How to Prepare for Fasting: An In-Depth Guide

Written and medically reviewed by Nicole Grant, RD

Fasting seems fairly simple, right? You eat, or you don’t eat. However, how you prepare for a fast can change your experience — both the way you feel during your fast, and what your body is accomplishing.

Why Is Preparation for Fasting So Important?

While there are many benefits of fasting, there are also several factors to consider and steps to take when thinking about how to prepare for fasting. Your nutrition, exercise, and mindset can all influence how you feel during a fast as well as your chances of successfully completing the fast. 

Preparation for fasting also helps get your body, mind, and metabolism in the right state to provide even quicker benefits from fasting.

Takeaway: Preparation increases your chances of successful fasting.

How Should a Beginner Plan to Approach Fasting for the First Time?

First, decide how many hours you want to spend fasting. Don’t shoot for the stars (e.g., an extended 7-day fast) — you have plenty of time to work your way up if that’s your ultimate goal. Instead, start with shorter fasts. A circadian-rhythm fast, which consists of 13 hours of fasting, can be a great place to begin. Practice this for a couple days before taking the next step of gradually working your way up to longer intermittent-fasting routines (with approval from your doctor, of course). Also, make sure that you’re in good health and have no prior health conditions (like type 1 or type 2 diabetes) or notable risk factors (like a history of disordered eating) that could make fasting inadvisable. 

Finally, set yourself up for a successful fast with the right preparation. You want to make sure your periods of fasting are working to optimize your weight loss and longevity and promote a healthy lifestyle. To do this, consider your food intake — what you do and don’t eat — as well as your hydration, physical activity, and mental state going into a fast.

Takeaway: Give yourself ample time to ease into a long fast.

How to Eat and Drink When Preparing for a Fast

People can approach nutrition in different ways, and there is really no “one best choice” for fasting. But in preparation for fasting, it’s always important to take a closer look  at your eating routine. You can make fasting feel easier — and potentially achieve even greater benefits — by consuming certain foods and beverages and avoiding others. For example, a final pre-fast meal that’s very processed and high in salt will not support your health goals as much as one with nourishing, minimally-processed foods.

One goal of fasting, which you can encourage through what you eat before your fast, is to get your body into a flexible metabolic state. More simply put, you want to choose foods that help stabilize your blood sugar, which in turn allows your body to more easily switch between fuel sources such as glucose and fatty acids. As a result, your body will be able to tap into your own fat stores for energy during a fast, leading to more stable energy while fasting and an increase in long-term weight loss.

In general, whole foods that are minimally processed will have the best impact on your metabolism. Below are some specific foods you can include in your daily meals.

#1. Non-Starchy Vegetables

Starch is carbohydrate, so starchy vegetables have more carbohydrates that can elevate your blood sugar. Therefore, when thinking about how to prepare for fasting, you want to emphasize non-starchy vegetables to help keep your blood-glucose levels in check. Starchy vegetables include potatoes, sweet potatoes, acorn squash, and butternut squash. Most other vegetables are non-starchy, such as lettuce, green beans, cauliflower, broccoli, and cucumbers.

#2. Fiber from Whole Foods

Fiber is a great way to balance your meals and optimize your metabolism in preparation for a fast. It is estimated that around 90% of the US population does not consume the recommended daily intake for fiber. Therefore, during the week or two leading up to your first fast, start increasing your fiber intake by a few grams per day. (Doing this gradually, rather than suddenly, will be kinder on your digestive system!) Choose fiber in its whole-food form, so you can capture the benefits of more vitamins and minerals. Examples include vegetables (both starchy and non-starchy), low-glycemic fresh fruit (not fruit juice) such as berries, beans, nuts, seeds, and whole grains like quinoa and steel-cut oats. 

#3. Protein

Each meal you eat in preparation for fasting, and your last meal in particular, should have a protein source. This provides amino acids for muscle growth and maintenance. Certain amino acids are considered essential, meaning you can only obtain them through food. Since you are not eating during a fast, you want to make sure you are getting enough essential amino acids from food prior to your fast. In addition, protein sources such as chicken, eggs, fish, nuts, and dairy provide a satiating component that keeps you feeling fuller for longer and encourages more metabolic flexibility going into a fast.

#Healthy Fats

In addition to carbohydrates, your body can use fat and fatty acids to produce energy. When thinking about how to prepare for a fast, consider that more energy from fat (instead of carbohydrates) will keep your blood sugar under control and help your body transition into a fasting state more easily. For longer fasts, consider swapping some processed carbohydrates — such as crackers, cookies, breads, and pastas — with more healthy fats like avocado, olives and oil, nuts, seeds, and seafood. 

Hydration is also important when thinking about how to prepare for fasting. The amount of fluid you need in a day depends on a variety of factors such as your body size, age, physical activity, and the environment where you live. However, as a general rule, studies indicate you typically need between 25–35 milliliters of fluid per kilogram of body weight. For a person weighing around 200 pounds, that would equal about 2,200 to 3,200 mL per day, or about 9–13 cups of water. In addition to plain water, black coffee, green tea, herbal teas, sugar-free sparkling water, and bone broth are great options to drink leading up to your fast.

Takeaway: Focus on a healthy diet full of unprocessed ingredients and beverages.

Things to Minimize or Avoid Before a Fast

As mentioned above, it’s important to choose foods that help your metabolism stay flexible during a fast. Conversely, there are also options that make metabolic flexibility more challenging and can cause unpleasant symptoms during a fast.

Here are several to watch out for.

#1. Added Sugars

An added sugar is one that is added to food during processing. Cane sugar, brown-rice syrup, high-fructose corn syrup, and dextrose are common examples found in many packaged foods. In excess, these added sugars not only contribute to more inflammation in the body, which can diminish some of the benefits from fasting, but they can elevate blood sugar and make it more difficult for your body to achieve a fat-burning state. 

#2. Highly-Processed Foods

Highly-processed foods typically come in a package, are made in a factory, have a long list of ingredients, and contain added sugars and unhealthy fats. Fast food, boxed pastries and desserts, and many crackers, soda, frozen foods, and chips are considered highly-processed foods. One reason to avoid highly processed foods as you prepare for a fast is because of their negative effects on your blood sugar and metabolism. Additionally, by consuming mostly highly-processed foods, you will have lower vitamin and mineral stores to sustain you through a fast, and your body will have a harder time switching to a fat-burning state. Finally, research has shown that consuming ultra-processed foods leads to higher caloric intake, making weight loss more difficult.

#3. Too Much Caffeine

While most fasting allows for black coffee and unsweetened tea, if you plan on practicing an intermittent-fasting protocol that requires you to drastically minimize or completely eliminate caffeine (such as water fasting or fasting for gut health), you may want to taper down your caffeine intake a few days prior to your fast in order to minimize symptoms of withdrawal. Some people experience withdrawal symptoms from the removal of only 100 mg of caffeine, or about 1 cup of coffee! Many people drink more than that, so consider slowly tapering off your caffeine intake during the 2–9 days before an extended fast. 

#4. Excess Alcohol

During an intermittent-fasting protocol such as the 16:8, it’s ideal if you avoid or consume zero alcohol; this applies to both your fasting and eating windows. Alcohol is calorically dense, containing 7 calories per gram — almost as calorically dense as fats. In addition, alcohol is perceived by your body and your cells as a toxin, and it cannot be stored; therefore, your body will prioritize the burning of alcohol above all other fuels, dramatically slowing your fasting-zone progression since you will not be able to burn through your glycogen stores and shift into fat metabolism until your body processes the alcohol effectively.

Lastly, alcohol is known to alter your blood-glucose levels, which can lead to cravings or increased interest in late-night snacking. Updated research indicates even moderate alcohol consumption may be counterproductive to your long-term health goals. Alcohol should be avoided during your pre-fast meal whenever possible.

Takeaway: Minimize added sugars, highly-processed foods, caffeine, and alcohol.

Supplements to Help You Prepare for a Fast

There’s no one-size-fits-all approach to supplementation, even in preparation for a fast. Daily supplements should be based on what you need in excess or what you may be lacking. For example, someone who doesn’t eat fish may want to take a fish-oil supplement, or a bodybuilder may want to consume additional branched-chain amino acids (BCAAs) to support muscle growth.

One type of supplement, electrolytes, are likely beneficial for most people during a fasting routine, especially a fast that may last a few days. Check out the next section for more details on that!

In preparation for fasting, it’s usually a good idea to continue your daily supplement routine and potentially add in electrolytes. However, consider speaking with your doctor or dietitian to figure out which supplements are best for you and if there are any special considerations or concerns for your personal needs.

Takeaway: Continue taking your daily supplements.

Don’t Overlook Electrolytes Before and During Your Fast

Electrolytes, such as sodium and magnesium, are an essential part of nutrition. They help the human body perform daily tasks like regulating nerve and muscle function, transporting nutrients, and maintaining hydration

In addition, electrolytes can help combat some of the side effects you may experience while fasting. During a fast, especially an extended fast, you’ll start to lose sodium and magnesium at a faster rate than when you’re in a normal, fed state. On top of that, because you aren’t getting your normal electrolyte intake from food, supplementation may become necessary. Needs vary person to person, but typical starting ranges of 2–3 grams of sodium and  400–600 mg of magnesium per day tend to be appropriate for most people.

Takeaway: Additional magnesium and sodium may be needed, especially on an extended fast.

How to Exercise When Preparing for a Fast

For the average person preparing for a fast, the need for a drastic change in exercise is unlikely. Continue a blend of cardio, weight training, and restorative exercises most days of the week. Why most days? Daily movement leading up to a fast puts your metabolism in a better place and sets you up for a better chance at weight loss (if that is your goal). 

Timing a workout around your fast can also provide additional benefits. Traditionally, a morning exercise routine works for most people. If you are following a time-restricted feeding pattern such as a 16:8 routine, a fasted workout in the morning (i.e., no food before exercise) will provide metabolic benefits such as burning more fat as your workout fuel.

If you are an evening exerciser or want to do an extended fast, that works too! In this case, consider timing a workout immediately before your fast begins. Exercise encourages glycogen depletion, which will speed up your transition to a fat-burning state. Therefore, adding a workout right before you start a fast can help you see those benefits quicker.

Takeaway: Time your workout around your fast.

How to Mentally Prepare Yourself for Fasting

Decide ahead of time what type of intermittent-fasting routine you will follow, especially the duration and the frequency. The type can vary anywhere from a 13-hour circadian-rhythm fast to a multiple-day water fast. The frequency can be every day or a couple of times a year for a prolonged fast. Typically, a time-restricted eating pattern can be followed daily or multiple days a week, whereas you would probably do a multiple-day water fast only a couple times a year. Whatever type and cadence is right for you, decide ahead of time so you know how to prepare appropriately.

Adopting a new intermittent-fasting routine isn’t always easy. You will get hungry, you will be tempted, and you may even question why you are fasting at all. However, research has shown that a positive mindset can help you persevere through these types of challenges (and it’s also good for your overall health!). 

When negative thoughts start creeping in, reframe your thinking. Choose “my body has the ability to tap into its own fat stores” instead of “I hate it when my stomach growls,” or “by ending my eating window now, I’m setting myself up for better sleep” instead of “I really wish I could eat my late-night snack right now.”

Takeaway: Have a plan of action and maintain a positive outlook.

Have a Plan to Track Your Fast

Tracking is an important tool for creating a habit. Tracking engenders accountability, helps reinforce consistency with a new behavior, and creates a reward system. Zero has tools such as the Timer and Habit Tracker that offer a great way to log your fasts and track your healthy habits!

Takeaway: Make tracking a consistent part of your daily schedule to form a fasting habit for life.

Ready to start using Zero? Take the quiz or download the app today.

Nicole Grant, RD
Posted in Health & Science


  • What about Chai Tea? I have been told that the Arkadia Chai has zero caffeine so i wondered if this is a good replacement of hot beverages?

      • Lol. Yea chai has its own distinct desi flavor though, so Chai is now recognized as that unique desi flavor. No one will call green tea “green chai” although it linguistically is correct

    • That depends on a lot of factors and what your goal is! An example: I want to lose fat at a weight of 167lbs. I eat 1800 calories. My friend who is 180 lbs. want to gain muscle and is eating 3000 calories.

  • I’ve done the 20:4 for three days. I’m trying to loose weight is it ok to come of it and go to the 13:11 for one or two days

    • Yes, you will have to mix it up with different types of feasting and fasting. Otherwise your body will adapt and you may not be able to lose weight.

    • Sure. You can do the longer fasts a couple of days per week. No problem. Just be careful with calories intake. Don’t overeat.

      • Does anyone know when the fast officially starts?my last meal was 7 pm Saturday night and I set my fast clock 4am the next morning,is it in fact after last meal?Any help …

  • I’m a fairly busy individual with 2 jobs and little to no time to cook. I’ve been relying on prepackaged salads, hard boiled eggs, and a lite dressing as my meal for work. Do you have any other simple, no prep suggestions?

    • Why not just meal prep, you could make your own salads with your protein do choice and keep them ready to go in the fridge! Also overnight oatmeal if you eat breakfast. For dinner you could have prefrozen ziplock bags with veggies and meat already seasoned and then you could just dump them in a pressure cooker like the instant pot. It’s definitely worth trying

  • Wait – no caffeine during the fast? I see clean fasts that include black coffee and green tea??? Please explain

  • Do the following breat a fast:
    1) Bulletproof (butter, MCT oil) coffee
    2) lemon-ginger, turmeric water
    3) kombucha tea

  • I am a 6 year post Rny gastric bypass patient I am trying to lose another 30-50 lbs. I have to eat late at night right before bed in order to take my medication or my stomach gets very upset and hurts like hell. I can go all day without eating just drinking tea and water, but I get hungry in the evenings. What hours should I be fasting?

    • I’m exactly the same as you and insure when to fast I click it at 4am and fast for 13 hours but in my eating hours I tend to eat muslie jacket potatoes with tuna and salad.

  • Regarding my morning coffee. Drinking it black is rough! Ive read that you can technically have creamer as long as you are under 50 calories and this wouldn’t necessarily break the fast. Thoughts?

  • Hi, I just start with fasting and I wanted to ask about fasting 5: 2 diet: With these methods, you consume only 500–600 calories on two non-consecutive days of the week, but eat normally the other 5 days.?Or I was tinking maybe to start with 13:11, it may be the easiest?

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