Prolonged Water Fasting For Weight Loss: Is It Safe?

Fasting is not a new concept; we’ve been practicing this for years in various ways. For example, people are required to not eat in preparation for blood tests, surgeries, and other medical examinations. However, last 2012, a BBC documentary by Dr. Michael Mosley, entitled “Eat, Fast, & Live Longer,” was released and it led to the booming recognition of intermittent fasting (IF) as a means to lose weight. As IF became popular, so did prolonged or extended fasting, which was explored by a lot of doctors and scientists for its mechanisms and benefits.

I know that people are reluctant to try it because it has been dubbed by some as “starving yourself to death,” which is NOT the case at all. This view of many on the practice propagates fear and feeds the connotation that fasting is unhealthy, resulting only in weight loss and nothing more. These are all myths! The fact that it is being practiced for years by both men and women, obese and lean people alike, should be an indicator of how safe and beneficial it can be in the right circumstances (there are exceptions).

Yes, the idea of not eating for a whole day can be pretty intimidating. However, everything that’s unfamiliar is usually scary at first. You’re not well-versed on the topic yet, which is the reason why you may have doubts. That is why learning about how it works and its benefits is important; it erases the lingering fears and misconceptions about the matter.

Let’s talk about some of the questions that people have, including its safety.

IF and Prolonged: Are they different?

By definition, the adjective ‘intermittent’ means that something is occurring at an irregular interval. On the other hand, ‘prolonged’ means that the duration of a certain act is extended. So, yes, IF and prolonged fasting are different, but both involve not consuming food for a certain period of time.


For IF, timing, having a proper meal plan, and a healthy lifestyle are the keys to success. There are three types of IF and these differ in the time interval in between meals.

  • Time-restricted feeding | Daily approach – This IF approach involves eating 2-3 meals daily, but only during a certain time window. For the 16/8 approach, you have to schedule your meals within an 8-hour time frame and go fasting for 16 hours. For example, you will fit all three of your meals within the time window of 7 am to 3 pm every day, or you may simply be limiting the number of meals you’re having all together. And for the 12/12 approach, you have to fit your meal schedule within a 12-hour time frame, such as 7AM-7PM. Most people who are gently introducing themselves to fasting prefer this approach because it’s easier for them. However, the extent at which ghrelin level is lowered using this approach is not as great as the others approaches, and you will see faster weight loss results when you are further limiting your eating window.
  • Whole-day fasting | 5:2 approach – This involves eating regularly for five days a week, and then using some level of fasting for the remaining two days (for example, on Wednesdays and Saturdays). During non-eating days, only one meal is consumed, which must only provide 25% of the body’s daily calorie needs, thereby putting you in a significant caloric deficit.
  • ADF – This is an approach of IF where you alternate between days of no eating at all and no food restriction, more or less. Compared to the first two approaches, ADF shows an even greater effect on lowering ghrelin levels and increasing leptin. ADF works by having “non-eating” and “eating” days. For example, during TThSatSun, you won’t have any food restrictions and eat healthy meals thrice a day, or the number of times that you want to eat. But during MWF, you’ll either fast entirely (no food at all), which is the strictest form of ADF, or you can eat one meal that gives you only 25% of your daily calorie needs. Fasting completely during non-eating days is the most effective approach among all IF methods as it is highly unlikely that you won’t go into a caloric deficit.


A great number of studies have been showing the benefits of IF or ADF to a person’s health, especially when it comes to decreasing the risk of various diseases and regulating insulin levels. To summarize, here’s a bulleted list of some of the many studies I’ve been able to find:

  • According to Dr. Monique Tello from Harvard, it can lead to weight loss through reduced insulin levels, and it reduces the risk of obesity, diabetes, and high blood pressure. In the article, the following information was mentioned:
    • Between meals, insulin levels remain low as long as you don’t snack. During this time, fat cells release stored sugar instead to use up as energy. As long as you keep your insulin levels low by not snacking in between meals, your body will burn fat and you’ll lose weight.
    • Since IF involves meals that are fit into an eight-hour period during the day, it syncs up to our daytime metabolism and prevents us from eating at night. Eating at night has been proven to increase the risk of obesity and diabetes.
    • Lastly, Dr. Tello mentioned this study wherein a group of obese men with prediabetes showed improved insulin sensitivity, significant drop in insulin levelslowered blood pressure, and a significant decrease in appetite after five weeks of IF.
  • Dr. Jason Fung, who wrote the notable books on the topic, as well as obesity, entitled “Obesity Code” and “The Diabetes Code,” discussed how it can reverse Type 2 Diabetes by regulating and lowering the blood glucose level, alongside lowering blood pressure and aiding to weight loss, too. Type 2 diabetes is known to be chronic, progressive, and incurable.
    • One success story was Dan Shadoin’s. Suffering from type 2 diabetes, he was advised by his doctor to go on insulin when his diabetes progressed further. In order to try and avoid the need for insulin medications, he started doing it and went on a low-carb diet. After four months, he lost 68 pounds and his blood sugar and pressure levels stayed low and stable.
  • Fasting is ketogenic, and as the fats are used up and ketones are increased as its product, it suppresses appetite despite weight loss.
  • systematic review of 40 studies stated that IF resulted in weight loss of 7-11 pounds over the course of 10 weeks.
  • It can cause immune response in our bodies that will repair cells and produce positive metabolic changes that will improve both overall health and tolerance to metabolic stresses and diseases, as discussed in this review and this systematic review – which is called autophagy.
  • In this study, the researchers revealed that IF increases stress resistance, increased life longevity, and decreased risk of disease, such as cancer and obesity. Furthermore, IF led to fat loss while maintaining muscle mass, resulting in a leaner body.


Most people already think that ADF is too extreme. Then what would you think about prolonged fasting, which involves only water and no food for 48 hours and longer? Those people will definitely it’s crazy, I know. But here’s the thing: it’s not crazy at all. It’s doable (I, for one, sure succeeded in it) and scientifically proven to be beneficial in more ways than one.

Long-term fasting typically involves water fasting, wherein the individual only drinks water and does not consume any calories. Some people may do it in different ways, such as with juice or bone broth, but these aren’t really considered truly as fasting because they would still be consuming calories from the juice or broth. So, moving forward, I’ll only be discussing prolonged water fasting, which is what I personally tried.

Essentially, it is a way to let your body to stay in ketosis for an extended time. Ketosis is when your body solely breaks down fats as a source of energy because there is no glucose (food intake) available. So, you’re not really starving yourself, per se, because there are stored fats in your body to act as an energy source. Some people can even go through 21 days of zero calories, although it requires you have a certain level of body fat. I’ve personally gone more 14 days of no eating and achieved great results which you can check out.

Through ketosis, your body will shed off fat effectively, on an average loss of 1-2 pound/s per day, and this is just the tip of the benefits long-term fasting can offer.


If meal timing is the pillar of IF, for prolonged fasting, it’s important to be disciplined and keep yourself hydrated. Afterwards, it’s important to consume only the appropriate food: low-carb, high-protein, and low-sugar if you still want to continue losing additional weight.

  • The extent of how much prolonged periods helps weight loss has been studied by numerous scientists. This study has shown that if done for multiple days, it decreases ghrelin despite not consuming food.
    • Men and women underwent it for three days, and it was found out that their ghrelin levels decreased gradually throughout.
    • They also found out that after extended periods of time with no food, the patients turned out to feel less hungry, a stark contrast to what they expected. It turned out that their hunger disappeared, and their appetite are easier to sate, thus they eat LESS and feel full EASIER compared to the time when they were in fact eating.
    • This is because there was a significant decrease in ghrelin, which turned off certain food cravings, especially in women.
  • Fasting is ketogenic, and as the fats are used up and ketones are increased as its product, it suppresses appetite despite weight loss.
    • Ketones are also known to starve tumor and cancer cells, since these cells are glucose-dependent. In this study, evidence has been found that the ketogenic diet can selectively starve tumor and cancer cells. Since normal cells in our body can use ketones while a lot of cancers and tumor cells cannot, the ketogenic diet is suggested to be safe to include in the treatment of cancer.
  • Antioxidant levels in our bodies go up during fasting, which is a good thing because these repair damages and help our bodies fight off infections. Some examples of antioxidants that go up are zinc and uric acid, which both stabilize and do not peak to dangerous levels.
  • Autophagy happens during, as well, which is a condition wherein your body self-cleans via recycling old, damaged proteins, microbes, and mitochondria to build new tissues.
  • An increase in human growth hormone (HGH) levels happens during prolonged fasting. HGH promotes growth and muscle strength, and improves weight loss and metabolism.
    • In this study, 11 adults went 24 hour with no food, which resulted in higher HGH levels.
    • Also, this study involved nine men who went on a 48-hour fast and this resulted to a five-fold increase in HGH production rate.
  • Prolonged fasting can curb unhealthy eating habits and can offer emotional and psychological benefits that IF cannot provide. It forces you to find other ways to deal with emotional or stress-eating.
    • During IF and KD, some people turn to stress-eating of ketogenic or healthy foods when faced with stressful situations or mood swings, which doesn’t actually help in breaking them out of their unhealthy eating habits (stress-eating).
    • With prolonged fasting, if you manage to stick until the end, you’ll see that your eating habits will improve, just like how this success story reported a better relationship with food afterwards as well. It is the easiest way to break your cravings for those unhealthy foods you just seem unable to stay away from!

How to get started

No matter what you do in life, trying out something new is usually accompanied by some degree of struggle at first, but it will get better. Riding a bike, swimming, dancing, sewing, cooking—learning all of these takes effort, and you’re bound to face some challenges at first. So, it’s best to start off slow and read guides and studies so you have a good grasp on what you’re doing.

Consult with your doctor

First and foremost, you have to ensure that your body doesn’t have any underlying issues that can interfere with fasting. There are certain things that may make you ineligible to do it, however, you always need to start off by consulting a doctor.

  • People with severe diabetes and other chronic diseases may not benefit from the practice. ADF can indeed reverse type 2 diabetes but people that have severe cases of diabetes or are already taking insulin shots and under other medications should make sure that these medications don’t mean they won’t be able to fast. If you’re on any of these medications, an alternative may be to start out with the ketogenic diet instead.
  • Pregnant or breastfeeding women must have a well-balanced meal to support the growth of the baby and lactation.
  • The elderly usually have various medications that requires them to eat regularly, and have underlying diseases that can make it life-threatening for them.
  • Young children and teens are still rapidly growing. Their bodies need a high intake of nutrients to support their growth spurt and help their bodies adapt to puberty changes.
  • People who have prior or existing eating disorder should steer away from it. This practice may morph into a form of abuse or punishment for them. Also, it can trigger a “fasting high” that is usually associated with eating disorders, which causes the patient to become obsessed.
  • If you don’t have the necessary amount of fat to sustain no calories coming in, do not even try – I have previously added weight to be able to do a longer fast. While you may not be putting food in your body throughout this process, you will still be getting your energy from somewhere – your fat stores.

Choose which type is right for you

In my opinion, ADF is a good place to start before you move on to prolonged fasting. However, you should adjust it based on the type of lifestyle and amount of physical activity that you do daily. Also, if you ever get sick, like catching a cold or flu, you should adjust your food intake according to what is right for your medications. I have previously broken a fast earlier than I intended on doing because I didn’t feel optimal.

You’re the one who’s in tune with your own body—listen to it. Once you’re confident that you can handle more, feel free to consider it and the benefits that it offers. It’s the most effective way that allows you to shed off fat, as well as doing it at a pace you probably wouldn’t believe possible. In just two weeks, I was already able to lose a lot of fat and my double chin is nowhere to be seen! The appearance of my face vastly improved!

Start slow and adjust according to your health’s state

If you want to get on prolonged fasting right away, it’s okay! However, do not attempt to start immediately with a 21 day one or longer. Ease yourself into it carefully by starting with a 24-hr one for the first week or so. Next, try to increase it to 72 hours. Once you feel more comfortable with the feeling, you can go on and try 10 days or longer.

Make sure that you’re tracking your mood and potential unwanted side-effects on your body. Every person is different, and taking note of your body’s response is important so you can adjust your schedule and meal plan according to what your body needs.

If you feel any severe dizzy spells or sickness, consult your doctor immediately, and start eating food again. You might have some underlying illness that you weren’t aware of, and it’s important to address it first.

Hydrate and take multivitamins during prolonged fasting & Eat balanced meals during ADF

Unlike in ADF where you’re still giving your body some sources of nutrients, albeit at a certain time interval, in prolonged fasting, you need to supplement yourself with the vitamins and electrolytes that it needs. Remember, we’re only trying to deplete the carbohydrate/sugar reserves in our bodies when we fast, so that our bodies will switch to ketogenesis and the breakdown of fat reserves will occur.

We’re not trying to take away everything from our body. Staying hydrated and drinking multivitamins are important. If you want to drink something other than water, you can go ahead and drink green tea or electrolyte drinks but make sure that these are not sweetened.

For ADF, as a general rule of thumb, this is the ratio for a well-balanced meal on a plate, dubbed by Harvard’s The Nutrition Source as the “Healthy Eating Plate”:

  • ½ of your plate must contain of vegetables and fruits (except potatoes!)
  • ¼ of your plate must contain whole grains (think whole wheat, barley, oats, and brown rice)
  • ¼ of your plate must contain healthy protein (fish, poultry, beans, and nuts; limit red meat to minimum)

Just like in prolonged fasting, hydration is important in ADF, too. Drink plenty of fluids daily, preferably water, tea, or coffee (if you can handle your tea and coffee with no sugar, go for it). Limit dairy drinks to 1-2 servings only every day, and avoid sweetened drinks as much as possible. On days of not eating, however, you cannot have anything that contains calories.

Keep your exercises mild and keep yourself occupied

Since your body will be breaking down fat reserves and you’re consuming fewer (ADF) calories or none at all (prolonged fasting), it’s important to be careful exhausting yourself with heavy workouts and cardio, especially if you’re new to fasting.

My suggestion is to take walks rather than running or jogging, do mild yoga instead of cardio, and try to meditate when you feel restless. And if you’re bored, it can be easy to fall into the temptation of snacking on some food. Distract yourself by indulging in your hobbies, or go and look for new exciting activities that you haven’t had the chance to try.

When you initially start, you will realize just how much time you have previously been spending eating.

Track your progress

It’s easy to lose motivation when you don’t have the right support backing you up and when you’re not aware of just how great you’re doing. When checking for your progress, don’t just use the scale. Take photos for visual progress, take note of your body stats with a tape measure, and use a tracking app to make your calorie count easier. It’s always rewarding to know that you’ve made progress, and this will further encourage you to persevere until you reach your goal.

Break it correctly and slowly

For prolonged fasting, it’s very important to reintroduce the right type and amount of food slowly into your system when breaking it. Your body might go into a shock, causing heart failure, hypotension, and other fatal consequences if you suddenly binge eat after a long duration of fasting. After getting used to ketosis, suddenly getting an influx of carbohydrates will cause a flood of insulin in your body. This process requires other necessary vitamins and minerals, which your body do not have in abundance since you’ve been fasting.

Basically, you must start with a small, light meal. Increase the amount of food slowly, adding only small increments per day or per week. To break it properly and avoid complications, you should study this guideline:

  • To break one that lasted longer than 15 days, start with 5 calories/kg of body weight, otherwise, start with 10 calories/kg of body weight. Increase the amount of calorie intake daily by 5 calories/kg only.
  • Drink a supplement with B-vitamins, thiamine, phosphorus, potassium, magnesium, and sodium a few hours prior to eating.
  • Eat slowly and carefully, taking small bites and sips to avoid upsetting your stomach.
  • Try to break it with bone broth or unsweetened/diluted fruit juices first before eating solid foods. Start with soft solid foods first, such as pureed vegetables.

Remember to always listen to your body. If something does not feel right, make sure to check with your doctor right away. Practicing fasting safely is what’s important.

Leave a Comment

Your email address will not be published. Required fields are marked *