Essentials: Effects of Fasting & Time Restricted Eating on Fat Loss & Health

In this Huberman Lab Essentials episode, I explore intermittent fasting and time-restricted eating, highlighting the positive benefits for weight loss, metabolism, organ health, circadian rhythms and cellular repair. I explain a practical framework for designing a time-restricted eating window that aligns with your lifestyle, exercise schedule and social schedule. I also cover what breaks a fast, how to support fasting with tools like salt intake and post-meal walks, and the use of fasting-related supplements, including berberine and metformin. Read the episode show notes at hubermanlab.com. Thank you to our sponsors AG1: https://drinkag1.com/huberman Carbon: https://joincarbon.com/huberman LMNT: https://drinklmnt.com/huberman Joovv: https://joovv.com/huberman Timestamps (00:00) Intermittent Fasting, Time-Restricted Eating (TRE) (00:50) Diet, Weight Loss, Calories & Hormones (05:50) Body’s Response to Eating vs Fasting, Fasting Duration (09:04) Sponsor: Carbon (10:50) Time-Restricted Feeding & Metabolic Benefits, Circadian Gene Rhythm (16:19) Optimal Meal Timing, Tool: Extend Sleep-Related Fasts (21:29) Sponsors: AG1 & LMNT (24:02) Eating Window Length, Tools: Adjusting TRE for Building Muscle, Regularity (26:55) Accelerate Transition to Fasting, Glucose Clearing, Tool: After-Meal Walk (28:36) Metformin, Berberine, Continuous Glucose Monitors; Cell Growth vs Repair, mTOR (31:46) Gut Microbiome; Transitioning to Intermittent Fasting & Individualization (34:03) Tool: 8-Hour Feeding Window & Weight Loss (35:25) Sponsor: Joovv (36:40) What Breaks a Fast?, Sugar; Tool: Using Salt to Support Fasting (39:42) Tool: Ideal Feeding Window Guidelines; Exercise & Social Considerations Disclaimer & Disclosures Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Andrew D. Huberman?

  Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. What we're going to talk about today is how intermittent fasting, aka time-restricted feeding, impacts weight loss, fat loss in particular, muscle maintenance and loss and gain, organ health, such as gut health and liver health, the genome, the epigenome, inflammation, sickness, recovery, and healing from sickness, exercise, cognition, mood, and lifespan.

• 0:43Andrew D. Huberman?

  So let's talk about eating and what happens when you eat, and let's talk about fasting, or not eating, and what happens when you fast. If ever there was a topic that is controversial, especially on the internet, it is that of diet and nutrition. So I'm wading into this with a smile and in eager anticipation of all the "but, but, but this", and "but, but that", and "wait, but this showed that". Here's the deal. We need to precisely define what it is that we're talking about when we talk about nutrition. I'm going to give you an example of a study that was published a few years ago, 2018, by a colleague of mine at Stanford, Chris Gardner. He's a terrific professor of nutrition

• 1:27Andrew D. Huberman?

  and has done a lot of important studies on how nutrition impacts different aspects of health. This paper, where Chris is the first author, it's Gardner et al., 2018, JAMA, looked at weight loss in people following one particular diet versus another particular diet. And this was a 12-month weight loss study. So it was focused specifically on weight loss, although they looked at some other parameters as well. And the basic conclusion of the study was that there was no significant difference in weight change between people following a healthy, low-fat diet versus a healthy, low-carbohydrate diet with significantly more dietary fats in them.

• 2:10Andrew D. Huberman?

  This caused a lot of ripples in the world of nutrition and nutritional science, and certainly in the general population. Because anyone that understands diet and nutrition would immediately say, "But wait, there are all sorts of different implications of eating one type of diet, say, low carbohydrate, higher fats, versus a higher carbohydrate, lower fat diet." And indeed, there are. This study was focused specifically on fat loss and on weight loss. So as we discuss time-restricted feeding, we need to be very precise about what are the effects of time-restricted feeding and of eating in particular ways at particular times.

• 2:52Andrew D. Huberman?

  We are going to emphasize, again, whether or not the study was done in mice or in humans, in athletes, in men, in women, or both. But the study from Gardner and colleagues is a beautiful study and really emphasizes that if one's main goal is simply to lose weight, then it really does not matter what one eats, provided that the number of calories burned is higher than the number of calories ingested. However, anyone out there who understands a little bit of biology, or a lot of biology, will agree that there are many factors that impact that calories burned part of the equation. Some of those are obvious.

• 3:33Andrew D. Huberman?

  So for instance, amount of exercise, type of exercise, basal metabolic rate, how much energy one burns just sitting there. I've talked before on this podcast about NEAT, non-exercise-induced thermogenesis, where if people bounce around a lot and fidget a lot, they can burn anywhere from 800 to 2,000 calories per day. So their "basal metabolic rate" is actually much higher simply because they're fidgeters, whereas people who tend to be more stationary have a lower basal metabolic rate on average. There's great science to support this. Metabolic factors and hormones are also very important. Hormones such as thyroid hormone and insulin and growth hormone and the sex steroid hormones, testosterone and estrogen, those levels will also profoundly influence the calories

• 4:18Andrew D. Huberman?

  out, the calories burned component of the calories in calories out equation. So if out there on the internet or in listening to a particular podcast or speaker, somebody says, "This is the ideal diet," or "calories in calories out does not matter," or "calories in calories out is the only thing that matters." I think it's very important to understand that there are some foundational truths such as calories in calories out, but that of course hormone factors and the context in which a given diet regimen is taking place are exceedingly important. So there's no way that we can drill into every aspect of a given feeding plan or feeding

• 4:59Andrew D. Huberman?

  schedule that would allow us to tap into every aspect of the list that I read out before, weight loss, fat loss, muscle, organ, genome, epigenome, inflammation, exercise, cognition, mood and lifespan. But today, we're going to be very precise about how time restricted feeding, it's very clear from both animal studies and human studies, can have a very powerful and positive impact on everything from weight loss and fat loss to various health parameters. This is a beautiful literature that's emerged mostly in the last 10 or 15 years. So there is a perfect diet for you and today I'm going to arm you with the mechanisms and understanding that will allow you to define what that perfect diet is and will

• 5:43Andrew D. Huberman?

  allow you to eat on a schedule and to eat the things that are going to best serve your goals. Some simple rules about eating. First of all, when you eat, typically your blood glucose, your blood sugar will go up. Also, insulin levels will go up. Insulin is a hormone that's involved in mobilizing glucose from the bloodstream. How much your glucose and insulin go up depends on what you eat and how much you eat. In general, simple sugars, including fructose from fruit, but also sucrose and glucose and simple sugars, will raise your insulin and blood glucose more than complex carbohydrates, things like grains and breads and pastas and so forth.

• 6:28Andrew D. Huberman?

  And grains and breads and pastas and so forth will raise your blood glucose more than fibrous carbohydrates like lettuce and broccoli and things of that sort. Protein has a somewhat moderate or modest impact, and fat has the lowest impact on raising your blood glucose and blood insulin. So, what you eat will impact how steep a rise in blood glucose and insulin takes place, and there are a number of factors that are related to your individual health that will also dictate how steep and how high that rise in glucose and insulin will be. The longer it's been since your last meal, the lower typically your blood glucose and

• 7:08Andrew D. Huberman?

  insulin will be, and the higher things like GLP-1, glucagon-like peptide 1, glucagon being a hormone that's also secreted when you are in a fasted state or a low blood glucose state. It's involved in mobilizing various energy sources from the body, including fat through what we call lipolysis, also using carbohydrates, and potentially even using muscle as a source of energy. So, that's kind of a fire hose of information about what happens when you eat and don't eat, but just think of it this way: blood sugar and insulin go up when you eat, they go down when you don't eat, and other hormones go up when you don't eat.

• 7:51Andrew D. Huberman?

  So there are hormones associated with the fasted state, and there are hormones associated with the eating and having just eaten state. Now, the most important thing to understand is that...

• 8:05Andrew D. Huberman?

  Like everything in biology, this is a process that takes time. So insulin and glucose go up when we eat, and it takes some period of time for them to go down. Even if we stop eating, they will remain up for some period of time and then go back down. It takes time. This is very important because if you look at the scientific literature on fasting, on time-restricted feeding, it's absolutely clear that the health benefits, not just the weight loss benefits, but that the health benefits from time-restricted feeding occur because certain conditions are met in the brain and body for a certain amount of time.

• 8:46Andrew D. Huberman?

  And that gives us an anchor from which to view what eating is in terms of how it sets conditions in the body over time. And if that sounds overly analytic, I promise you, this is the simplest and best way to think about any eating schedule or any eating plan. I'd like to take a quick break and acknowledge one of our sponsors, Carbon. Carbon is a diet coaching app built by nutrition expert Dr. Lane Norton. I've used Carbon for more than three years now, and I have to say, having been interested in fitness and in my nutrition for more than three decades, it's among the most powerful tools for nutrition coaching and effective weight management that I've ever encountered, especially if your goal is like mine, which is to maintain or build muscle while also losing fat.

• 9:30Andrew D. Huberman?

  Now, I'm turning 50 years old this September, and even though I consider myself in pretty good shape, and I've been training for a long time and trying to eat right, one of my goals is to hit 50 in the absolute best shape of my life. To do that, I'm dialing in my nutrition using Carbon with the goals of increasing my muscle mass, increasing my strength, while also decreasing my body fat. I've been raving about the Carbon app to friends and to family and to members of my Huberman Lab team over the last few years. And everyone who's joined me in using it has found it to be tremendously useful. In fact, some of those people are going to join me in my approaching 50 fitness goals and body composition goals. My birthday is September 26th, and so I'd like to invite you to join, if you would like to improve your body composition and fitness, to also use the Carbon app.

• 10:14Andrew D. Huberman?

  Now, there are a lot of apps out there that are focused on fitness and nutrition. But what makes Carbon different is that it doesn't just hand you a one-size-fits-all plan. It actually learns your metabolism over time and it adapts your program based on your results. So if you're looking to take a smarter, more personalized approach to your nutrition, I can't recommend the Carbon app enough. To try Carbon, you can go to joincarbon.com/huberman. While Carbon does not typically offer trials or promotions, they've agreed to give a free seven-day trial to all Huberman podcast listeners. Again, that's joincarbon.com/huberman to get a seven-day free trial. So I think it's fair to say that in the field of nutrition, there are a few landmark

• 10:55Andrew D. Huberman?

  studies that serve as really strong anchors for building our understanding of what to eat and what not to eat and when to eat depending on our goals. The Garner study that I mentioned earlier is one such study in that it says if your goal is weight loss, it really does not matter what foods you consume, provided that you consume a sub-maintenance caloric diet. However, I want to emphasize again, that sets aside issues of adherence, meaning how easy or hard it is to adhere to a given diet. Some people find it much easier to follow a high-fat, low-carbohydrate diet. Some people follow a different diet because it's much easier for them to follow. And some people are concerned with mental performance and athletic performance.

• 11:40Andrew D. Huberman?

  So that study doesn't say there's a best diet. What it says is that what you consume is less important than the amount of food that you consume, at least for sake of weight loss, not necessarily for sake of health. Now, the study that I'm going to refer to next is what I would consider the second major pillar of nutritional studies. This was a paper in mice that set the basis for studies in humans that came later. And the title of this paper is "Time-Restricted Feeding Without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet." So the title tells us a lot.

• 12:19Andrew D. Huberman?

  It says that what's varied in this study is not what these mice ate, it was when they ate it. One of the most important things to take away from this study was that mice that ate a highly palatable, high-fat diet, a great tasting diet, but only during a restricted feeding window of each 24-hour cycle, maintained or lost weight over time. Whereas mice that ingested the same diet, same amount of calories...

• 12:47Andrew D. Huberman?

  But had access to those calories around the clock, gained weight, became obese and quite sick. And as an additional second point, the mice that restricted their feeding window to a particular portion of eight hours of every 24-hour cycle actually showed some improvement in important health markers. And what was even more incredible is that mice that only ate during a particular feeding window also experienced some reversal of some prior negative health effects. Not only did restricting food to a particular phase of the 24-hour cycle benefit things like lean body mass and fat loss and a number of health parameters

• 13:32Andrew D. Huberman?

  that I'll talk about in a moment, but it also anchored all the gene systems of the body and provided a more regular, stable, so-called circadian rhythm or 24-hour rhythm. You may be surprised to learn that 80%, 80% of the genes in your body and brain are on a 24-hour schedule. That is, they change their levels, going from high to low and back to high again across the 24-hour cycle. And when those genes are high at the appropriate times and low at the appropriate times, meaning their expression is high and low at the appropriate times, and therefore, the proper RNAs and proteins are made, because DNA encodes for RNA. RNA is translated into proteins.

• 14:16Andrew D. Huberman?

  When that happens, your health benefits. When those genes are not expressed at the right times, when they're high or low at the wrong times of each 24-hour cycle, that's when you get negative health effects. And while this was in mice, we now know that this also occurs in humans. So if you want to be healthy, you want your organ health, your metabolic health, to be entrained properly, one of the most important things you can do is to eat at the appropriate time of each 24-hour day. When mice can eat around the clock, bad things happen. And one of the bad things that happens is that the liver suffers. Fatty deposits in the liver, other factors in the liver, essentially taking down the pathway of liver disease.

• 14:59Andrew D. Huberman?

  The time-restricted feeding essentially reversed that or led, in many cases, to an even healthier liver condition. So restricting your feeding to a particular window every 24-hour cycle has clearly been shown now in mice and in humans to enhance liver health, which is wonderful.

• 15:18Andrew D. Huberman?

  How does it do this? Well, it happens because food intake, as I mentioned earlier, sets certain conditions in the body that last for a period of time. Anytime we eat, there's a period of time that's required for so-called digestion, but also gastric emptying and other processes related to breaking down that food and utilizing it. That process of breaking down food involves certain cellular functions that if they're ongoing throughout the 24-hour cycle, or even extended too far across the 24-hour cycle, meaning you're eating across a 14-hour, or a 16-hour, or an 18-hour window, that causes serious problems. So by eating around the clock, you're making yourself sicker.

• 16:01Andrew D. Huberman?

  By eating at restricted periods of time each 24-hour day, you're actually making yourself healthier and you're activating certain processes that can positively impact both weight, either maintenance or loss of weight, and blood glucose regulation. As we move forward and we talk about intermittent fasting, I want to start to establish a foundational protocol that all of us, any of us, can use in order to maximize your particular goals. There are some absolutes within this realm of time-restricted feeding. Here are a couple of absolutes that you would want to consider. First of all, it pays off, in the metabolic sense and in the health sense

• 16:46Andrew D. Huberman?

  and in the weight maintenance or loss sense, to not ingest any food in the first hour after waking, and potentially for longer. The second major pillar, that's well-supported by research, is that for the two and ideally three hours prior to bedtime, you also don't ingest any food, or liquid calories for that matter. So let's deal with this first question of when is the ideal feeding window? And here again, we're thinking about a schedule of eating that involves eating at least once every 24 hours, not two-day, or three-day, or every other day fast. So it turns out that the answer to the question, "When is it best to eat?",

• 17:28Andrew D. Huberman?

  is actually best answered by thinking about the other side of the coin, which is, "When is it best to fast?" So because we are fasting during sleep, it's very clear that it's best to extend the sleep-related fast.

• 17:44Andrew D. Huberman?

  Either into the morning or to start it in the evening. Now, this might seem kind of obvious, but it's actually not so obvious. You could place that feeding window early in the day, middle of the day, or late in the day. Let's think about what happens when we sleep. When we sleep, our body undergoes a number of different processes in the brain and body in order to recover the cells and tissues. Many of you have probably heard of autophagy, which is essentially a cleaning up, a gobbling up of dead cells and cells that are injured or sick. And this is a natural process that occurs, and it occurs mainly during sleep, although not only during sleep.

• 18:25Andrew D. Huberman?

  Fasting of any kind does tend to enhance autophagy. So when we're asleep, the bad cells are getting gobbled up and eaten, and the good cells also are undergoing certain repair mechanisms mainly related to, or at least governed by, those circadian genes that we talked about earlier, those clock genes. So one thing is certain, that you want your eating window to be tacked or attached to your sleep-based fasting in a way that makes it easier for you to get into the fasted state for a period of time. Now, most people find it very hard to only eat in the middle of the day. So while that's best, it's ideal for sake of the fasting-related improvements in health,

• 19:08Andrew D. Huberman?

  it is not ideal, and it's not very applicable to most work and family and social situations. Most people eat breakfast with others and/or eat dinner with others. But in general, it's hard to restrict your feeding window to just the absolute middle of the day. But from a purely health perspective, in a very objective way, that would be the ideal situation. It does appear beneficial to grab a hold of that sleep-related fast, meaning you don't want your feeding window to be too close to bedtime. And that's why we came up with this kind of foundational pillar, which is at least no eating for the first hour after waking, but also no eating within two to three hours prior to bed.

• 19:53Andrew D. Huberman?

  So from both a practical and a health perspective, and a purely objective view of how intermittent fasting works and can benefit us. Starting to eat each day somewhere around 10 a.m. or around noon, and then allowing a feeding window that goes until 6:00 or maybe 8:00 p.m. That seems to me like the kind of schedule that will allow you to get the most out of intermittent fasting, time-restricted feeding, but does not set you up to be really out of sync with the social rhythms in most cultures. If you think about it, from the perspective of, say, a noon to 8:00 feeding window, what

• 20:37Andrew D. Huberman?

  you'll find is that you're able to eat lunch with others, if you like, or by yourself. You will be able to eat dinner at a reasonable hour, at least in most countries and most cultures, eating dinner somewhere between 6:30 and 7:00 p.m. is typical. When you say a feeding window that goes until 8:00, that doesn't mean sitting down to dinner at 8:00. That means your last bite of food or ingestion of any liquid calories was at 8:00 p.m. Assuming that you go to bed somewhere between 10:00 p.m. and 1:00 a.m., that allows this tapering off or this transition from feeding to a fasted state and still allows you to capitalize on the special period of fasting that is sleep-related fasting.

• 21:20Andrew D. Huberman?

  And again, I want to emphasize that the fasting that occurs during sleep is vital, and eating too close to sleep will disrupt that fasting-related sleep. I'd like to take a quick break and acknowledge our sponsor, AG1. AG1 is a vitamin-mineral probiotic drink that also includes prebiotics and adaptogens. As many of you know, I've been taking AG1 for more than 13 years now. I discovered it way back in 2012, long before I ever had a podcast, and I've been drinking it every day since. For the past 13 years, AG1 has been the same original flavor. They've updated the formulation, but the flavor has always remained the same. And now, for the first time, AG1 is available in three new flavors: berry, citrus, and tropical. All the flavors include the highest-quality ingredients in exactly the right doses to

• 22:04Andrew D. Huberman?

  together provide support for your gut microbiome, support for your immune health, and support for better energy and more. So now, you can find the flavor of AG1 that you like the most. Well, I've always loved the AG1 original flavor, especially when I mix it with water and a little bit of lemon or lime juice. That's how I've been doing it for basically 13 years. Now I really enjoy the new berry flavor in particular. It tastes great and I don't have to add any lemon or lime juice. I just mix it up with water. If you'd like to try AG1 and these new flavors, you can go to drinkag1.com/huberman to claim a special offer. Right now, AG1 is giving away an AG1 Welcome Kit that includes five free travel packs and a free bottle of vitamin D3K2. Again, go to drinkag1.com/huberman to claim the special Welcome Kit of five free travel packs

• 22:48Andrew D. Huberman?

  and a free bottle of vitamin D3K2. Today's episode is also brought to us by Element. Element is an electrolyte drink that has everything you need, but nothing you don't. That means the electrolytes, sodium, magnesium, and potassium, all in the correct ratios, but no sugar. Proper hydration is critical for optimal brain and body function. Even a slight degree of dehydration can diminish cognitive and physical performance. It's also important that you get adequate electrolytes. The electrolytes, sodium, magnesium, and potassium, are vital for the functioning of all the cells in your body, especially your neurons or your nerve cells. Drinking Element dissolved in water makes it extremely easy to ensure that you're getting adequate hydration and adequate electrolytes. To make sure that I'm getting proper amounts of hydration and electrolytes,

• 23:31Andrew D. Huberman?

  I dissolve one packet of Element in about 16 to 32 ounces of water when I wake up in the morning and I drink that basically first thing in the morning. I also drink Element dissolved in water during any kind of physical exercise that I'm doing. They have a bunch of different great tasting flavors of Element. They have watermelon, citrus, et cetera. Frankly, I love them all. If you'd like to try Element, you can go to drinkelement.com/hubermanlab to claim a free Element sample pack with the purchase of any Element drink mix. Again, that's drinkelement.com/hubermanlab to claim a free sample pack. The important thing here is to establish a feeding window that you can comfortably manage, okay? Meaning that on average, you can obey an eight-hour feeding window or a 10-hour feeding window. And then to place that feeding window

• 24:15Andrew D. Huberman?

  in a social and life context that you can manage on a regular basis. Now, there are two key points that have been gleaned from the scientific data about this feeding window and when to place it. First of all, we can say is that the seven to nine-hour feeding window produces all of the major health benefits of time-restricted feeding. As well as being pretty straightforward for most people to adhere to on a regular basis. And on a regular basis turns out to be very important. I'll get back to that point in a moment. Whereas the four to six hour eating window doesn't seem to serve people as well as say, a seven or eight hour eating window, simply because people are overeating during that eating window. So let's talk about some conditions where having the feeding window early in the day

• 25:00Andrew D. Huberman?

  would actually be very beneficial. If your main interest is maintaining and/or building muscle, then it can be beneficial to ingest protein early in the day. You would still want to obey this, what we're calling a kind of foundational rule of not eating any food for the first hour post-waking. And the cutoff for when you would want to eat protein would be sometime before 10:00 a.m. And there I'm averaging across a number of different situations. Now, it's not as if at 10:01 a.m. a gate slammed shut and you can't generate hypertrophy. Of course, that's not the case. However, it's very interesting that it doesn't matter when the resistance training, the

• 25:42Andrew D. Huberman?

  load-bearing exercise occurs in the 24-hour cycle. So whether or not, in other words, people are training early in the day or they're training late in the day, it still appears that ingesting protein early in the day favors hypertrophy. So obviously, we don't want to be overly neurotic about this stuff, but because this is an episode about the science of intermittent fasting and time-restricted feeding, as important as how long your feeding window is, is where that feeding window resides in each 24-hour cycle. And perhaps even more important than that is that it be fairly regular where that feeding window resides. Because even if you have a very short feeding window, if it's drifting around from day

• 26:24Andrew D. Huberman?

  to day, that actually offsets a number of the positive health effects of intermittent fasting. Along those lines, however, there are things that we can all do that will allow us to offset some of the drift. If you will, that we experience or that we induce in terms of when our feeding window occurs, or that the feeding window might push out a little later and then therefore start a little later the next day. There are things that we can do and there are things that we can take. And so I'd like to discuss those briefly. So throughout this episode, I've more or less been alluding to the fact that when you eat, there's some period of time afterwards in which you're actually still eating, at

• 27:05Andrew D. Huberman?

  least from the perspective of metabolism, because glucose is up, insulin is up, and you're undergoing different metabolic and digestive processes that don't really speak to you being in a fasted state, right? It's not just about when you take your last bite or your last sip. However, there are things that we can do to accelerate the transition from a fed state to a fasted state. And so I'd like to discuss what those are. So there's a fun and exciting concept, which is glucose clearing. You may have heard the old adage that if you take a 20 or 30 minute walk after dinner, that it accelerates the rate at which you digest that food. And indeed, it does. So for instance, if you were to

• 27:50Andrew D. Huberman?

  eat a meal that ended at 8:00 PM and then plop to the couch, it would be five or six hours until you have transitioned from a fed state to a fasted state. However, you can accelerate that considerably by taking a 20 or 30 minute just light walk. And this gets back to this key feature of our biology, which is that what we eat, when we eat, when we exercise, when we view light, it's about setting a context or a set of conditions in your brain and body. So it's not so much about the activities that you undergo, it's about the activities you undergo and their relationship to one another over time. And so in this way, it really beautifully highlights the way that your biology is interacting all

• 28:35Andrew D. Huberman?

  the time. Now, there are other ways to clear out blood glucose. That involve supplements or prescription drugs. These are so-called glucose disposal agents. Glucose disposal agents such as metformin, which is a prescription drug, or berberine, which is an over-the-counter substance, will lead to very dramatic reductions in blood glucose. Now, I've tried berberine before, and what I can tell you is that if you take berberine, which by the way is very much like metformin, its effects are almost identical to metformin in fact, but it's much less expensive and it's over the counter. If you take berberine and you have not ingested carbohydrates, many people, including myself, experience a splitting headache.

• 29:18Andrew D. Huberman?

  You become hypoglycemic because it is a glucose clearing agent. Nowadays, there are a number of commercially available continuous glucose monitors. I've tried one of these. It involves putting what's essentially a patch with a little needle that goes into your skin, which is continually monitoring your blood glucose, and you can look at it at an app on your phone. And you can learn a lot that way about how different foods impact the increases and decrease in blood glucose. If you're doing experiments with berberine or metformin, you can see how those impact your blood glucose. You can see how exercise, HIIT training, or otherwise impacts blood glucose. Excuse me again. I have to say that glucose clearing agents that involve a walk or exercise, moderate or intense,

• 30:02Andrew D. Huberman?

  are going to be a lot easier to titrate and adjust the levels of than things that you're going to take where you have to ingest the dosage, and then, once you ingest a certain dosage, you're along for the ride, at least until the effects of that particular compound wear off. In the fasted state, a number of different proteins that are expressed in cells undergo changes in their expression. When we are fasted, we tend to reduce the activity of a particular protein called mTOR, mammalian target of rapamycin. mTOR is very active in cells while they are growing. So, one way I'd like you to think about the fed state is that when you eat or when you don't eat, when you're fed, when you're fasted, you are either promoting cellular growth of all kinds,

• 30:45Andrew D. Huberman?

  or you're promoting cellular repair and clearance of all kinds. And so again, this is about setting conditions in the brain and body. It's not so much about when you eat food A or B, it leads to increases in mTOR. Anytime you eat any food, doesn't matter if it's plant-based, animal-based, fat, protein, carbohydrate, doesn't matter, you are biasing your system towards a biochemical state of cell growth. And anytime you haven't eaten for a while, or blood glucose is low, you're biasing your system toward a state of cellular repair. And this is why people who do not suffer from any blood glucose regulation issues, take things like berberine as glucose disposal agents, or take metformin.

• 31:29Andrew D. Huberman?

  I'm not necessarily suggesting that you do that, but it's because those things mimic fasting. They create situations in the body that promote things like AMPK and the sirtuins and others to push your body and your system down a route of repair, even though you might have just eaten a meal an hour ago. Along the lines of the health benefits of intermittent fasting, there are nice data showing improvements in the gut microbiome, and in particular, in the treatment of irritable bowel syndrome and other forms of colitis. It appears that intermittent fasting can reduce the amount of so-called lactobacillus that's present in the gut. And lactobacillus is, when in high levels, is correlated with a number of different metabolic

• 32:14Andrew D. Huberman?

  disorders. At the same time, time-restricted feeding seems to enhance the proliferation of some of the gut Microbiome like osilobacter, and some of the other ones that promote healthy mucosal lining and that promote better overall intestinal function. There are some data that point to differences in the effects of intermittent fasting for males versus females. Those data right now only come from mice. That study was published by Sachin Panda recently. We still await the studies in humans. Some people do not do well on intermittent fasting, either in terms of mood or hormone health. And so everyone needs to determine for themselves whether or not having a time-restricted feeding

• 32:56Andrew D. Huberman?

  window is good for them, how long that time-restricted feeding window should be. I think eight hours is kind of a nice minimum to adhere to, based on everything that we've covered today. And for some people...

• 33:08Andrew D. Huberman?

  Time-restricted feeding is not going to be compatible with hormone health for them. For them, eating more meals spread throughout the day, presumably smaller meals, same caloric intake, is going to be more beneficial for their hormones. This is something that is going to be individual and is going to have to be determined on an individual basis. However, if you're going to try time-restricted feeding, I do want to remind you that taking a period of three to seven, or ideally 10 days, to transition into it, not just going, flipping from eating to three meals a day that span from 6:00 a.m. to 10:00 p.m. and suddenly going to an eight-hour feeding window, but rather winnowing down that feeding window about an hour or so per day is going to allow the hormone systems of your body, including leptin, the hypocaloric system, which are systems within the body

• 33:51Andrew D. Huberman?

  that signal to the brain that food is about to come, allowing those systems to adjust so that you're not overwhelmingly hungry, irritable, and you're not throwing your whole hormone system out of whack. I keep coming back to this eight-hour feeding window, and I want to provide a little more basis for it, and just to encourage that it's not completely arbitrary. There's a particular study that I'd like to highlight, mainly because I don't expect people to delve into the full reference list of the other review. And this is a study that was carried out between Sachin Panda's lab and Krista Verardi's lab. So this is a collaboration. The study was carried out in humans and is entitled, "Effects of Eight-Hour Time-Restricted Feeding on Body Weight and Metabolic Disease Risk Factors in Obese Adults." Excuse me.

• 34:35Andrew D. Huberman?

  And this study essentially showed, I'll just read the conclusions, that an eight-hour time-restricted feeding produces a mild caloric restriction and weight loss without calorie counting. So that's key, right? These people aren't calorie counting. Somehow, just by adhering to an eight-hour window, they are taking in fewer calories than they're burning off, and clinically, it reduced blood pressure. So I mention this study not because there aren't many others involving the eight-hour feeding window also in humans, but because the eight-hour feeding window has been tested in obese adults and non-obese adults, and there are even a few studies in children. So this eight-hour window seems to be a really good rule of thumb

• 35:19Andrew D. Huberman?

  and a kind of anchor around which we can each think about. Incorporating time-restricted feeding. I'd like to take a quick break and acknowledge our sponsor, JOOV. JOOV makes medical-grade red light therapy devices. Now, if there's one thing that I have consistently emphasized on this podcast, it's the incredible impact that light can have on our biology. Now, in addition to sunlight, red light and near-infrared light have been shown to have positive effects on improving numerous aspects of cellular and organ health, including faster muscle recovery, improved skin health and wound healing, improvements in acne, meaning reductions in acne, reduced pain and inflammation, improved mitochondrial function, and even improving visual function itself. What sets JOOV lights apart and why they're my preferred red light therapy device is that they use clinically-proven wavelengths,

• 36:04Andrew D. Huberman?

  meaning specific wavelengths of red light and near-infrared light in specific combinations to trigger the optimal cellular adaptations. Personally, I use the JOOV Whole Body Panel about three to four times per week, typically in the morning, but sometimes in the afternoon. And I use the JOOV Handheld Light both at home and when I travel. If you'd like to try JOOV, you can go to JOOV, spelled J-O-O-V-V dot com slash Huberman. JOOV is offering an exclusive discount to all Huberman Lab listeners with up to $400 off select JOOV products. Again, that's JOOV, J-O-O-V-V dot com slash Huberman, to get up to $400 off. Any discussion about fasting would be incomplete without a discussion about what does and does not break a fast.

• 36:47Andrew D. Huberman?

  Insofar as the scientific literature says, drinking water will not break your fast.

• 36:55Andrew D. Huberman?

  Drinking tea will not break your fast. Drinking coffee, provided it is black coffee, will not break your fast. Ingesting caffeine in pill form will not break your fast. There are other things that won't break your fast. For instance, eating one peanut when deep in a fasted state will not break your fast. However, if you just finished a meal that included carbohydrates or it was a very large meal of any kind an hour ago, yes, indeed, eating one peanut could break your fast. So it's all contextual. That's what's really important to understand. And unless you're going to wear a continuous glucose monitor and set an absolute numerical threshold for what it is to break your fast, I think there are some simple rules that we can follow.

• 37:41Andrew D. Huberman?

  First of all, anything that involves sugar, in particular, simple sugars, can potentially break your fast. For instance, if you drink a can of soda pop, unless you just ran an ultra marathon, you're breaking your fast, okay? Eat a piece of pizza, you're breaking your fast. So you can start to see where there's a lot of wiggle room and it's very contextual. Today, we've really bypassed the discussion about foods of a particular origin or type, animal-based or plant-based. But all the same rules apply within this thing that we're called intermittent fasting or time-restricted feeding. So what breaks a fast will depend. And what you want to eat or what you are willing to eat, that's a totally separate manner from when you eat.

• 38:25Andrew D. Huberman?

  But as we've established, when you eat is vitally important. There is one particular thing that one can ingest that can help manage psychologically and performance-wise through the fasting portion of the intermittent fasting and get you to your feeding window. And that's salt. Many people find that the kind of lightheadedness, the shakiness that's accustomed with having slightly low blood sugar can be offset by taking a half teaspoon or so of sea salt or even just a tiny pinch of salt and putting into some water and drinking it. What is it doing? How is it offsetting all this? Well, salt water actually has a mild effect

• 39:09Andrew D. Huberman?

  as a glucose disposal agent, but it has a stabilizing effect on blood volume. And so because sodium brings with it water and the so-called osmolarity of your blood and your body depends on the salt levels in your blood and brain and body. Many people find that if they're feeling shaky, they're feeling lightheaded, they can't concentrate, they think they need sugar or food, but what will actually remedy that is some salt. And all it requires really is a small pinch of salt, ideally Himalayan or sea salt, if you want to get fancy about it, but table salt would be fine. In a moment, I'd like to review the parameters of an ideal feeding schedule for you and give you the variables that you can plug into your lifestyle and your preferences.

• 39:53Andrew D. Huberman?

  So, first of all, you do not want to ingest food for at least, I want to emphasize, at least 60 minutes post-waking up. Second, you want to avoid ingesting any food for the two to three hours prior to bedtime. Remember that the sleep-related fasting is especially important.

• 40:20Andrew D. Huberman?

  Because of all the cellular repair processes that occur in the liver, in the gut, in the microbiome, in the brain, all over the body, and because of the way that that coordinates the expression of the clock genes that are then going to wick out and have many other positive effects on health, including weight and fat loss, but in addition to that, liver health, etc. An eight-hour feeding window as a target seems to be the best target feeding window. Shorter feeding windows of four to six hours tend to lead to overeating and potentially increases in weight. Regular placement of the eating window or feeding window every 24 hours is important.

• 41:05Andrew D. Huberman?

  You don't have to be absolutely rigid and neurotic about this, but you don't want it sliding around on the weekend so that it's starting two hours later and ending two hours later a couple of days a week. Because then you start to offset many of the positive health effects that have been demonstrated for time-restricted feeding.

• 41:24Andrew D. Huberman?

  When should that eight-hour window be placed within each 24-hour cycle? Well, let's talk about ideal. Ideal, if you really want to maximize all the health benefits of time-restricted feeding, you need to extend the fast around sleep on both sides. You would place it smack dab in the middle of the day. It would be a schedule in which you started eating, for instance, at 10:00 a.m. and you stopped eating at 6:00 p.m. An absolutely dreadful schedule for anyone that wants to have some semblance of a normal life, in my opinion. It's not really compatible with most schedules, although some people might be able to do it.

• 42:06Andrew D. Huberman?

  Of course, you have to take into consideration when you exercise, if you exercise. For instance, I like to exercise early in the day if I run, or if I do some moderate or light intensity exercise, regardless of what type of exercise it is. I have no trouble waiting until my feeding window kicks in around noon or even 2:00 PM. But if I do high intensity weight training, for instance, early in the day, or if I run sprints, and I do that at 7:00 AM or 8:00 AM, by 11:00 AM, I am very, very hungry, and it's hard for me to do other things, concentrate, etc. If you're one of these people, or you're somebody who really is trying to emphasize hypertrophy or maintenance of muscle,

• 42:47Andrew D. Huberman?

  then it does seem that ingesting protein early in the day is beneficial, that it can be more readily converted into muscle tissue. Another thing that we can add to this summary or key points related to time-restricted feeding is the use of glucose disposal agents and/or behaviors. If you find that you've eaten too close to a period of time in which you would prefer to be fasting, that's when a 30-minute brisk walk or even modest walk after eating can be beneficial. And then there are the things like metformin and berberine, and I mentioned earlier why you would want to approach those with the appropriate level of caution and figure out the dosages for you.

• 43:29Andrew D. Huberman?

  And for some people, the dosages will be zero milligrams is going to be ideal. I know we covered a lot of information today. I hope you learned a lot about time-restricted feeding. I hope you learned a lot about metabolism and energy and health, and how when you eat is as important as what you eat. And last, but certainly not least, thank you for your interest in science.

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