The Truth About Fasting: Separating Fact from Fiction

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When it comes to fasting, there's a lot of misinformation floating around in One of the most common mis is that fasting slows down your metabolism. But here's the truth. It all depends on how you fast. It all depends on how you fast. Long term fasting can have its drawbacks, like slowing down your metabolic rate as your body conserves energy or losing muscle. But when it comes to short term fasting, the opposite is often true. It can actually give your metabolism a boost. In today's episode, we're diving deep into the science behind fasting and metabolism. We're going to break down the differences between long term and short term fasting and we're going to explore how your body responds to each and we're going to debunk some of the biggest myths out there. So whether you're curious about intermittent fasting or time restricted eating, or just want to better understand how fasting impacts your hormones, your energy levels and overall health, well, this episode is packed with insights to help you make informed choices. Hi, I'm Dr. Mark Hyman and welcome to Health Hacks.

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So let's cut right to it. The first myth. Myth number one, fasting slows your metabolism. Well, many people believe that fasting slows your metabolism. And this might be true in some extreme cases, but the truth is it depends on the type of fasting you're doing. Long term fasting could have negative implications for your metabolism, but with short term fasting, the Opposite actually seems to be true. It actually seems to speed up your metabolism. So let's break it down. What is long term fasting? Well, long term fasts typically range from a full day to several days without food. Long term fasts have lots of benefits. It stimulates autophagy or cellular cleanup. It promotes the burning of fat, clean fuel instead of carbs for energy. And it can be super beneficial for weight loss, improving insulin sensitivity and lowering body inflammation. About 48 hours or more into a fast, your metabolism starts to shift. The body may start to conserve energy, which results in a downregulation of metabolism. Now this is an adaptive response to prolonged calorie restriction. But because your body doesn't know when your next meal is coming, your metabolism slows to conserve energy. Now why is long term calorie restriction a problem? Well, over time, long term calorie restriction without adequate nutrition causes your body to go into what we call starvation mode. And this puts stress on your body. In most cases. A little stress isn't a bad thing. It can actually be good thing, but prolonged stress is not necessarily good. Now there's a concept known as hormesis. This is kind of a good stress. It's basically a stress that doesn't kill you, but makes you stronger. And you get that with short term fasting, with exercise, a sauna, cold plunge, and that turns on all your longevity switches. Now, calorie restriction is a form of hormetic stress and it has its benefits. But there's also bad stress which occurs when we undergo this stress for too long and the slower metabolism could be the result. So what caused your metabolism to slow down during long term fasts during TALLY restriction? Well, hormones change, leptin and ghrelin change. During prolonged fast. Your body undergoes changes in the appetite suppressing hormone called leptin and the appetite stimulating hormone called ghrelin or ghrelin or however you want to say it, but basically that's the hormone. Leptin is a hormone that's produced by fat cells and helps regulate metabolism and hunger. Kind of tells you when you're full, when calorie intake is restricted, leptin levels go down. And that tells your body that energy stores are low. Now this is a good thing for people who have a common condition called leptin resistance, which is when you basically have too much food and your leptin levels go up and up and you become resistant to the effects of leptin. And when you do fasting, it actually makes your leptin sensitivity better, so you're not resistant to its effects, which makes you feel full. And then that stimulates the body's ability to regulate your appetite more naturally. It also improves insulin sensitivity and leads to weight loss. Now, in the long term, in non obese individuals, when you fast too long, it can result in a slowdown of your metabolic rate. And that means you're going to try to conserve energy because your body thinks you're starving. Well, ghrelin, which is the hunger hormone, will initially increase during fasting, making you feel hungry. Its job is to stimulate appetite and food seeking behavior, which is a good thing. When you're hungry, you're going to go looking for food. Now during longer fasts, more than a few days, then grain levels start to decrease. And studies examining three day fasts have found that 24 hour mean grain levels actually declined over the fasting period. In other words, you know, a lot of people who were fasting report a decreased hunger as you continue to fast. So you might be hungry the first few days and then after a while you're not hungry. Now when you're less hungry, you eat less and the body then adapts by slowing down your metabolism. Now another thing happens when you fast too long. Your thyroid doesn't work out so good. A slower metabolism is in large part related to your thyroid hormone levels. See, thyroid is the master control center of your metabolism. When you undergo long term fasts or calorie restriction for longer periods of time, it actually lowers your thyroid hormone production and therefore you're resting metabolic rate, meaning you burn less calories just sitting around. T3 is the active thyroid hormone and it plays a really important role in regulating your metabolism. During longer fasts. The body aims to conserve energy and the way it does that, it reduces the production of of the active thyroid hormone called T3. So you don't burn as many calories. That slows your metabolism. And your body can conserve energy and become more efficient at using those fewer calories. Now this is good. When we didn't have a lot of food around and we conserved energy and it was sort of built in to protect us from food scarcity, but we don't have that anymore. Now as your metabolism starts to slow down, the body becomes resistant to weight loss and then it makes it harder to continue losing weight without further reducing calories, you get kind of a plateau. Of course if you're not eating at all, your body's going to continue to waste and you'll starve and die. But if you calorie restrict initially you'll lose weight, but then you hit a plateau. Now it's a survival mechanism. It's going to help your body conserve energy in times of scarcity. Now short term fasting is good because it doesn't result in a slowed metabolism, it does the opposite. It actually boosts your metabolism. So what's short term fasting? Well, there are many different types of short term fasts. A few of the main ones include what we call intermittent fasting. Now that's an umbrella term for various fasting schedules where you alternate between periods of eating and fasting. There's a lot of different methods out there. There's something called the 168 method, which is 16 hours of fasting and 8 hours of eating. So let's say you eat between, let's say eight in the morning and four in the afternoon, right? And then you're done. And then you take the next 16 hours off and you go to bed and you sleep and you wake up and you eat. There's something called the 5:2 method, which is eating normally for five days and dramatically reducing your calories for two days. Or there's alternate day fasting, or you can do even shorter fasts like 12 to 14 hours. Now intermittent fasting focuses on more extended fasting periods, which may include skipping meals or limiting calorie intake for whole days. But I think the better way to think about this is what I call time restricted eating. And it's a specific form of intermittent fasting that emphasizes eating all your daily meals within a consistent window of time, like 8 hours, 10 hours, and fasting for the rest of the day, like 14 to 16 hours. Unlike other forms of intermittent fasting, time restricted eating focuses more on aligning eating with the body's natural circadian rhythms and ensures all meals are consumed within a set time frame. Each day you can do 1212 fasting, 12 hour feeding window where all your calories are consumed, followed by a 12 hour fasting period where food intake is restricted. So basically when be fasting after dinner from 8pm to 8am the next morning, I mean everybody could probably do a 14 hour fast. Basically you eat dinner, you finish at, let's say six o'. Clock. That means you can eat breakfast at eight o' clock the next morning. Calorie restriction is not a requirement. It can be a side effect of condensing your daily food intake to a shorter time window because you just don't have enough time to eat that many calories. And that's why time restricted eating is so popular. It helps you eat fewer calories, which then leads to weight loss without having to change your diet. But optimizing your diet quality leads to even more benefits. We're going to discuss that later. But there are some studies that show that regardless of what you eat, it works. But it works better if you eat more healthy food. Now, short term fasting can actually reset and even boost your metabolism when you do it correctly. It does this by supporting fat burning and by supporting metabolic health. And it modulates several fat burning hormones, especially insulin. Now, high insulin levels block fat loss, and it makes it harder to lose weight. And intermittent fasting can change that. Insulin is the fat storage hormone. And when you have a high insulin level, you can't lose weight, and the fat gets locked in the fat cells, so you can't even burn them. Research shows that intermittent fasting can help lower your fasting insulin, which is especially meaningful for those with prediabetes, type 2 diabetes, or those with underlying metabolic dysfunction. And that, my friends, applies to 93.2% of Americans. That means somewhere in that spectrum of mild insulin resistance to prediabetes to type 2 diabetes, 93.2% of Americans fall in that group, which is terrible. And most of us would benefit from listening carefully to this podcast and actually applying the principles here. And a big study, what we call meta analysis, which is a study of other studies, found that intermittent fasting reduced insulin levels by an average of 13 milliunits per liter in patients with metabolic syndrome. And that is a lot. Okay, that's a lot. A review of the literature found that intermittent fasting and alternate day fasting could reduce fasting insulin levels in pre diabetics by up to 31% after eight weeks. That's a good thing, because high insulin levels lead to heart attacks, strokes, cancer, dementia, obviously diabetes, eventually. Now, some studies have even shown that patients were able to reverse their need for insulin therapy just by therapeutic intermittent fasting when they're supervised by their doctor. I've seen this over and over. When people eat healthily, when they cut out sugar and carbs, when they narrow their eating window to 12 minimum, but ideally 14 to 16 hours, it has dramatic effects. The other thing that happens when you do intermittent fasting is you increase the level of something called norepinephrine, kind of like adrenaline, right? This is your stress hormone. It's involved in the fight or flight response. And when you intermittent fast, it increases adrenaline, which is a good stressor, because it tells your body to mobilize stored fat to burn the energy, which is a good thing. It also stimulates human growth Hormone, which is really important. It helps with fat loss, and it helps you preserve muscle mass. And this brings me to another common myth about fasting, as you've heard me talk about. I co founded a company called Function Health, which gives you access to over 110 biomarkers for 4.99 membership a year. Now, when you want to see the impact of your fasting regimen on your hormones and biomarkers, you should for sure check out Function Health before and after you do your intermittent fasting regimens. But if you go to functionhealth.com, you can jump the wait list, which is about 300,000 people right now. So, little tip for me. Okay, let's get into the second myth. Myth number two. Fasting causes muscle loss. Your muscle is three times, maybe even more than metabolic, active than fat, and requires a lot of energy to maintain it. Muscle contributes to about 20% of your total daily energy expenditure. For every extra 1 pound of muscle on your body, you burn 6 to 10 extra calories per day. So that's why strength training is so great. It actually makes you burn more while you're just sitting around doing nothing. Now, during prolonged fasting or calorie restriction, the body actually breaks down muscle, which is not good, especially if you're not resistance training or if you're not eating enough protein. Now, this loss of muscle is not a good thing, because then you get a slower metabolism since fewer calories are burned. And that's why I don't regularly do prolonged fasts. When I do this, I'm relatively thin, healthy, fit, don't have insulin resistance. I have to be careful because I will lose significant amounts of weight and muscle if I do too long fast. But I can do 12 to 14, sometimes 16 hours without a problem. When you're fasting, you don't want to lose muscle. You want to build muscle and maintain your muscle, not lose it. Why? Because muscle is the organ of longevity. It's linked to a longer health span and your lifespan. When you have a lot of muscle, it's linked to a longer health span, meaning you're healthy longer and to a longer lifespan. And it does that through a lot of different mechanisms. It lowers the risk of something called sarcopenia, which means less muscle. And that's really this hidden disease of aging that affects so many people. Basically, turning your muscle from a filet mignon in your 30s to a wagyu ribeye in your 60s or 70s, that's bad news. Even if you don't gain weight, you can lose muscle Stay the same weight and you become basically skinny fat. Also, when you look at people who don't build muscle and strength training, they get osteoporosis and you can get chronic diseases like obesity, Alzheimer's, type 2 diabetes. Now, when you have enough muscle, it helps protect against chronic disease by improving your metabolic health. It improves insulin sensitivity. And muscle acts like a sponge. It soaks up sugar and excess fuel from your bloodstream. Now, having muscle also benefits your brain, which is kind of your biggest muscle, not actually a muscle, but it's the thing that you use to run your life basically. And if it's not working well, it's a problem. And so having healthy muscle also leads to improved cognition, to mood, to mental health, and lots more. And that's why we got to combine resistance training with any time restricted eating or intermittent fasting regimen to preserve muscle and get the maximum benefits. When you just do it without the strength training, I don't think it's a good idea. Body composition is really important. And this is really how much fat and how much muscle do you have? Right. Very simple thing, but it's often not looked at. It's one of the most important diagnostic tests we can do. Now, when intermittent fasting is combined with resistance training, meaning strength training, your lean muscle mass is also preserved, which is a good thing. Now some studies suggest that resistance training, while intermittent fasting, improves body composition by increasing muscle mass and decreasing body fat. That's a good thing. And, and so this is really where we want to go. We don't want to fast and lose muscle because that's a bad thing. Now there's a randomized control trial of 41 overweight obese adults. They found that combining intermittent fasting with calorie restriction and regular protein intake, about 25 to 50 grams per meal over eight weeks led to greater reductions in total body fat, in visceral fat, in other words, the inflammatory belly fat and total body weight compared to just calorie restriction alone. So the message here is if you're going to do calorie restriction or time restricted eating or intermittent fasting, strength training is non negotiable. Intermittent fasting in the study combined with time protein intake and calorie restriction positively shifted the gut microbiome to bacteria that help burn fat and improve your metabolic health. More than just calorie restriction alone. Yep. Your gut bacteria actually affect your weight. It's quite remarkable. But you gotta make sure you're getting a protein that's really key. And the ideal amount if you're Active is about a gram per pound of ideal body weight. So if you're 120 pounds, it's about 120 grams a day. Can be 0.7 to 1, but somewhere in that range. And this really helps you fight muscle loss that happens during prolonged fasts. Now here's a tip. Break your fast with a meal that contains protein to halt the muscle protein breakdown from your overnight fast. And then you stimulate muscle protein synthesis. So this is really important, I want you to hear this. When you fast, even if it's just overnight, right from 12 hours, from, let's say 8 at night till 8 in the morning, you gotta start your first meal with protein. If you do what we do in America, which is eat sugar for breakfast, cereal, muffins, bagels, croissants, sweetened sugars, sweetened teas, sweetened coffees, I mean everything that we typically eat in America, it's going to kill you, I promise you faster than if you eat protein. Protein will help you live longer, be healthier. And the key thing is when you break your fast and you eat protein, you it turns on your body's capacity to stimulate the growth and the building up of new muscle. Not if you have sugar for breakfast. Fasting only becomes a problem for muscle mass if you're not substituting calories and carbs with protein and also adding resistance training. Okay, what's the third myth around fasting? Fasting increases the risk of heart disease. Well, there's been a lot of buzz around articles attempting to debunk the benefits of fasting, some even linking it to an increased risk of heart disease, which doesn't sound so. Now one study in particular caused confusion by suggesting that time restricted eating, specifically an eight hour window, which is a 16 hour fast, right. Was linked to a 91% higher risk of cardiovascular death according to the American Heart Association. So that sounds terrible. Now for those with existing heart disease, the study claimed that eating in a window of 8 to 10 hours per day was associated with a 66% higher risk of death from a heart attack or stroke. But let's kind of wait there for a minute and break this down. Let's look at the limitations of the study which were quite significant. First, the data came from about 20,000 US participants from what we call the NHANES study, the national government study, the National Health and Nutrition Examination Survey. Dietary information was based on two self reported questionnaires and relied on participants memory, which is not really good. The data on dietary food frequency questionnaires shows that there are pretty unreliable and there's a lot of bias, right? People often misremember what they ate. They underestimate what they ate, they overestimate the good stuff, they underestimate the bad stuff. Let's face it, we're all human and we don't like to tell the truth. So it's really not an accurate way to evaluate someone's diet. And there's just a lot of data on this and I've written a lot about this, but it's something we need to really be aware of. These food frequency questionnaires can be helpful for looking at maybe patterns or associations, but they don't prove anything. Second, the study didn't account for what we call confounding factors that have influenced participants health or the decision to engage in time restricted eating. In other words, maybe the people who tried to do this were already really sick and so that's why they did it, to improve their health, but they were already really sick and already had a high risk of heart attacks. And maybe it wasn't the time restricted eating at all. The other thing was that overall diet quality wasn't really paid attention to. So I mean, for example, some of the participants might do their fast, but then when they eat, they just eat the standard American diet or have fast food or french fries or sugar or crap. Right? So is it fasting that caused the problem or is it the rest of their diet? And third, the researchers focused only on meal timing and cause of death. They didn't provide other health data, such as things about your critical health factors that determine your risk, like how many calories are consumed during the feeding window. What was the quality of the calories? Was it whole foods or was it the standard American ultra processed diet, which is what we mostly eat in America? 60% of our diet is ultra processed food. Of course, lifestyle factors that they didn't account for, stress, smoking, alcohol, maybe the time of day they're eating is also important. Fasting during the day and binging at night is more problematic than eating during the day and fasting at night. In other words, what if you didn't eat all day and then you had a giant meal at dinner and then kept eating till you go to bed. That's going to have a very different effect on your metabolism. So this is the premise of time restricted to eating or eating within your circadian rhythm. While the headlines might sound scary, it's important to understand, like any study, what the limitations are before you come to any conclusions. So is fasting dangerous for some people? Yes, True. Who are those people? Well, if you're pregnant, not a good idea. If you're breastfeeding, if you're trying to get pregnant, if you have thyroid issues, if you're a type 1 diabetic or you're underweight or malnourished, all those things. Or you're frail or you're elderly or chronically ill, maybe not such a good idea. Now fasting can trigger hormonal changes that cause your body to be stressed, not something you want while you're pregnant or trying to get pregnant. Women who are trying to get pregnant with pcos, which is polycystic ovarian syndrome, or reproductive issues could benefit from time restricted eating or at least eating within a 12 hour window. I think that's just basic like the standard should be. Everybody should take a 12 hour break from eating every day, right? Finish dinner at 8, don't eat till 8 in the morning, finish at 7. Eat breakfast at 7 in the morning. That's not so hard. That's why we call it breakfast break fast, because we should be breaking the fast, not just eating until we go to bed and then eating first thing in the morning.

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Or later required now for most fasting can be safely practiced by many, many people with the right guidance. So we're going to get into the do's and don'ts of intermittent fasting in a bit. But now that we've debunked many of the myths around fasting, let's discuss the benefits. First, it helps your immune system. Fasting enhances immune function and rejuvenates your immune system. It Reduces inflammation, which is a good thing. And it promotes the regeneration of your immune cells, Creating a more robust and balanced immune response. It also helps the body better respond to infections. It also turns on autophagy. What's autophagy? It means self eating or self cannibalism. Essentially, it's the recycling system you have. It's when your body breaks down and recycles damaged dysfunctional cells, proteins, organelles, and cleans up cellular debris. It also helps maintain cellular health by removing waste and promoting repair. So taking this break, why do intermittent fast? Because it turns on these longevity switches. This recycling repair system you have in your body that needs you to take a break from eating all the time, it plays a crucial role also in preventing disease. And it supports longevity by triggering these genetic pathways that are embedded from yeast to humans, which I like to call longevity switches. What are sirtuins? Well, they're a family of signaling proteins that play a central role in lots of really important things your body has to do to stay alive and stay healthy. It helps regulate gene transcription, DNA repair. It shuts down inflammation and free radicals, and it boosts your metabolism. They're also key to maintaining the health of of our mitochondria. These are the energy factories in our cells. They're super essential for repairing damaged DNA and protecting your telomeres, which are the caps on the ends of your chromosomes that are also important for preventing cellular aging. They also play a key role in insulin sensitivity and regulating blood sugar. So that's also good. And sirtuins initiate these effects during low nutrient states like fasting. So when your calories are low, the sirtuins turn on and do all these wonderful beneficial things. But what messes up sirtuin activity? Well, eating all the time, like most Americans, or eating large amounts of carbs and sugar and flour, which is what most Americans do, about 152 pounds of sugar and 133 pounds of flour per person per year in America. And then, of course, as we age, the activity of sirtuins also goes down. So there's a lot of natural things that happen as we get older, but we can actually do things to stimulate sirtuins. Now, boosting sirtuin activity is a crucial strategy for a long, healthy life. So what actually can boost sirtuins? Well, the body activates sirtuins by producing something called nicotinamide adenine dinucleotide, otherwise known as nad. You might have heard of that. NAD is a longevity compound. It plays a key role in reducing inflammation. It helps activate DNA repair. Your body Sends out a whole slew of DNA repair enzymes to deal with all the damaged DNA. That happens every day. As just part of life, it also is critical in energy production. And it increases an incredible compound in your brain called bdnf, which promotes neuroplasticity. It's like miracle growth for your brain. And that's why NAD is so important for longevity. Helps combat all the effects of inflammation. Now, NAD also declines as we age, which then limits the stimulation of sirtuins and their ability to support support these critical functions. So let's talk about what activates nad. Well, calorie restriction, fasting, intermittent fasting, time restricted eating, all those things help. Niacin, which is a B vitamin, it's a precursor for nid. Lots of plant chemicals do this. Polyphenols like resveratrol. You might have heard about sauna, cold plunges, exercise, sleep. A keto diet also helps and that helps reduce insulin levels. It increases fat burning. It mimics fasting. So when you do a keto diet, it has all this benefits, which makes your body thinks you're fasting, but you're actually not. Now you can also do supplements, NAD precursors like NR and NMN that are widely used and, and they can be used to actually increase NAD levels as we age. There's a lot of research on that I talk about in my book Young Forever. So what are the other benefits of fasting? Well, metabolic health. It improves your insulin sensitivity. Fasting improves your body's response to insulin, which is really important because the more sensitive you are to insulin, the healthier you are, the longer you're going to live, the less chronic disease disease you're going to get. Now, if you go for a period of time without eating, your insulin levels stabilize, which helps balance blood sugar and it reduces the risk of type 2 diabetes. But because insulin is low, it also helps burn fat. Because remember I said when you have a high insulin level, it blocks the fat in your fat cells. When it's low, you can start to burn the fat and that allows you to become more metabolically flexible, which is a good thing. You don't want to be metabolically inflexible because that means you can even have a strawberry without getting into trouble. Weight loss is another great benefit of keeping insulin levels low. Since insulin is the fat storage hormone. Fasting significantly also improves clinical metabolic biomarkers. Things we test at Function Health. Now, a randomized controlled trial by Valter Longo and his colleagues showed how the fasting mimicking diet, which is about 800 calories a day for five days reduce risk factors for aging and many age related diseases. Valter Longo's fasting mimicking diet is essentially low in calories for about five days. So it's about five to 800 calories a day. And then you go back to eating normally. You do this once a month for three months. Three months after doing this fasting mimicking diet, there's a whole bunch of beneficial changes that you report, including improved body weight, body mass index, total body fat, belly fat, waist circumference, IGF1, which is a surrogate marker of growth hormone, also improve your blood pressure, systolic and diastolic, non alcoholic fatty liver and cancer. So now improving these cardiometabolic markers helps lower the risk of of all the diseases related to insulin resistance, things like obesity, type 2 diabetes, heart disease, Alzheimer's, cancer, and non alcoholic fatty liver disease, which now is called metabolic associated fatty liver disease or mafld. Now what does the research say on fasting and cancer? Now this is really cool. Dr. Valter Longo's research has been monumental in advancing our understanding of fasting and its potential benefits for cancer prevention and treatment. Now, Valter Longo developed fasting mimicking diet, which is designed to produce similar metabolic effects to long term fasting while allowing you to eat some food, right, so you don't starve yourself completely. But his research suggests that fasting mimicking diets can enhance chemotherapy effectiveness, which is amazing. They can reduce the side effects of cancer treatments like nausea and fatigue. They protect normal cells from chemotherapy damage while making the cancer cells more vulnerable. Now, Dr. Langer's research has shown promising results, but it's important to note that fasting as a cancer intervention is still an active area of research. People should always work with their healthcare team before considering any fasting regimen, especially in the context of getting cancer treatment. All right, what else? Cancer. We talked about metabolic health. What about brain health? Fasting also has amazing effects on the brain. It increases what we call BDNF or brain derived neurotrophic factor. And what that does, it increases the connectivity between your brain cells called neuroplasticity, and also increases something called neurogenesis, which is making new brain cells, specifically in the hippocampus, which is the area of the brain that enhances memory, learning and overall cognitive function. And longer fasts boost ketone production, which is basically clean fuel for the brain. Now, intermittent fasting reduces inflammation in the brain. It increases the clearance of something called amyloid beta, which is important. And that does so by inducing autophagy and amyloid beta is what's increased in Alzheimer's. Mouse studies have shown that time restricted eating improves memory and cognitive function. Now, some clinical studies have even shown the benefits of intermittent fasting for conditions like epilepsy or Alzheimer's or multiple sclerosis in terms of disease symptoms and progression. Now, these findings still need more research, but it's kind of interesting data. Now, intermittent fasting can also help reset the body's internal clock. So what does that mean? Well, this is your circadian rhythm. When you fast, it's really important to fast with your circadian rhythm, not against it. So what do I mean by that? Well, human beings are biologically programmed to digest and absorb food best earlier in the day. This is known as circadian eating. Dr. Satchin Panda is a lead scientist in circadian rhythm research. That means doing daytime things when the sun comes up, like eating, moving and working and nighttime things when the sun goes down, like winding down and sleeping. Duh. Right. Dr. Panda discovered that thousands of genes turn on and off at specific times of the day, which affects people lots of different bodily functions. Your circadian rhythm affects your body's ability to digest your food. Now, insulin sensitivity, which is really important, is highest in the morning and it decreases during the day. Our digestive system produces less saliva, stomach acid and digestive enzymes at night, which is why late night eating is a bad idea. And yet it's what we do mostly in America. What happens when you eat late? Well, it causes blood sugar swings throughout the night, makes weight loss harder. It messes up your REM sleep, which is your dream sleep, and increase the risk of type 2 diabetes. It also puts energy towards digestion. It takes energy away from rest and repair. At night, your body's supposed to rest and repair and heal, but when it's digesting, it can't do that. And time restricted eating might also help extend your lifespan. A study on firefighters showed that 1410 time restricted eating, meaning 14 hour fast, 10 hour eating windows for six weeks, improved octave stress and reduced something called advanced glycation end products, which is a marker of aging, inflammation and cardiovascular disease. Now, eating an earlier dinner or fasting for at least three hours before bed can improve sleep. It can support weight loss, it can improve your immune function and your metabolic flexibility and prevent chronic disease. So lots of benefits. So are the benefits of fasting due to not eating, to calorie restriction or eating within your circadian rhythm? Well, it's probably a combo effect. Now let's talk about what you have to do and how to do this properly. What's a step by step guide to properly fasting? Many people ask me how to fast successfully. Here's what I tell them. Be intentional about it Select a specific day to start your fasting journey. Fasting without a plan can lead to food emergencies, hunger and the temptation to break your fast early with bad food choices like carbs and sugar. Now, being intentional about your fasts helps mentally prepare you and it also allows for proper planning. So choose a day that aligns with your schedule so you're not faced with social pressures or eating challenges. Pre plan your meals to ensure they are nutrient dense and incorporate good quality proteins, healthy fats and lots of veggies to keep you satisfied until the next meal. Now I just want to make a special comment here about women in their reproductive years and fasting now having time restricted. Eating 12 to 14 hours a day of fasting is generally safe. As I mentioned earlier, it can even actually be beneficial for women with pcos, which is driven by insulin resistance. And I generally recommend that women fast during what we call the follicular phase, which is the first half of their cycle, when the estrogen levels are rising and the body is better equipped to handle stress. And women can fast during the luteal phase, that's the second half. But they should do so mindfully, maybe 12 hour fasts instead of 16. And I think extended fasting can be problematic for women in general. Now chronic undereating can signal a stress response to your body that increases cortisol, messes up your hormones and promotes fat storage. So don't do that. Here's the second step. Start slowly with just doing a 12 hour fast and 12 hour eating window. That should be minimum for everybody. It's just foundational to health. So that's easy to do. Most people aren't doing it, you shouldn't do it. It's easy to do, but it's something you should start with. So just begin with a simple fasting regimen like 12 hours on, 12 hours off where you fast for 12 hours and eat during the remaining 12 hours. That's doable for anybody. It should be the basic foundational for health. Start there and then just work your way up. Maybe go to 13 hours a fast and then 14 hours and maybe 15 and 16. See how you feel. Just pay attention to your body. It's the smartest doctor in the room. That's going to also help you minimize any discomfort and making it all more manageable. Next step is be consistent regular fasting Rather than sporadic, long fasts can be more beneficial and sustainable. I don't really want to call it fasting because it's more like just time restricted eating. And for many individuals, just 12 to 16 hours of fasting are enough to reach and also maintain their health goals. So you don't have to go on 2, 3, 4 day, 5 day fasts. The problem with those is you end up losing muscle. It can be problematic now for some patients. It can be helpful in certain conditions. I'm not against it, but it should be done under medical supervision. You also want to eat at the same time every day. Eat most of your calories during the day, not at night. Also, next step, listen to your body. Adjust your fasting practice based on how you feel. Are you tired? Maybe you're dehydrated? Drink a glass of water. Electrolytes feeling tired and lethargic may be normal to some extent. When you start to do these time restricted eating periods, are you feeling weak or dizzy? Your eating window might be too short, Maybe widen it an hour or two to see how you feel. Plan a nutritious breakfast. You know, how you break your fast is really, really, really, really important. And it will impact your health and your fasting experience. So you want a breakfast that's nourishing, that is good, and you want to start with protein. Now an omelette's a great way. You can put lots of veggies in there. You can have whole fat, grass fed, maybe sheep or goat yogurt. I like that better than cow yogurt unless it's a two casein and regeneratively raised. But you can have that with some nuts and berries. A smoothie is my favorite. I use protein powder, usually goat whey. You can throw in some greens like spinach, flaxseeds. Have a turkey patty with avocado, lime, aioli. Lots of different ideas, but protein and fat for breakfast, not sugar and starch. Okay, next step is eat nutrient dense foods. Right? Fasting doesn't have to include calorie restriction. The primary focus should be on the timing of eating rather than the amount of food. Don't worry about amount you're eating because when you focus on the quality of the food and the timing, your body will naturally take care of things. To ensure the adequate intake of essential nutrients. I want you to prioritize consuming whole nutrient dense foods during those eating windows. And this includes a balance of protein, healthy fats and non starchy veggies, which are by the way, carbohydrates. You can have Some whole grains you can have some beans, nuts and seeds. Also carbohydrates. Basically plant foods are carbohydrates, but they don't have to be flour and sugar. Next step is stay hydrated. Really important because when you start to restrict calories, you drop your insulin levels and you start to pee out a lot of salt and water and you can become dehydrated so you want hydration. It's really important for maintaining your energy. It helps digestion, supports your metabolic function. I always start my day by drinking at least 4 cups of water with electrolytes and aim to drink half my weight in ounces every day. Now you can also use herbal teas, black coffee during fasting periods, but don't add sugar creamers. Next step, gradually extend the fasting period. As you become more comfortable with fasting, maybe consider extending it a little bit and maybe try going from 1212 to a 168 or slowly transitioning where you fast 16 hours and eat in the 8 hour window. You can also make gradual adjustments based on how your body responds and just listen to your body. So make gradual adjustments based on how your body feels, how your body responds, and that way you're going to ensure its practice can become a sustainable part of your lifestyle and health routine. So as we've explored today, fasting doesn't have to be a metabolism slowing monster. It's often made out to be when approached correctly, especially with short term fasting methods like intermittent fasting, time restricted eating, it can actually boost your metabolism, it can help you burn more fat and it can improve your overall health. It's all about finding the right balance for your body and your lifestyle. So whether you're looking to improve your metabolic health, manage your weight, or simply give your body a reset, fasting can be a powerful tool when used wisely. The key takeaway don't fall for the myths and understand the science behind fasting. Listen to your body. Your body is the smartest doctor in the room. I always say that don't listen to doctors, don't listen to the science. See how you feel and how you respond and then learn from what your body's telling you. Also remember, fasting is just one piece of a puzzle combining with a nutrient dense diet with regular exercise, but stress management, it's going to give you the best results. So I want to thank you for joining me today. And don't forget to rate, review and follow health hacks wherever you get your podcasts. Stay healthy, stay informed and I'll catch you next Tuesday for another episode of Health Hacks.