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

**Andrew Huberman** (0:00)
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. 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 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. 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. We are going to emphasize again whether or not the study was done in mice or in humans, in athletes, in men and 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. 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 2000 calories per day. So their quote unquote 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 sextoid hormones, testosterone and estrogen, those levels will also profoundly influence the calories 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 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 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 and 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. 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 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. 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 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. 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. 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. 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.