– From the start, I wanted this video to be more than just a rundown of how to do a water fast and lose fat. While I do include a walkthrough, I also wanted to take a deeper look at the additional benefits to health and wellness that people report, and really dive in on the scientific research which backs everything up. As well as check for evidence behind some of the common criticisms of water fasting. In this video, we cover everything you need to know to maximize your results. From what to expect during a water fast, and what’s all right to consume during one besides just water, as well as common questions, like how much fat will I lose per day? What will happen to my muscles? And will water fasting lower my metabolism? Rule number one, though, is to know your enemy.
So the first question we should be asking is, what even is fat? Body fat is comprised mostly of fat cells. Known scientifically as adipocytes, these cells are comprised of a lipid droplet surrounded by a thin membrane. The lipid droplet can grow and shrink as needed, allowing the fat cell to expand and contract. The human body contains over 30 million of these cells. Simply put, the goal of any fat loss method is to reduce the size of these millions of little drops in the millions of fat cells across your body.
As I’m sure you know, these cells don’t just exist to afford our fashion choices, they provide a way to store excess energy long term. This way, if we eat more food than we need, the excess energy can be stored for release during conditions in the future when we are eating below what we need. One of the first mentions of dieting was in the year 1087 when William the Conqueror, having become too fat to ride his horse, decided he would stop eating solid foods and undertake a liquid-only diet. This would mark the beginning of humans categorizing what they consume based on certain qualities and using those labels to adjust their intake and lose weight. In 1863, William Banting expanded on the idea, but with added precision. He figured out you don’t actually need to cut out all solid foods.
He noticed that specific foods, such as sugar, starch, beer, milk, and butter seemed to play a disproportionately high role in fat gain, which led him to publish one of the earliest fat loss guides. So we’ve gone from dividing foods based on solid and liquid to now a more complex system. “But wouldn’t it be better “if we could take the precision even further?,” people thought. Researchers began developing a system to compare all foods. In 1918, Lulu Hunt Peters’ book, “Diet & Health: With Key to the Calories,” seemed to have cracked the code. The book encouraged dieters to consider all foods, not in terms of healthy versus unhealthy labels, but rather their individual energy content. And Lulu had figured out how to do it. The energy in food comes in the form of three distinct macronutrients. Protein, which are chains of amino acids.
Fats, in the form of triglycerides and free fatty acids. And carbohydrates, which take the form of simple and complex sugars. These three macronutrients are very different. The body processes them differently, stores them differently, and even burns them in a specific order. Despite this, Lulu’s book seemed to have the answer. Figuring out how much heat energy a gram of each would release when burned so that way everything we eat could be compared on an equal playing field. The Calories In, Calories Out diet became hugely popular in the fitness space. The idea being if you could calculate how much energy you’re burning in a day, then all you need to do is set your daily intake below your burn, and voila, this will force your body to tap into the calories locked up in long-term fat storage to fill this energy deficit. As you watch further, though, you’ll quickly realize by only looking at how much energy is released when macronutrients are burned, and ignoring that they are burned and stored in different orders, can cause you to miss the bigger picture.
Like a daily Calories In, Calories Out diet, water fasting also involves creating an energy deficit, but on a larger time scale. So while someone doing Calories In, Calories Out may set their daily intake 500 calories below their estimated burn, leaving them with a deficit of 500 calories each day, someone doing water fasting is looking at the bigger picture. They will spend anywhere between one and several days consuming zero calories. No food, no drinks, just water. Well, with a couple of exceptions, but I’ll hit on those later. So off the bat, one advantage of water fasting becomes clear, and that’s the speed. For example, assuming a consistent daily burn of 2500 calories, in just 72 hours, you’ll have burnt 7500 calories. This same level of weight loss would have taken the person on the cutting diet 15 days.
This speed advantage has been confirmed by research studies. In one review, researchers remarked on the significant amounts lost over short durations. For example, in one study, men fasted on and off for two weeks, and by the end, had lost three percent of their body weight. In another study, women lost four percent of their body weight after three weeks of on-and-off fasting. Another advantage to water fasting is, after the fast is complete, the person fasting doesn’t need to continue to eat below their daily burn.
Remember, they’re looking at the big picture. As long as they’re in, say a weekly calorie deficit, there may be days within that week that they eat in a slight surplus, unlike the daily calorie restriction dieters whose bodies remain in a deficit day after day. So while water fasting has the potential for faster fat loss, including occasional daily surpluses, has actually resulted in studies showing more participants stick with these periodic fasting diets. And, as a result, they’re able to lose more weight because they don’t quit. So there’s a benefit in speed and a benefit in participants sticking to it longer. But, what else? While there are still so many benefits to cover, I know many of you may also be curious for a practical guide on how to approach a water fast. So next, I’ll walk you through a typical water fast, but I’ll use the research to talk about what’s happening metabolically and hormonally throughout it.
This way, we get a good idea of the additional benefits. You might be thinking, “What preparation?” All you need to do is stop eating. While water fasting is for sure simple, there’s still a few things to keep in mind. Before starting, I think it’s always a good idea to first decide how long you intend to water fast for. Studies consistently show you’re more likely to achieve a goal if it’s clearly defined. If you go into it without a committed length in mind, it’s easier to justify ending it earlier than you might have wanted to.
– So how long are you going to water fast for? (whimsical music) – Oh, you know, I was thinking of going for nine hours, 27 minutes, and 54 seconds. Oh, would you look at that? (whooshing) The choice of duration is actually quite broad. While some people will just water fast for 12 or 16 hour portions of each day, there are some water fasters who go up to 30 days straight, or even a bit longer on the extreme end. I’ve noticed a lot of people in fasting groups on Facebook who will jump in and seem to pick the most extreme length right off the bat.
While I’m not gonna tell you what to do with your body, you should realize that starting small and building up is a time-tested approach to achieving a big goal. So personally I do a 60 or 72 hour water fast each week when I have fat to lose. I’m perfectly content with losing two to three pounds per week. On the remaining days, I just keep my eating within an eight-hour window, for reasons I’ll explain later. People do definitely take it longer than my 72 hours, though. And while safety studies show water fasting is generally well-tolerated for durations up to 21 days, it is crucial to remember that the people in these studies have first been given a medical exam to check for nutrient deficiencies before being cleared to participate.
If one of them was deficient in nutrients or had an underlying medical condition, it could have been a different story. This is why I highly recommend you talk to your doctor and get your blood levels checked. Run your fasting plan by them and they can help you address any vitamin or electrolyte deficiencies before it becomes a problem. This is especially important if you are diabetic or on medication. Dr. Jason Fong recommends that, if you’re on medication or diabetic, you consult your doctor if you plan to fast beyond 24 hours. Another recommends anyone going beyond 16 hours should be monitored. Leading up to your water fast, it is a good idea to stay well hydrated. Also including adequate fiber in your diet beforehand is recommended to help prevent constipation. Let’s now walk through a five-day water fast. This is a bit longer than the ones I do, but will ensure we can cover all the hormonal and metabolic shifts.
In 1976, Dr. George Carhill published research which outlined some distinct metabolic phases humans go through following their last meal and through the duration of a fast, which will help explain what’s going on. Since a water fast is an extended period without consumption of food or drink, your fast begins the moment you consume your last meal and begin absorbing those final calories. Notice though, I use calories as a way to describe your last meal. After all, calories measure energy, right? The problem is this way of looking at it implies that energy content in food is all that matters. As we go through the fasting cycles, though, you’ll quickly see your body actually treats carbs, fats, and proteins very differently. While, for the purpose of this example, we are going to assume your last meal contained all three macronutrients, I think after watching this you’ll understand why usually my last meal before a fast consists mainly of proteins and fats and why calories don’t tell the whole story. So we start with digestion. We’re all familiar with the digestive system. Consume a meal and various digestive enzymes break the food into its basic elements.
Dietary fats, which usually take the form of triglycerides, are emulsified into smaller droplets, allowing enzymes like pancreatic lipase to go to work on them, splitting them into their individual free fatty acids, which can then enter the bloodstream via lacteals, where they can either fuel cells throughout the body or be absorbed into fat cells for storage. Carbohydrates, too, are often consumed in more complex forms than what can be absorbed into circulation. These complex polysaccharides, which are chains of unique sugars, also need to be broken down by digestive enzymes into their simpler monosaccharide forms before they can be absorbed. Glucose is the body’s preferred monosaccharide and can be used immediately after absorption. Other monosaccharides, like fructose, must first travel to the liver to be converted into glucose. Amino acids from proteins ingested are primarily used to create new cells but can also be used to synthesize glucose, through the process of gluconeogenesis, to yield four calories per gram. Glucose, despite also having just four calories per gram, has some big advantages over the other two.
Firstly, it is much faster for cells to convert a glucose molecule into energy, and nearly every cell in the body can run on glucose, so glucose is less energy dense but releases energy much faster. Fats, on the other hand, contain nine calories per gram. This means a gram of fat can be used by a cell to create more energy, making it a more dense and space-efficient molecule. The drawback, though, is tapping into it is a slower and more complex process, and some cells can’t run on it, namely a few parts of the brain.
Over centuries of evolution, our bodies taking into account the pros and cons of these different macronutrients, have developed a response which ensures everything is used in the most efficient way. To achieve this, it uses the hormone, insulin, a hugely important hormone when talking about any fat loss method, especially water fasting. When levels of nutrients in the blood increase after a meal, the pancreas detects this and releases bursts of insulin, causing blood levels of insulin to rise. While the high blood glucose levels that come with digestion of carbs are one of the most potent triggers of insulin release, various amino acids found in proteins can also trigger it. With one study noting that while blood glucose and insulin scores were highly correlated, protein-rich foods and bakery products, which are rich in fat and refined carbohydrates, elicited insulin responses that were disproportionately higher than their effect on blood sugar.
– Hold on, all these insulin-raising foods remind me of the same foods Banting said to avoid to lose fat all the way back in the 1800s. Does this mean high insulin works against fat loss? – Basically, yeah, but there’s a good reason it does. Insulin’s job is to coordinate the body’s response to a sudden delivery of macronutrients into the blood. It travels through the body and binds with insulin receptors on all sorts of different cells making sure every nutrient is either brought into a cell that needs it or stored for later. Because the glucose it gets from carbs delivers energy rapidly and with the least amount of oxygen required, the body prioritizes burning that first.
Insulin binds with cell receptors, letting them bring glucose in right away. Most cells are able to store a small supply of glucose within themselves to be used for instant energy. Many of these cells, including muscle cells, rely directly on insulin to be able to absorb this glucose. You might be wondering, fats contain nine calories per gram, wouldn’t it make more sense to burn those first? Well, no, because besides releasing energy more slowly and requiring more oxygen to burn, remember, our bodies survive by being as efficient as possible. Because fats pack more potential energy into a smaller form factor, the more efficient thing for the body to do, if there is still glucose around, is to use that first and store the fat, because it takes up less space.
So while insulin is triggering cells to take up glucose, the acetyl-CoA carboxylase enzyme in the liver is producing something called malonyl-CoA, which blocks cells in muscles and many other organs from burning fat at this time. So despite taking in calories from carbs and fat, it’s just the carbs being burned right now. Fat is being stored. Once cells have taken in all they can, any remaining glucose in the blood will need to be stored as well. Your body actually possesses a short-term way of storing energy from carbohydrates, which it fills first.
This is super relevant to fat loss but often not talked about. It stores the glucose as something called glycogen. Glycogen is simply a more complex and stable sugar which acts as a short-term storage option. Insulin activates the liver enzyme, hexokinase, which instructs liver cells to trap passing glucose within them. It then activates enzymes which synthesize glycogen out of this glucose. The liver has a capacity of about a hundred grams of glycogen. Additionally, another 500 grams or so of glycogen can be stored in the muscles. All in all, this glycogen can represent up to 2,000 calories of stored sugar. Since this glycogen is stored along with water, being fully carbed up will make your muscles look a bit bigger and you’ll weigh a bit more, too. Once those first two options are filled, insulin continues to bring the blood glucose down by stimulating the liver to convert glucose into fat for storage. It does this by first turning the glucose into lipoproteins.
These lipoproteins are then ripped apart in circulation into free fatty acids. Since it just packed 24 hours worth of glycogen into short-term storage, and the malonyl-CoA is preventing cells from burning fat, this fat being created in the liver along with the fat from your meal, circulates the blood as lipoproteins. High insulin levels activate pathways which tell the fat cells to begin expanding, absorbing the fats out of the blood and locking them into storage. And, of course, it wouldn’t make sense to fill fat cells up just to empty them out again, so as long as insulin levels are elevated, the breakdown and release of fat from these cells is also prevented. Insulin does this by tying up multiple components in the pathways which release fat from cells.
So, despite both macros containing calories, for the foreseeable future, we’re running mostly on just the carbs and the fat is being securely locked away. What about the proteins during all of that? Remember that amino acids aren’t primarily for energy. They are the building blocks of our body. Amino acids enter what’s called the free amino acid pool. Between meals, a small amount of amino acids in muscle are broken down and enter the pool at a rate of about 75 grams per day. Some of them are used to synthesize key hormones, such as serotonin. The liver can also convert amino acids from the pool into glucose through gluconeogenesis.
Right now, though, the elevated insulin levels are telling the body that that’s not necessary. These new amino acids instead signal growth pathways as they replace the amino acids lost from the pool before the meal. The amino acid, leucine, is a particularly strong trigger of this protein synthesis, triggering the mTOR pathway which stimulates cells to grow, divide, and take full advantage of the opportunity. Interestingly, the more protein you typically eat, the more is broken down into the pool between meals. And on the flip side, engaging in resistance training, in other words, weight lifting, actually reduces the overall amount of breakdown between meals. Now that we’ve covered what happens with all the macros, we can get on with the fast and enter the post absorptive period, which usually starts after about four hours and lasts about 24 hours.
I usually start my water fasts at midnight, so when I wake up the next morning, this is where I am. During this period, falling insulin levels tell the liver blood glucose is getting too low and that it’s time to stop turning glucose into glycogen. The system now operates in reverse and the 2,000 calories of stored glycogen begins getting turned back into glucose and released into circulation to keep powering your brain and muscles. This breakdown of glycogen into glucose keeps insulin levels up, so as long as we have glycogen left, fat also stays locked away in the fat cells. As far as hunger goes, levels have been measured in fasting subjects by examining levels of the hormone ghrelin. Ghrelin is sometimes called the hunger hormone, and studies have shown that over this first day, it will rise during meal times only to fall again after you miss the meal. Now, as the 16 hour mark approaches, glycogen stores are nearing depletion. As this happens, blood glucose and insulin levels fall. Hunger signals reach their highest point here and you may even feel like you have difficulty concentrating.
In my opinion, this 16 to 28 hour period is the hardest part of any fast. Contrary to what many would assume, though, from here everything actually gets better. While our ancestors did it all the time, many people today have never even gone without food beyond this point, so they simply assume it only gets worse from here. That’s not the case, though. See, while you might be feeling frustrated and hungry, your body is implementing an amazing metabolic shift. Since insulin levels have fallen, fat cells are now able to begin releasing free fatty acids back into the bloodstream. It’s during this 16 to 28 hour period that cells like your muscles are shifting over to burning this fat for fuel.
Now a small number of cells, such as red blood cells, will always need glucose, but through a mechanism called gluconeogenesis, the liver and kidneys are able to synthesize a small amount of glucose out of a variety of different substrates. Glycerol stored in fat cells, amino acids in the free pool, lactate, and pyruvate can all be turned into glucose for these few cells. This also begins happening now. Interestingly, in most mammals, this small amount of glucose created in the body would be used to fuel the brain, too. But because our brains are so large and key to our survival, we humans are unique in that our brains actually have a back-up plan.
While no mammals brain can run on free fatty acids directly, in humans, the liver is able to partially oxidize them for energy, releasing special fat-derived byproducts called ketone bodies, which are able to cross the blood-brain barrier and begin powering parts of our brain, too. Something even hibernating bears can’t do. Further proof that this is a situation our bodies are built to expect. Fasting is in our DNA.
Unlike muscle, which shifts quickly to running primarily on fat for energy, as glycogen runs out, the brain’s shift takes a bit longer to reach peak ketosis. By day four, though, research has shown that subjects’ brains are running on as much as 75% ketones. While the shift to running primarily on fat was between 16 and 28 hours in this example, remember, we were assuming a full supply of glycogen going into this. If your last meal didn’t contain many carbs, your glycogen levels would have already been lower, meaning the transition would have happened a bit sooner. This is also why I said that by just looking at the calories of a meal, you’re missing out on some of the bigger picture. Certain foods trigger insulin more intensely and high insulin levels tell the body to prioritize the calories in the carbs over the calories in the fat.
So let’s look back at our graph following a large meal. There’s an order. Dietary carbs are burned right away or stored as glycogen. Fats, although consumed at the same time, aren’t used immediately and kept in reserve. Glycogen is burned and then the remainder is made up of fat and some protein that gets oxidized out of the pool. When carbs are being prioritized, fats are being stored, so the more carbs in a meal, the longer before fat will be burned. This is why water fasters frequently talk about insulin because they know that only in the presence of low insulin will the body be able to burn fat for energy. This graph shows blood insulin levels over a 72 hour fast. You’ll notice while 70% of the insulin drop takes place within the first 24 hours, insulin and its signals to block fat breakdown continue to fall through the rest of the fast.
It now makes sense why eating at a traditional caloric deficit can be so unpleasant. Yes, in theory, insulin should drop enough between meals, allowing fat burn to make up the caloric deficit. But you’re going to be going through that unpleasant transition each and every time and getting blasted with hunger signals all to burn a few calories worth of fat between each meal. Water fasters who go for several days only have to go through that unpleasant metabolic shift one time. After which, fat-burning can continue to ramp up while insulin keeps falling. This is also why I keep my eating within an eight hour window on days I don’t fast to give my body a full 16 hours to get insulin as low as possible and release fat with the least interference. Studies have shown, once in this fasting state, if you eat even just 7.5 grams of glucose, the insulin response will snap you out of burning fat and cells will once again prioritize burning through these new carbs, locking the fat back up.
Kinda explains why water fasters can seem so adamant that it must be water only. Assuming you don’t do this, though, and break it, what kind of fat loss can you expect after this shift? During the first five days of a fast, subjects tend to lose weight far more rapidly than they do later on. One study, for example, saw a subject lose an average of 0.9 kilograms over the first five days of his fast while the days afterwards average about 0.3 kilograms lost per day. So does this mean you’ll lose more fat over the first five days of a fast? Actually, no.
The enhanced initial weight loss is caused not by excess fat being burned but by the body’s switch to burning fat and ketosis itself. The switch causes the body to drop large amounts of sodium. Since sodium is one of the main electrolytes used to hold water in our bodies, the body also begins dropping water, leading to this extra weight loss. This is also why many experts recommend consuming sodium during your fast to replace these accelerated losses. The rapid loss of sodium at the beginning of a fast can even result in symptoms of hyponatremia, including headaches and dizziness. Many, including me, choose to consume between 0.5 and one teaspoon of sodium chloride per day to help offset these losses. I have another video where I dive deeper into this topic. Electrolytes, like sodium, potassium, and magnesium, have no caloric value, don’t spike insulin levels, and play a key role in maintaining proper fluid balance within the body. This is why it’s smart to get your blood levels checked before fasting. And, beyond sodium, many choose to supplement potassium and magnesium as well during water fasts for added insurance against losses.
Sodium chloride is typically supplemented at a rate of about 0.5 to one teaspoon per day during water fasting. One to 1.5 teaspoons of potassium chloride is usually what’s recommended for potassium. For magnesium, though, you’ll want to check the back label. It’s normal for supplements to comprise as little as 15% actual magnesium, so check the back of the bottle and aim to get no more than 350 milligrams of actual magnesium. You can also pick up a pre-dosed electrolyte formula but make sure it’s fasting-friendly. Often these formulas will include glucose, which, as we know, breaks a fast. If I manage to find a good one, I’ll link it in the description below. Back to water weight. Once you finish your fast and consume carbohydrates again, the portion of the weight-loss that was water weight will return. This can actually discourage some people who mistakenly think that all the fat they had lost has just returned.
But, don’t worry. Although water weight will return, you’ll still be down by the fat you lost. How much actual fat you’ll lose will depend on your personal energy expenditure, but as a general rule, you can expect to lose somewhere between a half and a whole pound per day. Putting our subject’s daily loss of 0.3 kilograms, or 0.66 pounds comfortably within that range. So now we’re over 24 hours into our fast. At this stage, water fasters might also begin to notice a mental shift.
Clinicians have noted in subjects increased levels of alertness, mood improvement, a subjective feeling of well-being, and even occasionally euphoria. Over these first few days of fasting, the brain is running increasingly on ketone bodies. The effect of them in humans has been described as indistinguishable intellect-wise, but when investigated for other positive benefits, studies have shown decreases in markers of neuro inflammation and increases in levels of brain-derived neurotrophic factor. BDNF plays important roles in learning and memory with higher levels shown to enhance synaptic plasticity.
While the increases in energy and focus reported by water fasters may stem from increased levels of norepinephrine, a catecholamine, which operates as a hormone and stimulatory neurotransmitter in the body. In normal subjects, levels are usually near zero during sleep and reach their highest levels during the fight-or-flight response. However, during fasting, levels rise rapidly. One study saw subjects’ norepinephrine levels more than double over a four-day fast. Norepinephrine’s ability to increase arousal and alertness explains a lot of the mental effects fasters report, including explaining why some find they sleep less during their fasts. Doctors and researchers also use these elevated levels to explain why studies often show, that when water fasting, a subject’s resting energy expenditure often remains constant or even increases. In the same study which saw the increase in norepinephrine levels, a subject’s resting energy expenditure actually increased over the course of their fast.
The researchers acknowledge, though, that had the subjects continued fasting for longer, their resting energy expenditure would most likely have dropped, which has been shown in longer term fasting studies. Another reason I keep mine to 72 hours. From a survival standpoint, it makes a lot of sense. Imagine if our caveman ancestors didn’t find food for 24 hours, then suddenly their metabolism slowed down and they started feeling lethargic and wanting to sleep, they would never find food. The release of norepinephrine kicks them into hunter mode, trading a small increase in energy expenditure for the benefits of increased vigilance, reaction time, and memory formation and retrieval, all to give you the best possible shot at finding food. This norepinephrine boost is, in my opinion, more potent than any pre-workout formula. The level of intensity I feel in the gym during a fast are amazing. Studies have even shown increases in VO2 max. Evolutionarily it makes sense that it’s gonna be when survival is on the line that your body allows you to unlock the highest possible state of performance.
And while all this happens, the hunger hormone, ghrelin, continues to drop. If we look at this one study, while it still spikes around meal time, each subsequent spike is smaller and smaller. But speaking of meal times, there are a few other things that some people choose to consume during their fasts. A lot of this comes down to personal preference. Still and sparkling water are always okay to consume during a fast and most people accept that electrolytes are a good idea also. Despite some people talking about dry fasting, fasting without water, I would never recommend it. There simply isn’t enough research. In fact, I’ve seen a prominent YouTuber, who I won’t name, make a video about dry fasting, but only linked to non peer-reviewed articles. Then there are zero calorie drinks like black coffee, in other words, coffee with no cream, milk, or sugar added, and unsweetened herbal teas. These are a bit more of a gray zone because they contain as near as makes no difference zero calories they won’t bring you out of your fasted state.
So does that make it okay? As far as insulin goes, I’ve yet to see a study that shows black coffee or unsweetened herbal tea could cause insulin to rise. In fact, one analysis linked coffee consumption to lower levels of fasting insulin. So hot drinks like black coffee, green tea, black tea, herbal tea, those won’t take you out of your fasted state. The research is less conclusive on artificial sweeteners, though. Not only has research shown that they can actually boost hunger and cravings for sweet food, a study on sucralose demonstrated an 8% increase in insulin levels versus consuming plain water. Personally, I avoid them all the time and many fasting experts recommend avoiding them during your fasts.
Despite that, though, the impact on actual fat loss of consuming one during your fast would be minuscule. Some people also choose to consume bone broth during their fasts. Bone broth is essentially a stock prepared by simmering bones, usually beef bones, for several hours to release nutrients into the water. As a result, it will have a small but significant fat and protein content. While a couple of grams of protein or fat might not kick you out of the fasted state, it could certainly have an impact on some of the other health effects of fasting, such as autophagy. I personally save it for when I’m breaking my fast. The last element of the fast before we break it and finish by hitting on some additional health benefits and criticisms is what happens with muscle. Back when we were digesting, I mentioned that studies have shown that, in a day, a typical person loses and replaces about 75 grams of protein.
In the fasted state, though, this amount falls dramatically to between just 12 and 20 grams per day. If you resistance train your muscles, you’ll upregulate protective pathways in the muscles you train, reducing breakdown further as confirmed by studies. I’ve also done an entire video, which I’ve linked to, which explains some of the other hormonal processes which activate during fasting to protect muscle, including a massive uptick in the release of human growth hormone. This should give you another reason why, as someone who cares about their performance in the gym, I don’t typically fast beyond 72 hours as a way to keep the protein losses easily replaceable. When it comes to breaking a fast, the best advice is to take it slow. In fact, this is where I will usually use bone broth as a gentle way to re-engage digestion. Okay, so now that we’ve covered nearly all the basics, you have most likely heard that fasting brings with it some deeper health effects, with some researchers investigating whether it can fight many degenerative diseases and increase lifespan.
While fasting activates several pathways which could, in theory, have an effect on this, the one you’ll hear the most about is called autophagy. I plan to make a full video on it and the other longevity pathways in the future but enough people talk about it that it’s worth a brief explanation here. Have you ever considered that some of the longest-lived animals often grow slowly and go long periods without eating? Increasingly, research is showing that cells within our bodies are similar. Constant nutrient availability turns on growth pathways, like mTOR, pushing cells to rapidly grow and divide. When you fast, though, mTOR is suppressed, slowing down the cellular division.
So if cells aren’t dividing, what are they doing instead? Well, within any given cell are specific structures which perform key tasks. I bet you’ve even heard of some of them, like the mitochondria, which generates ATP energy, or the lysosome, which breaks down nutrients a bit like a stomach. As cells age, these organelles become less efficient. Sometimes proteins misfold during replication, resulting in the accumulation of cellular clutter. The constant generation of energy can produce toxic byproducts, such as free radicals, which further damage the cell and even its telomeres. These types of cellular breakdown have been implicated by researchers in the pathology of a whole host of degenerative diseases. As it turns out, though, cells actually possess a way to gather up the damaged components within themselves, break them down, and recycle them.
A recently discovered organelle, called the autophagosome, forms to surround these damaged elements of the cell. It then traps them and brings them to the lysosome, that stomach organelle, for recycling. The raw amino acids can then be used to synthesize new healthy organelles or even entire cells. I suppose you could even say reversing some of the effects of age on a cellular scale. Now it makes sense why autophagy comes from the Latin root, self-eating. But what does this have to do with fasting? Well, as it turns out, during the post-meal state, autophagy is significantly reduced. This makes sense considering the amino acid, leucine, is a powerful trigger of the mTOR growth pathways as we mentioned.
As long as these growth pathways are active, our cells prioritize processing these dietary nutrients and multiplying over self-cleaning and autophagy. However, when you fast, leucine levels drop, mTOR powers down, and another pathway, known as AMPK, begins powering on. AMPK is sometimes known as the longevity pathway and its activation reduces growth in favor of making sure the cells you already have run as efficiently as possible. Instead of a focus on division, the focus turns to producing autophagosomes, which recycle damaged and waste proteins. Studies in mice have looked at the quantity of autophagosomes over a fast. After 24 hours, autophagosome count per liver cell more than doubled with a similar effect in mouse brain cells as well. After 48 hours, the number further increased to over 300% above baseline. Considering that our ancestors were constantly facing periods of fasting, it makes you wonder whether our bodies evolved to rely on these periodic fasts as their signal to recycle and repair. I can just imagine my cells before I started fasting, patiently waiting for the signal to kick up autophagy as more and more cellular waste built up.
Beyond autophagy, there’s even more exciting health research. Scientists at MIT, for example, noted a fasting-induced increase in stem cell production in the intestines, which significantly improved their ability to regenerate. I’ll cover autophagy and these other pathways further in an upcoming video. Hearing all of this, though, it makes more sense when you read studies like this one, which found mice which were put on an every other day fasting diet lived 30% longer. Before we end this video, I want to address one of the most common criticisms of fasting that you’ll hear, which is that you’ll slow down your metabolism. Well, we’ve already seen that that’s not true during shorter water fasts, and in a study of a four day fast, resting energy expenditure actually increased, the same can’t be said for traditional calorie restriction diets.
In fact, research on these consistently show subjects that set a deficit will lose weight for awhile, but slowly their total energy expenditure will creep down. This explained why, while daily calorie restriction will work for a while, it often becomes less effective as time goes on. To quote a research study, “the vast majority of humans have significant difficulty “sustaining daily calorie restriction “for long periods of time.” In order to work around the fact that fat losses from daily calorie restriction are difficult to maintain, those who are into fitness will typically cut down to a goal weight and then begin gaining fat back in an endless cycle of bulking and cutting.
From a survival perspective, this makes perfect sense. If your body didn’t consistently calibrate its energy expenditure to bring it closer to what was available, long-term survival would be threatened. Take this study published in the New England Journal of Medicine. When subjects set a deficit to lose 10% of their body weight, total energy expenditure dropped by over 300 calories. The same way our muscles adapt to training by increasing in size, our metabolism can adapt to periods of increased or decreased energy intake.
Fasting, obviously, can’t result in this matching effect, though. It’s not like your body can drop your total energy burn down to zero which is why it instead pumps you with energy. My theory is that it does this to give you the best shot at finding food. Fast long enough, and, of course, studies show energy expenditure begins to drop, with one study showing a drop of 20% by the end of a 30-day fast. But for the first several days, it remains elevated, almost like it is taking a bet that you’ll be able to quickly find food. So there you have it. I could go on and on, but I think at this point, we’ve achieved our goal of providing a general overview.
We touched on aspects of hormones, metabolism, best practices, and criticisms, all with the actual research to back it up. Also, this channel just has 5,000 subscribers, so if you want to make sure you see my next video, consider subscribing or you may never see me again. Also, feel free to follow me on Instagram. Shoot me a DM, like all my pictures if you must insist. It’s up to you. And lastly, if you’re into science and nutrition, check out the kitchen tech startup I work at. We sell a device which uses precise heat control to automate cooking and take the error out for consistent results every time. The cooking method is called sous-vide. Imagine programming it to have a steak ready for right when you break your fast. My co-founders don’t even know I’m including this mention, but seriously, it’s very helpful if you have trouble getting a great result in the kitchen and don’t want to pay restaurant markups.
So if it sounds like something which would make your life better, I invite you to check it out. I linked it in the description as well. Okay, that was a long one. If you want to see my other fasting-related videos, I’ll put some links on this screen. And, as always, until next time, D-Man signing off. (light piano music).
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