A Comprehensive Guide to Fasting
Fasting has been part of the human experience from the start of our history.
Virtually every culture and religion around the world practices fasting in one way or another, and most environments have a natural rhythm that lead to seasons of feast and famine.
Whether driven by a change in the seasons, a drought, a plague of insects or times of war, our ancestors regularly experienced periods of hunger.
As a result, our bodies have evolved mechanisms to adapt and really benefit from times of lower food availability.
The benefits of not having a regular easy supply of food at all times are surprisingly varied. From the obvious impact on weight loss, to significant protection against cancer and many other diseases, fasting can have a powerful effect on our health.
But these days, with our global food supply and convenient lifestyles, we need to impose food scarcity upon ourselves to reap these therapeutic rewards.
What Is Fasting?Fasting is the process of abstaining from food in a deliberate and controlled way, for a specific period of time.
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Simply put, you just don’t eat for a while.
Different types of fasts can help you achieve different goals, and we’ll talk more about those options later in the post, but the data on fasting shows that there are benefits to all kinds of fasts, so no matter where you’re starting from, you’re going to see benefits.
Of course, most people have one big concern when it comes to fasting:
Won’t I be starving?!
In the modern world, hunger is a sensation that we really don’t have to deal with on a regular basis. We have a constant supply of food available to us, and so learning to navigate your hunger signals is an important new skill to develop as you start to practice fasting.
To many of us, when hunger happens, it signals a warning bell in our brain. Something feels wrong! And because it’s uncomfortable and unfamiliar, we scramble to fix it.
We end up eating very regularly, and so we don’t really ever have the whole experience of true hunger.
We snack between meals, often drifting mindlessly to the kitchen and eating before we even realize it’s happening.
How you eat and the times you eat are both very important for creating hunger signals in the brain, and when you change your eating patterns, you can expect to notice the sensation of hunger return.
This is a very good sign.
When hunger happens in a normal fasting situation, it comes on like a wave that you need to ride out. You might notice the hunger, feeling it build, and setting off those alarm bells in your brain. You might feel like it’s never going to go away, but then after a few minutes, it does. And it will get better over time.
One of the reasons I believe in incorporating fasting into your lifestyle is that it’s really simple.
It’s free, it’s convenient — you can do it while traveling or when you have a really busy schedule, it’s flexible — and you can take some time off from it without losing all the benefits you gained.
Fasting also helps you create balance.
Feasting and fasting is the natural cycle of life, and fasting allows you to fully participate in holidays, vacations and other important moments.
It’s a tool that allows you more freedom to be involved without taking a few steps back on your health.
Fasting is also the quickest way I know of to break through high insulin (traditionally called insulin resistance), breakthrough weight-loss plateaus, get rid of stubborn fat, lower cholesterol and blood pressure, and prevent Alzheimer’s disease and other chronic diseases.
It extends your life expectancy, increases longevity, and decreases inflammation. Your blood work will show a decline in all the markers for diabetes, metabolic syndrome, and heart disease.
There are many different types of fasts, and you can incorporate each different type into your lifestyle in order to make it sustainable.
Different Types of FastsAny type of fasting, whether it’s intermittent fasting or long multi-day fasting, creates all those benefits I just mentioned.
There’s no one best strategy highlighted in the research — the best strategy is the one that you follow and that fits with your lifestyle.
Longer fasts typically give you faster results but you do them less often. Shorter fasts take a bit longer to produce the results and are done more frequently.
Intermittent Fasting (IF)This is one of my favorite types of fasting, as it is really easy to keep up with. You can do it on a daily basis for long periods of time without sacrificing being involved in your normal life.
IF creates a healthy daily eating routine — it allows your digestive system enough time to rest between meals, which leads to healthier digestion. And when your body is not constantly focused on digestion, it can focus on healing and cellular repair and regeneration.
IF is convenient because you’re usually sleeping through the majority of the fast. There are a number of options for structuring your IF practice, with various fasting:feeding periods:
16 hours fasting, 8 hours feeding
18 hours fasting, 6 hours feeding
20 hours fasting and 4 hours feeding.
The main benefit of eating on a schedule like this is to support a healthy circadian rhythm.
Almost all of your body’s hormones are secreted daily, based on your circadian rhythm. You can think of hormones as your body’s internal messengers, so by using IF, you’re improving your body’s ability to communicate internally.
IF also helps us to develop healthy hunger levels. We’ve all gone on vacation or spent the holiday season eating more frequently over longer periods of time, later into the night, bigger meals — all that does is to increase your hunger over time.
It’s counterintuitive, but eating more doesn’t decrease your hunger.
Fasting, and specifically IF, helps break you out of that cycle when you’ve had a period of time like that (and that’s life, it’s going to happen). After a few days on IF, you develop a better routine and your hunger signals become clearer and under control.
There are two main hormones responsible for hunger signals.
One is called ghrelin, and as it increases in the body it increases your sensation of hunger. The other is leptin, and it makes you feel full or satiated after eating. Those hormones go up and down throughout the day in response to fasting or eating.
The main downside of IF is that many people chronically undereat when they do it for long periods of time.
When you do IF, you need to make sure you’re actually eating enough calories, because when you decrease your caloric intake over long periods of time, it can slow down your metabolism, which then sabotages weight loss efforts.
Sustained FastsSustained fasting is anything that lasts over 24 hours.
While IF can be a good fit for everyone — to prevent disease and make slow and steady strides towards your health goals — longer fasts are usually needed when someone has more severe issues they’re trying to tackle, like insulin resistance or obesity.
Of course, there’s another group that doesn’t have a severe health problem but wants to experience the accelerated benefits of autophagy, brain function, and fat loss.
The reason these longer fasts are great is that the benefits accrue quickly, but the downside is that there is a higher risk of complications.
You need to make sure that you’re working up to being able to do these longer fasts and that you’re working with someone who can help you monitor your progress.
There are a few ways you can do these longer fasts.
The 24-Hour Fast
In this model you start the fast after breakfast, lunch, or dinner one day and then end the fast before the same meal the next day.
The advantage here is that if you need to take medication or supplements with food, you can still take them daily, during that one meal.
If you prioritize having dinner with your family, you can still do that. If you want to maintain a social life and participate in evening events, this is a really great way to fit both priorities into your schedule.
The 5:2 Fast
On this plan you eat normally for 5 days of the week, and on the remaining 2 days you reduce your caloric intake to around 500 calories.
This is really effective for helping you to work up to a longer fast and getting your body used to that decreased caloric intake.
The Alternate-Day Fast
This model is primarily used to achieve a healthy weight. If fat loss is a main goal of yours, alternate-day fasting might be a good fit.
You fast every other day until you’ve reached your weight goal, and then switch to a different type of fasting to maintain your new baseline.
A research group from the University of Chicago followed an alternate-day fasting cohort for 12 weeks and found that by the end of the 2 months, the group experienced 11.5 pounds of fat loss on average and maintained all of their lean muscle mass.
The Multi-Day Fast
Once you get beyond about 36 hours on a fast — which you could put into your routine once a week — we’re really getting into the territory of extended or multi-day fasts, where you’re starting to see all those accelerated benefits that we talked about earlier.
One note I will make about multi-day fasts is that I don’t usually recommend people do 2-day fasts, because Day 2 is usually the most difficult day of a multi-day fast. One of the reasons for this is that ghrelin, the hormone that signals that you’re hungry, is peaking on Day 2.
After Day 2 it starts to decline and gets much easier, so you might notice that you feel the most hungry on day 2 and then it gets better. So if you can make it through Day 2, it’s better for your long-term fasting habit that you make it to day 3 so you start feeling much better and end on a positive note.
3-day fasts are great, because they are short enough that you can fit it into your schedule pretty regularly, depending on your goals.
Of course if you’re really keen to see as much benefit as possible, you can explore 4, 5, 7 or even 14-day fasts (fasts beyond 5 days should always be done with medical support on hand and be carefully managed to reduce the risk of complications).
(He was under close medical supervision for the duration of this crazy fast… don’t try this at home!)
What Happens In Your Body During A Fast
This is one of my favorite topics. There is a LOT going on inside your body when you’re fasting, but to really appreciate that, we need to first break down what happens when you eat.
When you eat, the food you ingest usually provides more energy than your body can immediately use, so some of the energy from that food has to be stored.
The hormone that controls the amount of energy used and stored is called insulin, and it’s like a key that unlocks your cells, where energy can be used or stored for later use.
Insulin also helps the body to store excess energy, beyond what can immediately be stored in the cells.
There are two main ways to store excess energy.
The first is converting energy to glycogen, which is a string of glucose molecules that are stored in the liver and muscles. There is a limit to how much glycogen we can store, so if there is still excess energy once your glycogen stores are full, the second option is for the body to store that excess as fat in the form of triglycerides in adipose (fat) tissue around the body.
Unfortunately, there is no limit to the amount of fat we can store.
Something that is commonly misunderstood is that these fat stores in the body are not just coming from the fat we eat.
It’s actually coming from carbohydrates and protein too. Carbohydrates and protein are broken down into glucose in the intestines, whereas fat digestion goes through a different process involving the lymphatic system. So when we’re talking about storing energy in the body, it’s coming from all the macronutrients that we eat — protein, carbohydrates, and fats.
So, back to fasting: one of the main goals people have with fasting is fat loss. In order to achieve that, you want to empty your cells of glucose and breakdown some of this stored fat. When fasting, your body switches from burning glucose (in the bloodstream and stored in the cells and liver) for energy to burning fat for energy.
Weight Loss When Fasting
Weight loss is one of the most common motivations for fasting, and one of the most obvious results too.
However, a lot of people misunderstand the process of weight loss during fasting, so I want to break this down real quick before we jump into the rest of the nitty-gritty details of what happens in the body during a fast.
Much of the weight that’s lost during a short fast is water.
This is because there is a direct link between eating carbohydrates and water storage in the body. When you eat carbohydrates — bread, pasta, crackers, baked goods, potatoes, rice, fruit and even vegetables — the body stores that energy as glycogen.
Your body packages glycogen with water, so early in your fast, when your body is breaking down all those packages of glycogen for fuel, the water attached to the glycogen is released into your bloodstream.
This makes you pee a lot and triggers a period of rapid ‘weight loss’ — up to 1 or 2 pounds a day in some cases — but this is not fat loss.
Fat loss during fasting averages around half a pound for most people. If you’re losing more than that, it’s probably just water.
So let’s go through, hour by hour, what’s happening in the body as you fast, so that you can see exactly where you can expect significant fat loss to kick in, as well as when you can expect the huge list of longevity benefits to ramp up.
Fasting Timeline0 – 4 Hours
From 0 to 4 hours after you eat a meal, you’re in Phase 1: the anabolic phase.
This is a growth phase, because you’re using the energy you just ate for energy and for cellular and tissue growth. Your pancreas secretes insulin and starts using up the glucose in your bloodstream and storing the excess in your cells.
4 – 16 Hours
From 4 to 16 hours, you’re in Phase 2: the catabolic phase.
This is the breakdown state, where you’re putting all those stored nutrients to use. This is the point where your glycogen stores are being broken down and used for energy.
Once those stores run out, your body switches over to using stored fat and ketone bodies for energy — this usually happens towards the end of the 16 hours.
So, if you’re doing intermittent fasting with an 8-hour eating window and a 16-hour fast, you are basically staying within these two phases for the entire fast.
And if you’re wondering how long it takes to get to that fat-burning stage at the end of phase 2, it really depends on what you’ve eaten. The higher your diet is in carbohydrates and starch, the longer it’s going to take to burn through those stores and reach that fat-burning stage.
That’s why I always recommend that if you’re about to start a fasting protocol, you reduce the amount of carbohydrates and starches from what you normally eat. You don’t have to cut them out completely, but reducing your intake will help you reach fat-burning faster.
Another really cool thing that happens during Phase 2 is that the growth regulator called mTOR goes down, which opens the door to a process called autophagy.
Autophagy is one of the main benefits of fasting: it’s a cellular clean-up, which helps the old and malfunctioning cells to be mopped up and removed from the body. This phase is so powerful because autophagy removes cellular material that can be contributing to aging, cancer, and chronic disease.
16 – 24 Hours
Between 16 and 24 hours, you enter Phase 3: the primary fat-burning stage.
At this point, your body is burning your fat stores to keep up with your energy demands, because you don’t have any glucose left.
There’s also an energy sensor that gets triggered during this phase called AMPK.
AMPK presses the gas pedal on autophagy and really dials up the amount of autophagy going on in the body.
24 – 72 Hours
Stage 4 kicks off between 24 and 72 hours: this is the ketosis stage.
This is where your body has switched over completely to burning fat for energy. Ketosis is the process of your body splitting fat cells to release energy, which produces ketone bodies and ramps up all the benefits of the previous stages.
Ketone bodies act as fuel for the brain when glucose is scarce.
It’s important to note that nutritional ketosis, from fasting or low carb diets, and diabetic ketoacidosis, a potentially life-threatening condition, are not the same thing!
We have this built-in mechanism that during times of food scarcity, we are still able to supply energy to the brain in order to function and make good decisions, which is pretty amazing.
Many people, myself included, have experienced significant improvement to their energy and mental clarity during this phase of a fast or when following a ketogenic diet, and it’s these ketone bodies that are putting you in that state.
Another really cool thing that happens around the 24-hour mark is that your brain produces a chemical called brain-derived nootropic factor (BDNF).
BDNF supports the growth of brain neurons and is really important for long-term memory, coordination, and learning.
Researchers think that it’s probably a key part of why fasting is so effective for reducing our risk of Alzheimer’s disease as we get older.
During fasts that last more than 72 hours, you go into a deep state of ketosis, which amplifies all the previous stages.
You’re getting all the benefits of weight loss, metabolic health and longevity really compounded as time goes on.
With multi-day fasts, insulin levels and glucose remain low and you stay in a steady state of ketosis.
Due to the lack of nutrients, your liver reduces the production of IGF-1 which is a hormone involved in growth and development.
Short-term decreases in IGF-1 are associated with low oxidative stress and are likely anti-cancer and anti-aging.
Fasting of 72+ hours is also shown to improve the body’s response to toxin exposure and stress hormones.
How To Choose the Best Type of Fast For YouAsk yourself… what is your current diet? If you are eating a typical diet higher in starches and sugars then start small with IF.
If you have been following a ketogenic or lower starch/sugar diet you can probably handle a longer fast. Make sure you have a doctor who can support you through it.
Think about what will work best for your lifestyle. Set yourself up for success — start slow and you can always build upon it. If you’ve never done any fasting, start with IF and slowly reduce the feeding window over the next couple of months.
Common Concerns About Fasting
Most people have some concerns when it comes to implementing fasting into their lifestyle. This is totally normal, and so I want to spend some time here addressing the most common concerns.
The first, of course, is about hunger.
Managing Hunger During A Fast
Remember that hunger is a hormonal signal — a data point. More often than not, hunger is a state of mind more than the state of your stomach.
Eating in response to hunger is a learned response, and while it takes a while to change that habit, you are not obliged to eat just because your body sends a signal.
As your body becomes more accustomed to fasting, it will become more fat-adapted, meaning that instead of just burning glucose for energy, you start to burn fat instead.
This process takes some time, so to help manage your hunger, your last meal or two before going into your fast should ideally be lower carb, as this will help the transition to burning fat instead of glucose go more smoothly.
It’s important to stay ahead of thirst — stay hydrated, and if you’re having a lot of activity in your digestive system (like growling or pangs), carbonated water is really effective for settling that down. Coffee — regular or decaf — has also been shown in research to suppress hunger for some people.
Another option is adding salt to your water.
This is a magical tool — if you’re feeling really low-energy, a little shaky, or you’re not sure you can continue, as soon as that feeling starts, you need more salt.
Studies of prolonged fasts have found no evidence of electrolyte imbalances in the blood, however, salt is still a great tool to reduce hunger.
You can add a teaspoon of sea salt to some water, you can chew on some coarsely ground salt to bring yourself back to equilibrium. I also really like the LMNT hydration packets.
There are about 1.7 grams of sodium in a teaspoon of pink Himalayan sea salt. Two to three grams of sodium daily is a good starting point around day 2 of any fast due to the increased loss of sodium that happens through the urine while fasting.
*If you have a health reason for avoiding salt or if you are on blood pressure medications make sure to talk to your doctor before undergoing any fasting protocol.
Don’t forget that exercise is a really powerful appetite suppressant.
People often assume they shouldn’t exercise during a fast, and while I don’t recommend very high-intensity workouts, exercise directs blood away from the digestive system and into the muscles, which helps to quiet that hunger signal.
If you’re having symptoms of irregular blood sugar levels, some green tea with cinnamon is a useful aid as cinnamon can help regulate blood sugar.
And if you’re struggling with that inner voice that’s telling you this is too hard, you should stop, it’s too much, then a meditation or mindfulness practice can be extremely useful in quieting that voice so you can carry on (assuming you’re not actually experiencing any extreme symptoms that would indicate that you should change what you’re doing).
My favorite tools for meditation and mindfulness are Headspace, Calm, the Muse brain-sensing headband, and 10% Happier.
Regular fasting can help to improve your sleep quality over time.
It is very important to prioritize sleep while you are fasting because when you don’t get good sleep, your body releases a different set of hormones that will make you feel more hungry than usual.
You want to shoot for 7 to 9 hours of solid sleep that is deeply restful and uninterrupted so that you’re not risking worse hunger than is necessary.
If you need a fantastic tool to help track your sleep and the changes to your health during your fast, read about my favorite health tracking device.
However, it is common to experience some sleep disruption when you are new to fasting. Read below for my favorite form and dosage of magnesium to help with sleep.
Energy and Brain Function
Most people report that when they’re fasting, their mental clarity and energy levels are actually better than usual.
Keep an eye on your energy and brain function as you experiment with different types of fasting — are you high-energy in the morning and then seeing a dip in the afternoon? Then schedule all your important tasks for the morning and give yourself less demanding stuff when you’re in that dip.
Observe how your particular body responds to your fasting protocol, and schedule your days accordingly.
Discomfort and Symptoms
It’s fairly common for people to report dizziness and/or headaches when fasting. This is brought on by dehydration and a lack of salt. Most of the discomfort with fasting can be avoided if you are well hydrated and taking regular salt.
If you’re getting constipated or your bowels are slowing, which is common on multi-day fasts, make sure you’re eating enough fibrous fruits and vegetables during your non-fasting days, and supplement with magnesium. Magnesium helps with relaxation, muscle cramps, constipation, sleep quality.
I recommend taking 400-600 mg of magnesium citrate daily to keep your bowels regular or magnesium glycinate if you are having difficulty with sleep or headaches. Click the image below to create an account with Fullscript to gain access to the highest quality professional-grade supplement brands.
If you get heartburn after your fasting period, make sure that you’re eating slowly, chewing your food thoroughly, avoid large meals and avoid overeating.
Make sure you stay upright for a while after meals — don’t go to bed or lay down immediately after eating.
The more you fast, the more you’ll develop a sense of what’s worth pushing through.
You’ll get more familiar and comfortable with the signals your body is sending, and so you’ll be more able to identify when to persevere and when it’s time to take a step back, try something different or try again later.
Exercise and MovementKeep exercising and incorporating movement into your daily routine during your fast.
If you experience unusual discomfort during exercise, it’s usually a sign to dial it back a little bit — it doesn’t need to be as high intensity as you might usually go for.
Make sure you’re hydrated and have enough salt, especially if you’re sweating during the workout.
Blood Sugar and Blood Pressure ManagementIf you’re on blood sugar medication or struggle with blood sugar issues, make sure you work with your doctor and test your blood sugar regularly throughout your fast. Your medication dosages may need to change during your fast. Your blood pressure can go down when you’re fasting, so you want to track both components to make sure they’re staying within a safe range during your fast.
Fasting MythsIf you fast, or intend to, there are a few myths that you’re going to run into. I hear these 5 myths all the time, and it’s important to go into this lifestyle change with the knowledge of what’s true and what’s not.
Fasting Myth #1: Fasting puts you into starvation mode and decreases your metabolism.Metabolism is measured by BMR — your basal metabolic rate. This measures the amount of energy your body burns to keep all your organs functioning optimally.
When your BMR goes up, your metabolism goes up. This supports healthy weight maintenance and weight loss when necessary. When your BMR goes down, your metabolism goes down, and this can lead to difficulties with weight loss or a weight loss plateau.
Your BMR goes up naturally when you’re cold — your body has to shiver to maintain heat — and your BMR goes down naturally when you reduce your daily intake of calories. This doesn’t happen after one meal; it happens when you’re running at a caloric deficit for a long period of time.
This is why in some cases, you may have heard from a doctor, nutritionist or health coach that in order to lose weight, you actually need to eat more.
It’s counterintuitive, but it’s true.
When you experience reduced metabolism, you feel cold, tired, hungry, and have low energy. If you are already experiencing those things, you may need to first spend some time repairing your metabolism and getting your food intake back on track before jumping into fasting.
Fasting Myth 2: Fasting makes you lose muscle mass.This is the first concern I hear from clients who want to build or maintain their lean muscle mass.
They’re worried when I suggest adding fasting to their routine, because they’ve heard so many times that when you’re fasting, your body breaks down muscle to use for energy.
In just about all cases, this is not going to happen. The hierarchy of how your body converts fuel to energy is that first you burn glucose, then you burn fat stores, then you burn muscle.
Your body will not start breaking down muscle tissue until your fat stores account for less than 4% of your total weight.
To put that into context, elite male marathon runners — who are extremely lean — have a body fat percentage of around 8%.
So for most of us, we’re never going to get to a place where our body is going to start breaking down muscle tissue for energy.
When you’re fasting, your body actually conserves muscle. Fasting triggers the release of growth hormone, which helps you to build your lean muscle mass.
During the fast, your muscles might feel a little deflated or look a little smaller, but this is due to water loss, and it will come back once you get more hydrated.
If you’re trying to continue building muscle while fasting, you have to exercise. There’s no other way to do it.
Regardless, exercise and daily movement are paramount: things like weight training, bodyweight training, yoga, walking, biking — all these things will help your body build and maintain muscle mass when you’re fasting.
Fasting Myth #3: Fasting causes low blood sugar.While you might experience some symptoms of low blood sugar — like shakiness or feeling ‘hangry’ — those usually only happen when you first start incorporating fasting into your lifestyle.
If you are prone to hypoglycemia or if your diet is very high in sugar or starch going into the fast, that can cause some blood sugar issues.
But once you become fat-adapted — when your diet is a good fit before your fast and you start to burn fat for energy easily — your body will have all the nutrients it needs to keep a steady balance while burning fat and running on ketone bodies.
Fasting Myth #4: Fasting results in overeating.This is something that many people are afraid of, and studies do show that when you first start fasting, there is an increased risk of overeating, particularly if you’ve ever had any kind of disordered eating in the past.
Fasting can trigger your old habits so if that’s your situation, it is important that you’re working with a therapist to make sure that this change doesn’t lead you down a bad path. For many people with a history of eating disorders, fasting is not going to be a good fit.
However, if you have not experienced disordered eating in the past, it’s normal that your hunger hormones won’t have fully regulated in the early stages of a fast.
This can make you want to scarf down everything in sight after your fasting window ends.
I’ve been there before too, but I would argue that it’s usually a sign you’re not ready for that length of fast or that you need to go into the next one with your diet a little more dialed in.
Fasting over the long run actually helps to reset the hunger hormones — the leptin and ghrelin that we talked about earlier — and your appetite becomes more stable over time.
Fasting Myth #5: Fasting leads to nutrient deficienciesActually, the opposite tends to happen.
Your body reduces the excretion of vitamins, minerals and the by-products of broken-down fat and protein during a fast. And because you have less bowel movements (particularly with those longer multi-day fasts), you’re losing less through your stool as well.
Electrolytes, magnesium, potassium, calcium, phosphorus and so on all remain stable during longer-term fasts.
The only time that micronutrients — vitamins and minerals — become a major problem is when you’re chronically deficient in those nutrients already and you’re doing a longer multi-day fast.
In that case, you may want to take a multivitamin, and for this I recommend a supplement called Primal Multi by Designs for Health. Click here to create an account with Fullscript to gain access to this pharmaceutical-grade supplement. If you are located outside of the US, Thorne’s Basic Nutrients 2/Day is my favorite.
Tips To Get Through A FastIn this section I want to share 10 of the tips and strategies that have proven really effective for helping you get through a fast, whether that’s intermittent fasting or a multi-day fast.
1. Drink water.I really can’t emphasize this enough. The minute you start getting even a little bit dehydrated is when you’re going to notice hunger symptoms and discomfort kicking in.
Start each morning with a big glass of water and keep a water bottle with you at all times through the day. Put sticky notes up around your house, set a reminder on your phone — do whatever you can to remind yourself to keep hydrating.
2. Stay busy, and change your daily routine slightly.Our daily routines are really linked to hunger signals, so it’s a good idea to change things up, especially early in your fasting practice.
Give yourself a reward each day by doing something you might not otherwise do, to change up the rhythm of the day.
That might be going for a walk, getting a massage, taking a nap or meeting up with a friend — anything that you really enjoy doing and that feels like a reward should be fit into each day.
3. If you’re already a coffee drinker, keep drinking black, unsweetened coffee throughout your fast.I wouldn’t start drinking coffee if you don’t already, but if you do, it’s a really effective appetite suppressant.
The only reason you would stop if you are a coffee drinker is if your goal is complete digestive rest, but if your goal is weight loss or longevity, coffee is fine.
4. Ride the wave of hunger.Remember that hunger doesn’t last forever — it will hit you, and then, like a wave, it will recede. When it does hit, you want to drink water, sparkling water, tea, or coffee.
Change your environment — go for a walk or do something to get your mind occupied with something else until that moment of hunger passes.
5. Don’t tell everyone you meet that you’re fasting.Be selective with who you talk to, because not everyone is familiar with the benefits of fasting or why you would want to fast, and their lack of support or negative reactions can feel very discouraging.
Only involve people in the process who understand what you’re doing and are going to be supportive.
6. Give yourself a month to get used to fasting.Fasting is like any other life skill — it takes practice. If you’re new to this, give yourself some time to figure out what type of fasting your body really benefits from, how your body responds during a fast.
Experiment a lot and give your body time to get used to different types of fasting.
7. Work on improving your diet during your non-fasting period.Remember that fasting is not an excuse to just eat whatever you want afterwards — you still want to practice healthy eating and keep improving your diet over time.
When you change your diet and you start fasting, that’s when truly amazing things can happen in your health.
8. Have a protocol in place for when you break your fast.We’ll talk about this more below, but it’s important that when you break your fast, you don’t just go on a binge and eat everything in sight.
Carefully plan your first meal, and then work out how you can return to eating normally without a big blow-out after the fast. My favorite way to break a fast is with some broth or chicken soup.
9. Fit fasting into your life.Try not to change your life to fit a fasting schedule — instead, you want to change your fasting schedule to fit your life.
It’s much more sustainable doing it this way, because your fasting practice is not coming into conflict with your other commitments and priorities.
Determine if you have any non-negotiables in your life. It could be work schedules, family commitments, travel plans, and things that happen on a daily basis, and then experiment until you find a style of fasting that works with those commitments.
10. Start slow, and adapt your fasting strategy often.As I’ve said, the first month of fasting is really one big experiment to figure out what works for you. But you want to keep experimenting and tweaking even beyond that time to keep observing what’s working for your body.
Your body will change over time, and so your fasting practice should too.
When To Change or Stop Your Fast EarlyFasting is always going to create some physical discomfort. It’s totally normal to experience hunger (often far more intense than you’re used to), as well as plenty of other symptoms.
Many people report headaches, dizziness, achy joints, nausea, brain fog and disruptions to body temperature when fasting.
To an extent, all this is normal, and usually the discomfort will pass in a short period of time.
Fasting is like being in a shallow pool: if you get worried, you can just put your feet down (and eat!). Everything will be fine as long as you don’t panic.
However, sometimes your body may not respond well to a particular fast. This can be the result of eating too many starches and carbs right before starting the fast, or it can be a consequence of increased stress or some other issue going on with your health.
So if you are experiencing sustained, persistent symptoms, then it might be time to reassess this particular fast. Vomiting or ongoing nausea, fatigue, or brain fog are clear signs that you should take a step back and try something different.
If you are doing a multi-day fast — longer than 24 hours — you should always do so with some medical supervision or support. Inform one or two trusted people in your life (such as your partner or close friend) about your fast so that they can support you and help you make the decisions that will be right for you.
How To Break A FastThe most important thing to keep in mind when breaking your fast is to do it gently. The longer you’ve been fasting, the slower you need to take this.
There is a natural tendency after fasting to dive right back into food and to overeat, and that can lead to a lot of stomach discomfort and create a lot of discomfort.
Don’t just dive into a pizza, especially after a longer fast, because it’s going to be quite painful!
If you’ve been fasting for 24+ hours, you want to start with a small snack, wait 30 minutes, then take an assessment of how you feel to see if you’re still hungry.
Make sure to eat slowly, chew your food really thoroughly. Try something light, like some avocado, a small piece of fish or some vegetables cooked in olive oil.
I would avoid raw food in general, as that can be harder to digest. If you have trouble with eggs or another type of food (or you’re not sure how they affect you), I recommend waiting a couple of days until your digestive system has warmed back up.
And of course, avoid any high-sugar food, highly-processed food, and any foods you know you have an intolerance to.
If you’re really craving sweets, try some fruit: berries or an apple can be a great option.
I almost always break my own fast with a broth or soup. I have a chicken soup recipe that is my cure-all for everything — I use it to reset my hunger, to calm my digestion, to get through a cold or flu, reduce bloating or get back on track after a period of overindulgence — and you can find that recipe here.
If you’ve been doing a multi-day fast, it will usually take about half the number of days you fasted for your digestive system to return to normal.
Don’t forget to keep drinking plenty of water once your fast is done, as that will continue to help your health in all areas.
* * *
Fasting is a lot like exercise. At the beginning, you’re going to feel a bit sore. But the more you do it and the fitter you get, the easier and more routine it becomes.
The more experience you have, the more you’re going to feel like fasting is a much-needed break from food.
Of course, food is one of the greatest joys life has to offer and it should be.
Food is culture, it’s family, it’s celebration — and fasting allows you to participate in all of those parts of life without anxiety and food guilt.
It allows you to live your life fully, without losing the progress you’re working so hard to achieve.
It empowers you to heal your body in a sustainable way, and to take your future health into your own hands.
Fasting is an incredible tool that can have a truly transformative impact on your health.
I encourage you to start experimenting so you can enjoy the myriad of benefits it can create. And if you want help creating the most effective and safest protocol for you and your health, click here to work with me.
I really enjoyed this article. I have been fasting for 4 months with ease. I am slowly moving from 16 hour fasts to 24.
As far as autophagy goes if you do several shorter fasts will the autophagy be equivalent to a longer extended fast? Or will certain things only go through autophagy at longer extended times for fasting?
This is covered above: 16 to 24 hours: you’re in the fat-burning zone and autophagy ramps up
I’ve read if you want to boost stem cells naturally, it takes three days for that to happen. I’m guessing fasting for 6 hours for 12 days won’t do it.
I am currently in my second multiday fast. The first was 3 days, now I am going for 4. Do you think it would be OK if I did a multiday fast once a month. I am overweight … bmi 31, am 60 yo, otherwise my health is fine. I am worried about my waistline, so that is the motivation for the longer fasting … hoping for some benefit with autophagy as well.
I have found the multiday fast to be so easy , not even hungry … am tolerating this very well.
Thorough, wonderful resource! Thank you:)
Great article. I’m 5 days into my first 14 day fast., but I’ve been on OMAD low to near no carb diet for 2 months and well positioned to begin the fast. Day 3 I saw my blood glucose declining while my ketones increased. So far hunger hasn’t been an issue aside from psychological response hunger. I have my exit strategy all planned out for day 14. My only questions are is there a low glucose trigger level and if so what is the proper response? I’m not really concerned about that though. I have enough body fat to keep 3 people going on a fast. Also, at two weeks fasting do you really see a need to notify a doctor? Again, great article. Aligns with everything I’ve learned so far.
Sorry, doc. Forgot the main reason I read your article. For extended fasting, a week or more, is there a suggested interval between fasts? I’m on a long haul weight loss program. I may to face surgery and they were clear that losing weight would be preferable.
thank you for this very informative article!
I’ve been doing 16-8 fasting for about three months and it’s been great for me. I’m a type 2 diabetic and in
five months I’ve gone from 85 kg to 70 and according to my doctor I no longer have diabetic test results from my blood. I recently decided to try an extended fast and I’m currently 87 hours in. I must say it was way easier than I anticipated. Probably because I’ve been IF so long. I feel great and my blood suger is lower than ever in a positive way. It’s gonna be really interesting to see if my body (blood sugar) will react differently to food after this.
I’ll save this article for my next fast cause it will prove really helpful reminding me what’s important!
thank you, this is the exact reason why I am starting a fasting lifestyle. I was recently told that I have crept into diabetes 2 category which I wasn’t happy about so will now carry on after reading your comments
This is the MOST helpful, insightful article I have found for IF. Thank you.
Thanks good word and encouragement. I was not sure to keep working out and it looks like I can but maybe not as hard.
Thank you for the article! It is very informative and I appreciate the time you took to write this up. I have shared and have received lots of good feedback!
This is an awesome and informative artivle. Thank you for compressing all the recent finds, facts and eliminating the myths about fasting all in this one article. I am on my 3 rd fast (7 day, 3day, 3day) and although my goal is to maintain ketosis, I cannot say enough about the clarity in my thinking and… …quelling of anxieties. I can mentally multi-task better, plan for uncertainties more calmly and speak my mind more accurately and without distracting reserve, while fasting. My communication with my spouse has become more honest and pleasant because I am not overthinking the results of the truths of my feelings. I cannot praise fasting enough and articles like youre really sum up the pro’s and cons accurately. On a side note, I am a transplant patient. My numbers after fasting (bloodwork) look better that when I first received my transplant over 12 years ago. I am working on weight loss, long-term, and fasting is the best option – even over surgery(according to my results, personal experience and my healthcare team). Thank you again Dr.Shields and may you see the best results in your personal life for such benevolent articles.
This page really couldnt be more helpful
Such an easy to understand and infoyarticle. Thank you so much
This was a decent and informative read, thank you very much. I have recently tried to eat dinner around 6pm (work depending) and often miss breakfast in order for the first meal of my day to be lunch at 1pm – giving me a 18-19hour fast.
I used to force breakfast down thinking I needed the energy for the day, but I am happy for the change and this article shown why. Currently trying to lose some stubborn lower tummy fat whilst maintaining my muscle mass and drop my body fat a few percent. I will perhaps try and build up to a 24 hour once or twice a week. Thank you for the advice.
Hey. How often should we be doing a 5 day fast? Thanks Vanessa.
Hands down the best article on Fasting I have read, Thank you
What a wonderful article!! Thank you for sharing it! I absolutely love and cherish fasting! It’s so so good!! I would put meditation and breathwork as the number one fasting party favor! Higher vibe thoughts add energy and I find lower vibe thoughts or consuming lower vibe external reading or viewing has lower energy drag to it. Everything is so much more noticeable during a fast and this energy awareness keeps on giving after the fast too. So epic. It’s such a beautiful delicious journey every time! Yum
Excellent article. I’ve been vegan 33 years. It’s not so easy to be healthy now, not only am I older, 57, but there are so many sugary and processed vegan foods in the grocery store now that I have found it harder to not eat junk. I intend to get rid of my waistline and go back to healthy eating with fasting. I am sitting on 30 hours right now and was thinking about a banana. Reading your excellent article, I’ve decided I’ll go out and do some gardening instead, get some exercise and let the thoughts of food and eating pass for a bit longer. Thank you.
Thank you for the empowering, all encompassing information! I’ve been fasting for 2 1/2 weeks drinking water and chicory blend of coffee with honey and almond milk. About a week into it my system became highly acidic, so I stopped coffee (I realized the honey was causing the problem). Began drinking much more water and would awake feeling dehydrated & low energy. Your tip to drink salt water REALLY made an instant positive impact on stabilizing my energy level. Thank you so much! I plan on fasting for an extended long term period and I am confident with the information that you provided that I can do it!
This is one of the best articles on fasting I’ve ever read. Very thorough and I love the myths and tips you included. Thank you!
This is one of the most comprehensive and informative article on fasting i have ever seen. Thanks for putting it together. Excellent information and great attention to detail. You have covered all aspects.
The post above is extremely thorough, comprehensive and professional. I have learned a lot from it that i have never seen anywhere else. Thank you Dr Alexis for the time and effort you have put into this post to help your readers. I am 76 years old, and have had Diabetes 2 for about 20 years, and high blood pressure since age 21 with continuous medication since age 24. I have had most of all of the many symptoms of Metabolic Syndrome for many years.
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25 replies to "A Comprehensive Guide To Fasting"