constant high insulin increases inflammation. It reduces fat burning and suppresses autophagy. So instead of steady energy, you get crashes, brain fog, and cravings. This is the standard lifestyle of today with those constant meals and snacks in between. That excess sugar and fat, they don't just collect around the waist. They get stored in the liver, your pancreas, muscles, and even the heart. That's ectopic fat, and that's the most dangerous type of fat. Constant grazing, three meals a day plus snacking. It also disrupts circadian rhythms. Your sleep suffers and hormones become imbalanced and that in turn makes insulin resistance even worse over time. The cycle just accelerates aging and makes you in later life susceptible to diseases not just diabetes but even heart disease and Alzheimer's. And that's why fasting done correctly is really important. It breaks the cycle. It restores autophagy. It improves insulin sensitivity and it reactivates the body's built-in longevity systems. Okay, let's take a moment to bust some myths because like most things in health, fasting is nuanced and it's easy for the science to get buried under the internet hype and misinterpretations. Okay, myth number one, fasting will make you lose muscle. I hear this all the time. It's a common fear and it sounds quite reasonable, but if you fast wisely, not only can you preserve muscle, you can actually improve your body composition. In fact, a 2025 meta analysis of 15 studies showed that healthy adults who practiced timerestricted eating and they exercised regularly lost more fat than those who exercised alone. And importantly, they
exercised alone. And importantly, they also preserved their fat-free muscle mass. The key here is to make sure you're getting enough high quality protein, whether that comes from animal or plant sources. The current recommendation is 1. 2 to 2 g of protein per kilogram of your body weight every day. of course depending on your age and activity levels. This is 0. 5 to 0. 9 g per pound of body weight for those in the US. But more is not always better. Too little protein can contribute to muscle loss and frailty. While too much protein, especially if you're eating very high amounts, like 2 to three grams per kilogram of body weight, can also have downsides like especially in the long run like high risk of type 2 diabetes and especially if that protein is from red or processed meat. branch chain amino acids leucine, isolucine and veene which are found more in meat than plants. They actually activate mTor which we've talked a bit about before which is good in the short term for the body. It helps you heal grow but in the long term the goal is actually to keep the activity of mtor low. So actually I prefer to eat plant protein much more than meat. So let's talk a bit about this. It's a common argument on social media. There are the protein folks and the meat folks and the plant folks. They're often debating which is best. What do I do based on the science? Well, personally, I tend to work out first of all to maintain my muscle mass as best I can, though it is hard when I travel. I tend to focus on plants much more than animals. In fact, I try to be as vegan as I possibly can. And I try to stay closer to the lower end of the recommended ra range of daily protein intake. And just to be clear, it's a personal choice. It's not necessarily a recommendation. And I'm not trying to be Mr. Universe, of course. And my my profession definitely doesn't depend on having a lot of muscle, but I do things that really count. I take the stairs when I can. I have weights uh in my TV room. Uh and I also have a standing desk every day with my doctor. I monitor my
every day with my doctor. I monitor my amino intake and nutrients and my blood levels. Every few months I go and have that tested to ensure I'm not deficient in any of these. And one reason I do this is because of great work by my ex - studentent Dudley Laming who's now an associate professor. His studies in mice have shown that reducing certain amino acids, the branch chain ones, especially isolucine, can greatly improve metabolic health and even extend the lifespan of those animals even when total calorie intake is the same. And I know I'm not a mouse, but the fundamental biology is the same between those animals and us. So now that doesn't mean we should all just slash our protein intake in the hopes of living longer. Humans are not mice. And as we age, muscle is very important for other things like stability, independence, avoiding falls, fractures, and even maintaining hormone levels. But for now, the practical point is simple. If you're fasting, make sure that when you do eat, you get enough highquality protein to preserve muscle and of course all of the nutrients that you need. And remember, to prevent muscle loss in general, you do need to move and lift things. There's no way around it. Strength training is the signal to your body to keep building muscle. We know from being in space or just sitting in a chair, your muscles are just going to degrade. You need to counteract that. So get up off your chair and walk, move, and if you can, lift weights. Let's remember that muscle is a longevity tissue. Building skeletal muscle helps reduce fat mass. It improves glucose control, and it supports insulin sensitivity. Another reason you want to preserve your muscle mass is because muscles secrete what are called myioines. These are little molecules, sometimes just little peptides, that move around your body and help keep other organs healthy. One of the things that we've talked about in this episode is that longevity really comes down to daily habits. Things like when you eat, how often you eat, and how much you move. And the good
eat, and how much you move. And the good news is that even small changes when you stick with them over time can have a big impact on your health and your lifespan. Which brings me to a wearable that I'm particularly fond of. Partly because of its scientific foundation at Harvard, where I work, but also the founder's own research and scientific rigor. I'm talking about the Whoop band, which is the one that I rarely take off my wrist. This wearable is a health and fitness coach that gives me insights into my sleep, recovery, and my body's strain. Researchers have studied how accurate the device is. And in a 2022 study, they compared six wearable devices, including Whoop, against clinical grade ECGs and sleep recording devices. Whoop showed strong accuracy for heart rate and heart rate variability. Two measurements that are really important. Wearing the Whoop over the last two months, I've seen dramatic improvements in my personal biomarkers. For example, my resting heart rate has gone down to 45, which is a quite a low number for me. And my heart rate variability, which you want to be high, has shot up to 90, putting me in the top few percent for my age. If you want to get a free Whoop 5. 0 mono smart band and a month off membership. Go to join. woop. com / lifespan or at checkout use the code lifespan. All right, let's talk about myth number two that fasting destroys your sex drive and your reproductive hormones. Let's start with a mouse study that's fairly recent and in fact I I posted about this on X back in May 2025. In a recent cell metabolism study, old mice on intermittent fasting had better libido. They they were very horny in this study and they had more frequent reproduction and this is probably because the fasting reduced brain tryptophan which lowered their serotonin and released the break on the libido. And in men and women what we see during intermittent fasting is that levels of testosterone, estrogen, SHBG which is sex hormone binding globbulin and other sex hormones they
globbulin and other sex hormones they usually remain stable even after a year of intermittent fasting. And in women with PCOS, which is polycystic ovary syndrome, fasting can even improve hormone balance. So no, besides maybe giving you bad breath from all the ketones and reducing your alcohol consumption, fasting isn't going to ruin your sex life. So now myth number three, will I be hungry all the time? It's true hunger and cravings are common in the first week or so of fasting. With ghrelin rising, which is your main hunger hormone, but it usually adapts by week two or three, the hunger spikes calm down and fasting becomes easier. I usually find in my second week, I don't even think about food. All right, now we're up to myth number four. My brain will shut off without food. That's actually completely false. After the second week of fasting, you get really used to it. If you run out of glucose, your body makes ketones. And this is actually really good for your brain. In fact, many people find that they think more clearly when they're fasting. All right, the next one. Myth number five. Fasting spikes cortisol, and that's dangerous. This is kind of true. Cortisol can rise during fasting, but it's actually temporary. It's an adaptive rise, much like exercise. It's really hormesis. What doesn't kill you makes you stronger. It's a mild stress that makes the body stronger. That's not the same as the chronic harmful type of cortisol rise that you see in people who are stressed or just work out too much. So, no, the rise in cortisol is probably not a problem during intermittent fasting. Next one, myth number six, fasting ruins diet quality. That's also not true. Studies show that whether people eat in a 4-hour window or a 10-hour window, their overall diet quality stays about the same even after a year. Macronutrient balance, proteins, carbs, fats, they stay stable. The sugar, saturated fat, cholesterol,
sugar, saturated fat, cholesterol, fiber, and sodium all stay steady. All right. Now, let's talk about myth number seven. This is a common question I get. Will fasting lead to eating disorders? This one sounds alarming, but the data don't support it. In healthy adults, intermittent fasting has actually been linked to less anxiety around body image and fewer food cravings and even reduced binge eating compared to people who don't fast. In fact, many report feeling more in control of their food, not less. So rather than fueling disordered eating, fasting when practiced mindfully actually might help build a healthier relationship with food. All right, so we've covered the myths, but like any good story, there's a twist. So let's talk about things that aren't known or agreed upon. Let's start with intermittent fasting versus calorie restriction. Which is better? In animals? Intermittent fasting extends lifespan in part by turning on cell defenses similar to calorie restriction. Unlike animals in humans, we just don't have strong evidence that fasting is equal or superior to calorie restriction for most people. But that said, fasting does have some unique benefits for brain health, cancer therapy, and even sleep that calorie restriction doesn't seem to provide. Moving on to the next concern. There's a 2024 conference abstract that many people saw. It made headlines at the time. It followed about 20, 000 people for 15 years. It reported that people eating within an 8 hour window, a short time window, actually had higher cardiovascular mortality, compared to those eating over 12 or 16 hours. Timerestricted eating also didn't show any benefit for overall lifespan or mortality risk. Sounds like a death blow for intermittent fasting, right? But here's the problem. The study was observational. It relied on self-reported data, and it also didn't
self-reported data, and it also didn't account for diet quality and could reflect reverse causation. And it didn't account for confounding factors like pre-existing illnesses or lifestyle differences. We know that people when they answer questions, they always lie or they at least don't remember correctly. So, while the study raised questions, it certainly doesn't outweigh the decades of controlled studies showing that fasting does improve metabolic health and reduces disease risk in humans. So, now that we've covered the science, let's get practical. I know many of you have been waiting for this part. I'm going to give you a step-by - step guide on how to safely implement CR or fasting. But before we get into the nuts and bolts of all of it, I need to be clear. First of all, I'm not a medical doctor. or I'm a PhD scientist and this podcast is for educational purposes only. Nothing here should be taken as medical advice, a diagnosis of any condition or a treatment. And always consult your doctor, your physician before making any changes to your diet or your lifestyle or your medications. Well, with that disclaimer out of the way, let's talk about the ins and the outs of fasting and how you might try it. So, are you a good candidate? Let's talk about that. So fasting and the more severe calorie restriction are very powerful tools, but of course they're not for everybody. You're probably fine if you're generally healthy, aged between 25 and 70, have a stable weight, and can sleep well, get some exercise in, and manage stress pretty well. Bonus points if you've got social support. But there are red flags, what doctors call contraindications. It's a no-go unless your doctor says it's fine. If you're pregnant, you're breastfeeding, trying to conceive, under 18, underweight, or have a history of eating disorders, just really be careful and always consult your doctor when doing something major like this. The second thing to consider, step two, is what type of calorie restriction or fasting is better for you and your lifestyle. Calorie restriction is more
lifestyle. Calorie restriction is more severe. You're eating less, you're also eating more often. Whereas fasting is skipping meals or even skipping whole days of eating. There's also fasting mimicking diets that you might want to consider. Choose what supports your lifestyle and your other good habits like sleep, exercise, and relationships. If you prefer flexibility, timerestricted eating could be easier for you. Or maybe the five two method, which is 5 days of eating normally and 2 days of eating low amounts of calories, perhaps one meal a day or even skipping all the meals. If you're interested in calorie restriction, the sweet spot might be about 10% fewer calories than normal or maybe even 25% if you want to go even more extreme. But definitely not starvation. I want to be clear. You do not want to enter a period where you've got not enough nutrition. That's not what this is about. It's all about adequate nutrition. Just enough reduction to trigger the health benefits while still fueling your body with enough protein, fiber, nutrients, and hydration. All right, the next step, step three, get a health check. You need to know what the baseline level is. First of all, to know if you're healthy enough, but also to know if what you're doing is actually working. I'll talk more about the specifics next, but you want to get a baseline set of labs, your vitals, even your physical performance, and of course, record things like sleep and stress. If everything looks good, you want to go for it. So, how do you do that? Let's talk about step four. You want to ease into it. Don't go monk mode on day one. You'll fail. You want to cut back slowly. Start with about 5% fewer calories than normal. Then start to shorten your eating window gradually. Drink plenty of water, tea, coffee. These help with satiety. You want to note down your energy levels, how hungry you are, and if your sleep and your mood is affected. All right, let's talk about the things that actually make fasting or calorie restriction possible. Rule number one, food and drink quality matter. This is
food and drink quality matter. This is why some studies of fasting and plant-based diets don't show huge effects because not everyone eats quality food. You can be vegan and still eat potato chips every night or French fries. That's not healthy vegan. That won't work. You want to go for high satiety foods. These are foods that reduce your hunger and satisfy you. Also, go for nutrientdense foods and whole unprocessed foods. These are things that you'll want because you're not eating as much typically, certainly not as often. Things that your grandmother would recognize. Eat foods that keep you full like nuts. Almonds or walnuts are great. Soups, oatmeal, yogurts. I choose vegan yogurts. Boiled potatoes are great. Pulses and legumes like chickpeas, beans, and hummus. I love baba ginosh, too. Choose foods with volume and nutrients without piling on the calories. Think leafy greens. Those are great cuz they fill you up, but they also have a lot of vitamins as well. Make sure you maintain enough protein intake. That's important for maintaining muscle mass. You'll be exercising. You also want to support your metabolism, and they also help reduce cravings. Protein is the best way to prevent hunger. Use herbs and spices instead of heavy sauces. Turns out spicy food actually can help with metabolism and reduce consumption of food. If you're doing calorie restriction or CR, think like a strategist. Learn how to read food labels. There are apps like food ukate, open food facts, and others. The other thing you need to do is eat slowly. It takes 20 minutes for your brain to register fullness. What I like to do is I put my knife and fork down. I talk to people. I chew slowly. Makes a big difference to how much you eat. And often you don't end up finishing the meal. You feel full by the time you get through it. And whatever you do, don't eat while distracted. There's nothing worse than eating while watching TV or doing your emails or doom scrolling. These are appetite amplifiers. Personally, I try to leave about 30% of meals on the plate and put it in the
meals on the plate and put it in the fridge for later or take it home from a restaurant. I've also spent many a night watching TV while eating and I go to bed feeling full and that is the last thing you want to do. And if you're fasting, stay hydrated. I've mentioned this a few times, but it's so important. Make sure you drink a glass or two of water before meals. It helps you feel fuller and it slows down how quickly you eat. So, now let's talk about what to avoid. You don't need to be militant, but watch the usual suspects. Alcohol, I've given up. Especially cocktails and mocktails full of sugar. Avoid any sugary drinks if you can. Generally, all processed drinks and foods are bad. Other things to avoid, of course, deep fried foods, calorie bombs hidden in sauces, dressings, mayonnaise, and dips. Even though they taste great, you really want to avoid those and especially those if you look on the label and they contain a lot of high fructose corn syrup. Sometimes even a little bit of dressing can add more calories than the salad itself. So, be careful. And finally, you need to surround yourself with social support. You'll have slip ups. Take breaks when needed. Manage stress. And if your partner isn't supportive, in fact, sometimes it's worse, they encourage you to eat, talk to them. Explain why this matters and why this support is so important to you. And lastly, be realistic. Nobody eats perfectly all the time. You'll have slip ups. They happen. That's normal. I call myself a struggling vegan cuz I also sometimes have French fries. Sometimes I overeat, but that's okay. You want to break your fast gently. You want to monitor your health, especially if you're doing prolonged fasts. And don't fast if you get sick. You need to recover. So eat well during those times. So let's talk about how you actually know if your fasting or calorie restriction is actually working. Is it doing you any good? So that's where tracking comes in. So if you want to do this right and safely, get your baseline labs before you begin. Emphasis on before you begin.
you begin. Emphasis on before you begin. Then we'll retest every few months, especially if you're making big changes. Even before you get your labs, you can start simply. I would start by weighing yourself first thing in the morning. And you know, don't worry if you fluctuate daily. You really want to just track your weekly average. It's much more reliable than daily fluctuations. I step on an electronic scale that records my weight actually and even tells me my body fat. It's a wthing scale and I love it and I use it all the time. One of the big themes in this episode is that calorie restriction and fasting can improve metabolic health and support healthier weight loss over time. But one thing I always say is you cannot optimize what you don't measure. Many people only measure their total body weight if anything. But this only tells a small part of the story. When losing weight, you don't know if you're losing fat or muscle or even where the fat is being lost from. For instance, let's talk about visceral fat, the evil fat that sits around your organs. It's associated with increased risk of cardiovascular disease, diabetes, and even death. So getting rid of visceral fat in particular or at least minimizing it can have a strong impact on your long-term health and longevity. How do you measure visceral fat? Well, it turns out that Wings, one of Lifespan's partners, make some of the coolest devices that you can measure yourself with. Watches, a blood pressure monitor, and advanced bathroom scales. I've actually been using Wings devices for over 13 years since they first came out with their Wi-Fi scales. The Wings body scan scale can help estimate muscle mass, fat mass, and even visceral fat. So, let me show you what my body looks like in 3D. My digital twin on the Wings app. Here it is on the screen here shows changes in lean mass, visceral fat, and even bone mass. What you can see on my arms is 11. 3% fat and 14% on my torso. And visceral fat is pretty low at 2. 7. I'm happy with these numbers. You can
I'm happy with these numbers. You can also look at muscle. The wthing scale is also the only smart scale that comes with a an FDA cleared ECG, which is really important for monitoring your heart health. And I measure that every morning when I stand on it. So, we at Lifespan, we're partnering with Wings in part because we really believe in their product, but also because we share a common commitment to preventative health and also supporting medical research and young students. Learn more about Wings or get a scale or one of their other really cool smart devices at wings. com / lifespan. Or for a 10% off discount, use the code lifespan. The other thing you can do is measure your waist circumference and your waist to hip ratio if you're brave. Sometimes I just use my belt to tell, but it's much more accurate if you get a measuring tape. Turns out the waist to hip ratio is an excellent predictor of your metabolic risk. It's even better than your body mass index or BMI. Some people like to get what's called a DEXA scan, which stands for dual energy X-ray absorptometry. These are mild X-rays that look inside your body. Personally, I don't really like them. X-ray exposure should be minimal because they break your DNA, and my lab has shown that actually accelerates aging. So, what about blood tests? Let's go through them. Now, you can get these tests from your own doctor or online these days. By the way, these are all in the show notes, so you don't need to take notes. One of the most important things to measure in any blood test and especially when you're fasting or calorie restricted is fasting glucose. This is how much blood sugar you have after an overnight fast. You'll also want to measure what's called HBA1C, which many of you will know is when glucose gets attached to your hemoglobin. That's a more long-term measure of your blood glucose levels. You want to just make sure that you're not too low on those things and of course not too high either. Another thing you want to measure is your hemoglobin also your red blood cells and your hematocrit. The reason is that it often was low in the calorie study. So definitely monitor that and if it gets
definitely monitor that and if it gets too low discuss this with your doctor. Now the third thing that you want to measure, third group of things is your lipid profile. Generally you'll see improvements in these with fasting and calorie restrictions. So you want to know where you're starting from. So that'll include so-called good cholesterol, HDL, bad cholesterol, LDL, Apo B, LP, little A, and triglycerides, and probably more. Just talk to your doctor about that. When you're fasting and you're on calorie restriction, you need to make sure that you're not deficient in vitamins and minerals. So the vitamins that are important would include the B vitamins and vitamin D among others, and also minerals, especially iron, and also magnesium, zinc, calcium, and phosphorus. You also might want to measure your omega-3 index. Make sure you're getting enough omega-3s. If you're not eating fish or taking a supplement, you might be deficient. You want to measure your liver and kidney function. I typically measure inflammation markers as well, just to see them come down with my fasting regime. These include CRP, IL6, TNF alpha. Those are also good predictors of longevity. And also, it's really important to measure your hormones, especially if you're a female. That includes IGF-1, which is a longevity hormone. You want to have low levels of that. T3, T4, these are the thyroid hormones and for men especially, testosterone levels. Also consider taking a DNA methylation age test. You can get these online and they actually measure the chemical changes on your DNA and they estimate your biological age. And that way you can see if you're actually getting younger by doing this. Just a word about biological age tests. I like them so much and they're also based partly on our research. The reason I like them is that they're really encouraging. If I see a consistent dip over a matter of years, I really know that what I'm doing is working. I recently chaired a session at a conference at Harvard on the biomarkers of aging. And while the clocks aren't perfect, they're certainly getting better all the time. You also may want to use or try a continuous glucose monitor or a CGM. You also may want to track ketones. These go up, of course, as you're fasting. And the more
course, as you're fasting. And the more you get into ketosis, as it's called, the more you'll see those rise. and that's actually a good indicator if you're doing well. Tracking your vital signs is also really valuable. Your resting heart rate is good, heart rate variability, respiratory rate, and your sleep. If you don't already use a wearable, like a wrist strap, a watch, or a ring, I highly recommend one. Okay, let's move into some common questions I get all the time about fasting. Is there anything I can eat during my fast? I get this question all the time, but here's how I think about it. If you want to be strict about it, you really shouldn't be eating. I try not to eat and drink a lot, but a tiny bit of food is fine. So, personally, I have a teaspoon of yogurt in the morning with my supplements, and I might eat some nuts during the day if I feel peckish. I don't regard this as a fasting break, and it sure doesn't increase my glucose levels, and it doesn't lower my ketone levels. So, you know, I'm hitting my goals, so I'm not really worried about that. So, water, some black coffee, unsweetened tea, herbal infusions. These are all fine. Just don't overdo it. Especially on an empty stomach or you risk reflux or even gut irritation. And for those longer fasts over a day, make sure you're keeping up your electrolytes. You can get the salts that you add to your water or drink coconut water. Another question I get pretty often is, "What medications and supplements can I take on a fast? And how do I take them if I'm not even eating?" Always take your medications as prescribed. And if they need to be taken with food, you can still do that within a fasting framework. And while most supplements are fine while fasting, skip those protein shakes and especially those branch chain amino acid supplements. And as I said earlier, I often take my supplements, especially the fat soluble ones, with a spoonful of yogurt in the morning. So another question I get is how often should I eat? Well, actually the science says there's a whole variety of things that can work. It depends on you. For most people, especially beginners, eating two solid meals works best. I prefer to eat one meal a day if I can. That works well
one meal a day if I can. That works well for me. But in the beginning, it's a little tough. Over the first few weeks, you'll feel a bit hungry, and that's why two meals is a good start. When you start fasting, you'll find that it helps with your circadian biology, so you might even sleep better. It'll stabilize your energy, and it'll even improve your metabolic health. Focus though on quality food consumed twice or once a day and then naturally people ask should I skip breakfast? Is it important to eat in the morning? Well, it depends. Some scientific studies show that early eating aligns with better metabolism. Your body handles food better early in the day. And many people, especially women, around their menstrual cycle, they feel better eating before a morning workout. But if you're not hungry in the morning like me, don't force it. Most people's hunger hormone, ghrein, is at its lowest around 8: 00 a. m. anyway. I often skip breakfast, and it helps me fast longer. Just don't let skipping breakfast turn into binging late at night. I often do that, and I regret it the next day. Make sure you still hit your protein and fiber targets, too. Another question I get really often is, can I just work off the calories? Is that enough? Will I still get the benefit? Well, exercise is similar in how it affects the body compared to calorie restriction. First of all, both of them signal scarcity. They put the body in adversity mode, forcing the body to become more efficient and more youthful at the cellular level. But there are big differences. Exercise is not the same as fasting or calorie restriction. First of all, in multiple species, from yeast to worms, from flies to mice, and even monkeys, calorie restriction extends lifespan up to 50%. But exercise alone only improves health span and delays disease. It doesn't significantly extend maximum lifespan in most models. Second, calorie restriction maintains longevity mode continuously, whereas exercise only triggers it intermittently. Thirdly,
triggers it intermittently. Thirdly, exercise primarily acts on certain tissues and organs like muscle, liver, and the cardiovascular system. These organs are directly engaged in movement and energy metabolism. In contrast, calorie restriction affects every tissue by persistently lowering anabolic signals and circulating growth factors. Fourthly, calorie restriction uniquely activates aspects of DNA repair, epigenetics, and stem cell function. Exercise induces some of these changes, but not to the same magnitude or duration, especially in non-muscle tissues. So, the answer is no. You cannot outrun a bad diet. All right. Next question. Will calorie restriction or fasting hurt my exercise performance or gains? I hear this all the time. So, let's start with the science. In the calorie study, people who restricted calories for 2 years without any structured exercise, they didn't lose any aerobic capacity. In fact, their V2 max adjusted for body weight improved. Their muscle quality went up too, even though absolute strength and lean muscle dropped a little. And a 2019 study of women who had been resistance training showed very similar results. An 8-hour eating window still supported muscle growth and performance. And a 12week long study of untrained people found that resistance training, oh, Andrew's brought it up on the screen. after a 10 to 12 hour fast overnight didn't impair their muscle growth or performance at all. But there are some caveats. In older adults, calorie restriction can sap muscle strength and reduce energy for peak performance. So if your grandpa wants to win the Olympics, don't calorie restrict. And a 2025 study led by Andrew Galpin looked at 17 well-trained adults over eight weeks of resistance training four times a week. One group followed a 168 timerestricted eating pattern while training fasted in the morning and the control group ate in a normal spread out pattern. Both groups built upper and lower body strength and improved their muscular endurance and both gained
muscular endurance and both gained similar amounts of fat-free mass, but squat strength gains were slightly smaller in the timerestricted eating group and they reported feeling a bit less energized overall. So the bottom line is this. Fasting or calorie restriction don't automatically ruin your performance. If you're well hydrated and eating enough protein, you can maintain muscle and strength. The best approach is to monitor how you feel when exercising, fed or fasted, and track your performance and adjust. Now, women often ask me, "Is fasting the same for us as it is for men?" The short answer is no. Women's hormone levels can vary during the month unless they're postmenopausal. Okay, let's pull up a graph of this. As you can see, in the first half of the menstrual cycle, when estrogen is higher, many women find they can tolerate longer fasts really well. But in the second half of the menstrual cycle, during the lutil phase, when progesterone dominates, cravings, fatigue, and stress often increase, so longer fasts can feel even harder. So, you might want to time your fasts for the first half of the menstrual cycle and go easier in the second half. Also, if you're trying to conceive or if you're pregnant or even breastfeeding, it's especially important to check in with your doctor before changing your diet. Another common question I get is, "I've hit a plateau. Now, what should I do?" We've all been there. Weight stalls, progress slows, so here's how I troubleshoot. First, I tighten my eating window. Even an extra hour or two of fasting can make a big difference. Second, I adjust my training with progressive overload, lifting a little bit heavier than usual. I also try moving more or using my standing desk more often. Even just taking meetings while walking is a great thing to do. So, thirdly, I check my food quality. Sometimes I find that bad food is crept into my diet. So, ask yourself, am I still getting enough fiber, protein, and water? Fourthly, I check my blood work. If things are really not changing, maybe
If things are really not changing, maybe I'm low on vitamin D, maybe my hormones are out, or I'm deficient in iron. Many things can mess with your metabolism. And finally, I check my sleep and stress. Both can block progress, even if everything else is right. So remember, plateaus aren't failure, they're just feedback. So use them to recalibrate. And sometimes people ask me, "Well, David, isn't this really expensive with your monitors and supplements and scales?" Well, that's true. You don't have to use all those things. If you're eating less, you're actually saving money on food. At the end of the day, your health span is always cheaper than disease. And fasting in its simplest form is actually free. So, naturally, people wonder, won't calorie restriction or fasting affect my family or my social life? And that's fair to ask. I thought that might happen, too. But actually, cutting back on calories at a restaurant, not finishing a meal, taking a bit home, it's no big deal. And when it comes to drinking, cutting back on alcohol, initially my friend said, "Come on, David, you got to drink." But if I just choose non-alcoholic beverages, they're totally fine with it. And with calorie restriction, it's often just about eating smaller portions, not skipping meals entirely. So, don't be rigid. The goal isn't to emotionally starve yourself. It's to make this work with your life, not against it. And the last question for this episode, and one that I love, is, can calorie restriction or fasting help my pet? The answer is yes. Just like us, pets benefit from eating a little less. In fact, scientists at Nestle in the 2000s showed that Labrador Retrievers on 25% calorie restriction diets lived much longer. They got arthritis later as well, and they died from cancer much later than those fed normally. So, if you're a pet owner, consider feeding your pet a little less often. But, of course, first talk to your vet to make sure it's okay. All of this is a powerful reminder that biology respects moderation. You want to put you or your pet into survival mode, and the way to do that is to not always
and the way to do that is to not always be fed. It's true not just in us, but across species. So, what does the future look like? Well, right now, we've got continuous glucose monitors, ketone breath sensors, and even AI powered meal timers. And these are just the beginning. Soon we might be using digital twins for personalized predictive medicine. A digital twin is essentially a virtual version of you. Built from your medical history, blood tests, genetics, lifestyle, even your gut microbiome. And one day, these twins will hopefully be able to predict disease and test hypothetical lifestyle changes and design personalized health plans. Imagine going to sleep and waking up to a message from your digital twin. Here's your optimal menu for today. Here's when you should eat. Imagine ordering takeout from an app that already knows all your needs. That future is closer than we think. We could also see designer gut bacteria. Microbes engineered to release satiety hormones or short-chain fatty acids on demand. Sort of like an internal fasting switch built right into your microbiome. Add to that even better epigenetic clocks and devices that can read your health a thousand times a second and predict diseases decades ahead. All of these and more could allow doctors or your AI nutritionist to recommend a fasting or a CR plan. That is exactly what you need. So, we've now walked through the science of CR and fasting. We've talked about how to implement them safely and how to track your progress and even where this field is headed. But always remember, listen to your body and celebrate the wins. More energy, better sleep, cleaner skin, looser clothes. In future episodes, we'll dig deeper into supplements, sleep, wearables, and some of the big debates, including protein intake, red meat, and medications that might mimic CR just like the GLP-1 [music] weight loss drugs. I'll unpack the science, set the record straight, and help you make
the record straight, and help you make sense of it all. Stay tuned. It's been great to have you with us. This is a show where science and evidence come first. The team works hundreds of hours to bring you [music] only the facts. To learn more and to join our community, visit lifespan. com and you'll get early access to future episodes, to the Lifespan magazine, and to detailed episode show notes. You also get transcripts and links to the papers that we talked about today. As a member, you'll actually be helping us support medical research to extend all of our healthy lives. If you found this episode valuable, do consider subscribing and also turn on your notifications [music] so you don't miss new episodes. It'll also help us make a better show for you. And feel free to share this episode with any family or friends who you think might enjoy it and learn from it. Finally, for the latest discoveries in longevity science, consider following us on Instagram at lifespan and onx at join lifespan. From all of us at lifespan, thank you for being part of this growing community. And remember, life's short, so let's change that together. Lifespan is produced by Andrew the wonderman Ying Rajie Geek Me Out Romesh Marissa who's on first vulgore Kathleen TLDDR Fitzgerald and our researchers Shiovani just one more thing Sethi and Adiv meet me in the year 3000 Johnson also I want to mention our new recruit Daniel Rocket Man Salazar who's our new producer and of course Serena my honeypoon I also want to thank Inspirro Studio and Create ape for making this [music] show possible possible And finally, thanks to our partners for helping us support Longevity Research. We'll see you next time. This show is forformational purposes only and is not medical advice. Please consult a qualified healthcare provider
consult a qualified healthcare provider as individual results may vary. Views expressed are my own and not those of Harvard University or Harvard Medical School. Full disclaimer is in the show notes.
Transcript auto-generated by YouTube. Verbatim — duplicates intentionally preserved.
The body does not process food in isolation. Meals arrive into a circadian system that changes insulin sensitivity, digestion, hormones, and repair across the day.
When eating patterns align with rhythm, metabolism has a clearer conversation with time.
Time-restricted eating and fasting can support metabolic flexibility for some people, but the details matter: health status, training load, stress, sleep, age, and body composition all change the context.
The aim is not restriction for its own sake. It is giving the body space to regulate and repair.
When to eat matters most when paired with what to eat. Protein, plants, healthy fats, fiber, and minimally processed foods remain the foundation.
Timing refines the signal. Quality supplies it.
The body reads both the meal and the moment it arrives.
Align most eating with daylight hours when possible, while respecting training, work, and health needs.
Treat fasting as a flexible tool and avoid using it to override hunger, stress, or recovery signals.
Keep food quality central: protein, fiber, colorful plants, and minimally processed meals.
