Multi-Day Fasting – A Guide

Energy can be stored in various forms


A multi-day fast is an incredible experience for excellent long-term health but unfortunately viewed as impossible by most people. Read now about how you can joyfully make it happen well for yourself.

For ease of navigation, to allow you to jump to the parts that interest you, here is a hyperlinked content list.



Quick Thanks
Quick Disclaimer
A Quick Definition of MDFx
Which x? Why MDF5, not MDF3?
Calories, calories, calories
Multi-Day Fasting (MDFx) vs Time Optimized Feeding (TOF)
Strict Warnings
Warning – Money and Power
Light Warnings
The Science and Benefits of MDFx
My Articles on Fasting
Scientific Studies
O B S T A C L E S   &   M O T I V A T I O N
When to do it
Gender Differences
Dealing with Hunger
Initial Motivation
Broad Philosophy and Deeper Motivation
Keeping yourself Motivated
Downside of MDFx
Abort Mission
MDFx for the Sick
MDFx if you are a Type-2 Diabetic
Periods, Pregnancy, Infertility and Menopause
Medication on the MDFx
MDFx and Chemotherapy
Biomarkers to Track
Ketone Kompetition
Blood Pressure
Body Temperature
N U T R I E N T S  *  R E S T  *  A C T I V I T Y
Preparation (before)
Exercise Just Before
The Meal Just Before
The Extra Time
Rest, Recovery, Sleep
Fasting Mimicking Diets
Water and Salt – Caution
Stimulants – Caffeine
Stimulants – Nicotine
Weight Loss and Fat Loss
Muscle Loss
Cooking and Meals for Others
The Feast After the Fast
Mental Activity
Thoughts about Food
Irritability and Anger
Other People – Famly, Friends, Colleagues
Socializing – Drinks and Dinners
Thoughts after the MDFx
F U N    &    F. A. Q. s
Fun Experiential Facts about MDFx
FAQ – Is an MDFx hard?
FAQ – Does it get easier?
FAQ – How often should I do an MDF5?
FAQ – Should I do an MDFx for fat loss?
FAQ – Where do I sign up for an MDFx? What about the medal, certificate, and t-shirt?
FAQ – Won’t I just become fat again when I start eating after MDFx?
FAQ – Is there a benefit to an MDFx if it makes me feel weak and I end up spending large parts of it in bed?

The Path Ahead
For you


Quick Thanks [top]

I appreciate the contribution of topics, sub-topics, FAQs, ideas, and thoughts from friends, mentees, and others around the world that has enabled me to cover a wide range of practical issues beyond just my own direct experience.


Quick Disclaimer [top]

Regardless of the Quick Thanks, I would like to state that the opinions that I have expressed throughout this article are mine and not to be linked to anyone else I might be associated with for any of the varied projects I work on.

If you do not agree with something I say, please write to me at I would love to hear from you!


A Quick Definition of MDFx [top]

MDFx is Multi-Day Fasting for x days.

The MD of MDFx for multiple days can be for anything equal to or more than 48 hours, so 2 full days or more.

The x of MDFx represents the number of days e.g. I did my first MDF5, a 5-day water-only fast in March 2018.

The F of MDFx represents ‘fasting’ e.g. for my first MDF5, water was the only nutrient that I consumed. There are variations of it that might be equally good or even better, in certain cases. I describe one approach in the section on Fasting Mimicking Diets.


Which x? Why MDF5, not MDF3? [top]

The studies so far, on mice, have concluded that when translated to humans, for humans to get the benefit of a prolonged fast, the minimum period is 4 days, or perhaps even 5. It is for that reason I pick an x = 5 to be reasonably sure of achieving the benefits. If for some reason you want to do an MDF8 e.g. for the Jain festival of Paryushan, you should!

An MDF2 or MDF3 will also be beneficial, but not as beneficial as an MDF5. If the alternative is to do nothing, definitely pick an MDF2 over nothing. You can do an MDF2 quite often. Perhaps even every 2 weeks, so perhaps twice a month. See the FAQ – How often should I do an MDF5?


Calories, calories, calories [top]

Calories is a concept and measure of energy from physics that does not translate very well to either human biology or healthy weight management. I use it here, relatively loosely, to refer to fuel through food intake. I discourage and do not recommend calorie-counting food as a focal point for your optimal health.

In case you are puzzled by what I just said, ask yourself – “what happens to my body fat from eating an entire bar of chocolate 24 hours before the end of my MDF5 versus eating the same bar of chocolate 1 hour after the big meal at the end of my MDF5?”

If you understand the answer to that question, you will never primarily worry about the calorie number of a food item.


Multi-Day Fasting (MDFx) vs Time Optimized Feeding (TOF) [top]

If you are someone who does sensible Time Optimized Feeding daily, then you will know that the daily fasting is not about calorie restriction – it is only the timing of the total daily food and drinks intake that is optimized. On the other hand, with MDFx, the total calories you will consume during the x days will be zero! So, unlike with TOF, you will end up severely restricting calories and nutrients – at least during the x days.

See Fasting vs Calorie-Restriction


Strict Warnings [top]

Do NOT consult your doctor before attempting this if you are generally in good health, as they are unlikely to give you the best advice on this topic and may tempt you away from it. Conventional medical doctors typically go through medical school being [1] taught that you need to eat every few hours and [2] not being taught anything about food. In time, despite your typical medical doctor not having mal intent, that approach to teaching in medical schools has only created more sick people on this planet! There is a significant gap between published scientific research and advances in human biology and what your typical physician practices. Don’t hurt yourself when you fall into that significant gap. If your physician is the rare case of someone who understands MDFx and has practiced it, great! Use them to your advantage!

Do NOT attempt to do this if you are a minor.

Do NOT attempt to do this if you are pregnant or are breastfeeding. If you are trying to conceive but are unable to because you are overweight and wish to use MDFx as part of the host of lifestyle protocols you are keen to try before (or alongside) ART, then do so.

Do NOT attempt to do this if you have been diagnosed with any mental health disorders regarding food e.g. anorexia nervosa.


Warning – Money and Power [top]

A whole generation of medical specialists (e.g. diabetologists) and pharmaceutical products (e.g. hypoglycemics) could become extinct within a decade if everyone implemented TOF and the occasional MDFx in their life. And it does not stop with Type-2 Diabetes. With better insulin sensitivity in the first 7 decades of your life, you could reduce (I did not say eliminate) the risk of Alzheimer’s in the subsequent 3 decades of your life, to reach 100. If you are worried about cancer or heart disease and did not have to worry anymore, think about who would be worried!

My friends who own pharmaceutical businesses implement TOF and MDFx to reduce their own need for medication. They would love it if you had good health and needed their products to be mostly about formulations to enhance your Healthspan rather than to keep you free of self-imposed aches and pains from the lifestyle choices you make. Use the power within you to not put money into deep pockets for wrong reasons!


Light Warnings [top]

If you operate dangerous or critical equipment (e.g. you are piloting a Boeing 747 or a chainsaw for woodcutting) please approach MDFx in progressive steps. Start with TOF, then try MDF2, MDF3, and so on.

Stay away from people who think that fasting, other than when one is asleep, is something extreme. But if they annoy you, be prepared – read Irritability and Anger.

If you have a friend who is experienced and knowledgeable about MDFx you may want to stay in touch with them during your first MDFx. If they are a healthcare professional, even better.


The Science and Benefits of MDFx [top]

This is a “guide” or “how to do it” and so I am specifically not including a section on “why”. You could check out the published literature or popular videos on MDFx (search for “prolonged fasting”). Read what I say here on Scientific Studies as applied to longevity. And, read My Articles on Fasting.

Despite not having a section on “why”, you will notice as you continue to read through this article that I have sprinkled various benefits of MDFx throughout in various sections. Not just for physical health, but mental, emotional and spiritual too.


My Articles on Fasting [top]

In chronological order, including articles published after this one:

Why does the son of a Hindu Brahmin fast during the Muslim month of Ramadhaan?
Time Optimized Feeding – Your Easy Guide to Fasting
Ramadhaan Running for All Faiths
Time Optimized Feeding – 2 Years of Daily Fasts
Ekahari and the Birth of the Brunchnner
The Ekahari Log Blog
Multi-Day Fasting – A Guide [this article]
MDF5 – The Log Blog


Scientific Studies [top]

Based on human subjects there are currently many short-horizon studies on both fasting (timing of calories) and calorie restriction (not about timing). The benefits of both are no longer a matter of opinion.

There are numerous mechanistic studies on smaller animals (mice, in particular) and the benefits of fasting and calorie restriction on the quality of their lives and the length of their lifespans. Systematic longevity studies can be done on these animals because of their naturally shorter lifespans e.g. from a few days (worms) to 2-3 years for mice. To the extent that the learnings transfer to humans, there are immense benefits.

There are no long-term studies on longevity and the impact of prolonged water-only fasting in humans. There are only specific case studies, anecdotes and stories one can find about prolonged fasting.

There are hundreds of thousands of humans who do an MDFx at least once a year for many hundreds of years. This is for religious reasons. Because of wrongly held beliefs that one should not be pricked for blood samples during religious fasts, those engaging in MDFx as part of their religious beliefs are typically unwilling to be part of even short-horizon prospective cohort studies. When that mindset changes, and we can collect data on humans, we will be able to tease out more definite answers on the impact of MDFx on short-horizon benefits (soon) and on Healthspans of humans (after 100 years?).

For now, it is best to piece the puzzle together based on studies contributing different pieces e.g. lab experiments on cells and tissues, studies on small animals with much shorter lifespans than humans, epidemiological studies, studies of centenarians, and prospective cohort studies on human patients signed up for studying short-horizon benefits.


When to do it [top]

Although you do not require specific or special experience with fasting, if you have been living a healthy life with 12-hours overnight fasting as standard, it might help to have done a few 24-hour fasts. You may want to seek a period when
[a] most people you share the home with are away
[b] there are no party attendances planned
[c] there is no travel planned
[d] your workload in the office is not particularly high
[e] there is no critical deadline for any project.

If you want better mental preparation, it would be good to have started with regular Time Optimized Feeding. Do keep track of increasing duration overnight fasts, and give yourself the confidence that you can do without food for long periods of time. Note again, it is not necessary to have any prior experience.

I had been focusing on Time Optimized Feeding for 797 days before I did my first MDF5. On the other hand, a Chinese brother from Malaysia who lives in Hong Kong pleasantly surprised me with news of his MDF5 with no prior experience of fasting. He did it when his wife and daughters were away for a few days.

See Socializing – Drinks and Dinners


Gender Differences [top]

In general, men should not have a problem with an MDFx. Although many females manage to go through it smoothly, some face a tough time, driven primarily by strong responses by the endocrine, nervous and neuroendocrine systems. If you cannot lie down for 20 minutes to allow ‘a crazy phase’ to pass, then go ahead and break your fast. Just eat something sensible and relax. Aborting is OK. You can always try again after a few weeks. I will say it once again; hunger is not a reason to worry about MDFx or to abort it. See Abort Mission

The flip side with gender is that females are naturally better at enduring pain. Bear that in mind to motivate yourself and carry yourself through your MDFx.

See Periods, Pregnancy, Infertility and Menopause


Dealing with Hunger [top]

If you speak to anyone who has done an MDFx they will confirm to you that after 2 days (some cases) or after 3 days (all remaining cases) there is no further feeling of hunger. Imagine that, no feeling of hunger on day-4. No feeling of hunger on day-5!

That leads to 3 useful guiding principles:

[1] You can be in a state of ‘no hunger’ after some days, something that you will have never experienced – worth doing just for that? How empowering will that feel!!
[2] The ‘hunger annoyance’ is the same, and at the start only, for an MDF2, MDF3, MDF4 and MDF5
[3] So, if you settle for an MDF2 or MDF3, you get all the downside ‘hunger annoyance’ without the significant incremental upside of an MDF5. Try to not miss out on the benefits of an MDF5 if you are going through the ‘hunger annoyance’ at the start of an MDF2, MDF3, MDF4 or MD5

Even in the first couple of days, the hunger pangs themselves come in a pulsatile fashion over time – a feeling of hunger that appears to be in the stomach is actually a sensation produced by the brain and never stays with you for more than a few minutes at a time. So, hunger is not like a headache that just won’t go unless dealt with. If you show patience through those few minutes of hunger and do nothing, the hunger sensation will disappear.

Healthy humans do not get a headache as a message for hunger – the hunger sensation in itself is different from a headache – after all, all humans do not get a headache every time they are hungry, and every headache has not implied hunger. See the section on Headaches below.


Initial Motivation [top]

As one of many longevity protocols that I implement in my life, I had been fasting for many years, but never for more than a day. The additional benefits that accrue to humans from a water-only-fast that goes up to a minimum of 4-to-5 days, is what motivated me. The fat loss from MDF5 will be non-trivial but it will not be large either. My motivation was to increase autophagy, increase stem cell production, and, generally, reset the entire immune system through a regenerative program that is deeply encoded into our DNA.

It may be that your motivation comes from your religious faith (e.g. Jainism recommends 8 or 10 days of water-only fasting during Paryushan). It may be that you have cancer and don’t feel confident about a cure through only chemotherapy and want to increase your chances of success by combining it with fasting. Whether your faith recommends it for your well-being or a scientist does (see MDFx and Chemotherapy) does not matter. As with prayer or exercise, the benefits accrue to you if you do it.


Broad Philosophy and Deeper Motivation [top]

We are often looking “to do” something towards a goal. Whether it is for health or wealth, our focus typically tends towards action, inclusion, investing. With MDFx the journey is about not doing. With time being the most valuable resource that you have, the beauty of an MDFx is that time is saved! The investment is passive, the returns can be massive. It troubles me when I see friends participating in a recreational ultra-distance running event on a single Sunday for longer than I invest in an entire month of exercise. Perhaps an MDFx is something that might benefit society more (give your food of x days away to a needy person) than running 250 laps of a stadium?

You may have heard me rant about how Balance is True Mastery or why I don’t care about your Ultra. Although an MDFx will sound extreme, it is something that anyone can do, with almost no special training. Whereas running 50 miles gives no real benefit (and perhaps is worse) compared to running 25 miles, an MDFx every few months, or once a year, brings real benefits. Please note that doing it too often if x > 2 is also extreme and should be avoided. See How often should I do an MDF5?

With an MDFx you will journey through spaces (physical, mental, emotional, spiritual) where you have never existed in ever before. You are navigating very directly in the physical dimension (not eating) and have to manage to steer wisely in the mental and emotional dimensions. If all of these 3 are not on a good track, the spiritual dimension will probably not see too much benefit.


Keeping yourself Motivated [top]

Remind yourself of your initial motivation to do MDFx. Having faith in science, in general, and the science behind MDFx is a very powerful motivation tool. If your initial motivation was your religious faith, it is likely your motivation will be even stronger.

You will find hundreds of videos on YouTube that are related to fasting that you can watch spread over the x days.

If there is someone elsewhere in the world that is doing the MDFx at the same time, and you are in touch, you will find that it helps to motivate each other. I don’t need it, but if you do, please use that too when possible.


Downside of MDFx [top]

Like with anything (e.g. even drinking water!) there is a downside even to MDFx. If there wasn’t, you might do it every week – e.g. do MDF6 from Mon to Sat and eat only on Sundays!

For x days you are not ingesting all of the nutrients that your body would normally require, and will work on stored nutrients. You have to bear that fact in mind and hopefully [a] it will make you focus on the nutrient details and nutrient density for the first 4-6 meals after your MDFx and [b] it will encourage you to eat well every day during the rest of the year.


Discipline [top]

Unfortunately, when people think of ‘discipline’ they picture ‘hardship’. For those who are successful at whatever it is that they do, discipline is actually about being systematic and consistent. For them, a life without discipline is perceived as one of hardship – hardship introduced by choice – the choice to not be systematic and consistent.

For your MDFx, discipline mostly revolves around those two features – being consistent and systematic about the process. If you were planning to weigh yourself daily for a week before, during, and a week after your MDFx, then do that. It’s not painful! If you were going to be consistent about weighing yourself at a certain time of the day (e.g. after your morning shower) then do just that. It’s not painful!

Having a plan is essential for success with anything. If you prefer to avoid being around others eating during mealtimes for the first couple of days, then make a plan to do something elsewhere then. Don’t just let life happen to you!

Other than that, the physical, mental and emotional stress you might go through has nothing to do with discipline or self-discipline. Going through that period, knowing that you were seeking that ‘pain’ only improves your level of wisdom. You need to have faith in the science of fasting. Be consistent in reminding yourself of the science behind it.

See Cooking and Meals for Others and Other People – Famly, Friends, Colleagues and Socializing – Drinks and Dinners

Also, see The Accidental Wisdom of Pain Seekers and Discipline – The link between ordinary and exceptional


Abort Mission [top]

Despite all the planning and pre-planning that you do, sometimes things can still go awry in the physical dimension as you enter previously unexplored spaces. The wise thing to do is to be safe, and wait for the phase to pass. However, if your intuition tells you that, beyond reasonable doubt, you should abort to be safe, then abort. If you are robust in the mental and emotional dimensions you will find that you can withstand any ‘crazy phase’ that might suddenly appear (typically near the end of day-2, primarily for females). See Broad Philosophy and Deeper Motivation

Oh, one bit of seriously scientific advice – feeling hungry is not a valid reason to abort!


MDFx for the Sick [top]

The science I follow through the scientists whose work I track leads me to believe that for a vast number of illnesses, rather than staying away from MDFx, implementing it would actually be beneficial. Once again, two bits of advice [1] safety first [2] follow the science rigorously. Hold yourself responsible.


MDFx if you are a Type-2 Diabetic [top]

If you take medication as a type-2 diabetic instead of curing the problem (e.g. through a scientific approach to fasting) and would like to do an MDFx, please make sure that you do not take any medication that lowers your blood sugar (e.g. metformin) during the MDFx. See MDFx for the Sick.


Periods, Pregnancy, Infertility and Menopause [top]

It is best to avoid MDFx when you are having your periods unless you think you will enjoy the dual experience.

If you have been diagnosed with infertility related to metabolic conditions (e.g. Type-2 diabetes, PCOS) and want to get your health back in order, use the MDFx as part of the many lifestyle protocols that will help you to conceive naturally, or prior to investing in ART (e.g. IUI, ICSI, IVF).

Avoid it during the ovulation phase of your menstrual cycle if you are trying to get pregnant that month. Don’t forget the folic acid in this phase of your life.

If you are pregnant, do not do MDFx. See Strict Warnings.

If you are going through menopause and find hot flushes a bother, your experience may go either way. You may enjoy feeling colder (see Body Temperature) or you might be extra frustrated on day-2 and day-3.


Medication on the MDFx [top]

Most medication has higher potency when you are fasting. If you happen to be taking any during the MDFx, please be aware of this phenomenon.


MDFx and Chemotherapy [top]

If you have been convinced that your only cure for your state of cancer is chemotherapy then, besides reading this, you should consider integrating it with MDFx. If MDFx appears unmanageable then see Fasting Mimicking Diets. I strongly recommend that you spend some time here. It may be that FMDs are better for you than MDFx during chemotherapy. You should also beware that your oncologist may be unaware of the benefits of combining chemotherapy with fasting. See Strict Warnings.


Biomarkers to Track [top]

There are a number of biomarkers you could keep track of through life. In many countries, it should be possible to keep track of the following ones specifically during the period of an MDFx.

  • Weight (Kg)
  • Blood Pressure and Heart (Pulse) Rate
  • Blood (Plasma) Glucose
  • Blood (Serum) Insulin
  • Blood (Serum) Ketones
  • Urine Glucose
  • Urine Ketones
  • Body Temperature

It makes sense to have a digital weighing scale of reliable quality at all times at home and record your weight regularly throughout the year.

It also makes sense to keep track of your blood pressure with a good quality blood pressure machine at home on a regular basis. See Blood Pressure

Unless you are diabetic, it does not make sense to have a glucometer for the home to measure your blood glucose. I am told that they lose their accuracy fairly quickly – so if you haven’t replaced yours for 18 months, do so!

You could buy urine ketone and urine glucose strips for the home. Because they are not expensive, it will not matter that you will use only a fraction of the special chemically treated paper strips before they go past their use-by-date.

For blood levels of ketones and insulin, it is best to send a blood sample to a reliable pathology lab. Note that for ketone bodies, it is typically D3-Hydroxybutyrate that will be measured – it forms a good proxy for total ketones in your blood.

Note that the strips for ketones are nowhere close to being as sensitive as the measures from your blood from a pathology lab. So, you may be in ketosis but your urine ketone strips may not show it unless you are in a state of significant (yet safe) ketosis. A reliable pathology lab for checking blood ketones will be more appropriate on day-1 and day-2 than ketone strips. For day-3 onwards you could use both – the urine strips at home and send your blood samples to a reliable pathology lab.


Ketone Kompetition [top]

It is important to note because most people do not realise this – someone whose blood sample shows a lower level of ketones than someone else, may actually be in a deeper state of ketosis than someone whose blood (or urine) shows a higher level of ketones. This is because the former person’s body may be better ‘fat adapted’ and may be using the ketones up more effectively than the person whose body is not. So, what is more relevant is to check your level of ketones over time, rather than comparing with someone else’s levels!

You can read about why I think that comparing with others is pointless – Why I don’t care much about your podium finish or mine.

Focus on your Genetic Potential Fitness.


Blood Pressure [top]

If you have a blood pressure meter at home, take readings 3-4 times daily for x days before your MDFx, 3-4 times for x days after your MDFx, and as many times as you can during your MDFx. Note the Date, Time, Systolic, Diastolic and, if it tells you, your Heart Rate. Make a qualitative note for each reading that adds colour to the quantitative information e.g. 20 mins after salt water.


Body Temperature [top]

From some time approaching the start of day-2, you may start feeling colder than you normally do. This is great if you are in uncomfortably hot weather, you will not find that a problem – you might even enjoy it! You may want to cover up more than usual when you sleep at night.

Hopefully, you have a good quality thermometer at home. I prefer the mercury ones to the electronic ones. As with Blood Pressure, measure your temperature 3-4 times daily for x days before your MDFx, 3-4 times after your MDFx, and as many times as you can during your MDFx. Note the Date, Time, Temperature, and a qualitative note for each reading that adds colour to the quantitative information. e.g. after walking for 20-mins.

If you measure the temperature inside your mouth, make sure that you do not drink or eat anything in the 20 minutes prior to measuring the temperature.


Preparation (before) [top]

This could be the shortest section. Broadly there’s not much to fasting – you just avoid eating!

See – When to do it


Exercise Just Before [top]

You are going to enter ketosis at some point in the first 24 hours of the x days. This means that if you do a long endurance workout prior to the last meal, you will probably enter ketosis a few hours earlier. My guestimate is that you will enter ketosis approximately 8-9 hours earlier if you did 2.5 hours of an endurance workout (e.g. run, cycle, swim) before your last meal and your last meal is not large. Whether or not you should do the half-marathon equivalent workout (think of running, swimming or cycling for 2.5 hours) especially and specifically before your MDFx is then a function of x.

If x > 5 e.g. MDF8, in the big scheme of things, those “quicker hours” do not matter, so don’t stress yourself out about this point. In an MDF8 those initial 8 hours out of 192 hours will not determine the value you derive from the MDF8.

If x = 5 meaning a 5-day water-only-fast, in the big scheme of things, again those “quicker hours” do not matter, so don’t stress yourself out about this point.

If x = 4 e.g. if for some reason you want to do an MDF4 instead of an MDF5, then you should consider doing a half marathon run equivalent and make your last meal a small meal. Why this distinction between MDF4 and MDF5? See Which x? Why MDF5 not MDF3?

If x = 2 or 3 then I would recommend the long workout and a small final meal. There is no compulsion, but it is what I would recommend to myself or to others doing an MDF2 or MDF3.


The Meal Just Before [top]

You are going to be without nutrients for x days. When I know I will be without food for x days, my focus is on ensuring that I have the micronutrients I need for the x days. You should not worry about proteins, carbohydrates, and fat for your final meal, but focus on whether you are getting enough of the micronutrients (vitamins, minerals, salts, phytochemicals) in the many meals leading up to MDFx. Of course, in general, at any time of the year, you should be asking yourself if your micronutrient intake has been appropriate over the previous week.

Just enjoy the last meal while remembering that there is no upside with eating stuff that is effectively poison for you. See This question can save your life?.


The Extra Time [top]

Your eating for the day typically consumes 60-120 minutes of your waking hours. During an MDFx you will have that many minutes multiplied by x to do whatever you wish. Use it wisely. You can always earn more money, you cannot get back lost time!

Think about what you could do with the extra 5 hours, or even 16 hours. What does that translate to in your life?


Rest, Recovery, Sleep [top]

Hopefully, you always listen to your body when it comes to rest. You should not need extra ‘awake rest’ during your MDFx. The beauty of an MDFx when it comes to sleep timing is that you never need to worry about keeping a 3 hours gap between finishing a meal and lying down.

Because your sympathetic nervous system may be on a slight overdrive in the first few days, you may find that you have shorter sleep. That’s OK.

If you are able to enjoy “free rolling sleep” (continuous undisturbed sleep without an alarm clock) then you will be on to a winner.


Fasting Mimicking Diets [top]

Fasting Mimicking Diets or FMDs use a less strict definition of fasting that broadly involves eating small carefully constructed meals over the x-day period. This approach has allowed some people who would not otherwise have wanted to do an MDFx to do a quasi-MDFx i.e. something that is not fasting but attempts to get at least some of the benefits. The meals are carefully designed for individuals with dangerous health conditions who would benefit from doing an MDFx but are too emotionally weak to be willing to. I strongly recommend that you spend some time here if you think you are an emotional weakling about going without food. Before doing that, please see Dealing with Hunger.

As a scientist and an Ekahaari, this area of FMDs interests me a lot. In general, my suggestion is that if you want all the benefits of MDFx (that scientists are only just beginning to understand) then do your first MDFx without resorting to a FMD.

If you do use an FMD in the future, measure your blood biomarkers daily during the x days. Then, perhaps, a few weeks later (if you are severely overweight) or a few months later (if you are at normal weight) you could try a carefully constructed FMD. You must ensure that you measured your blood biomarkers daily during the FMD version of the MDFx too and try to understand how and why the numbers vary.


Water and Salt – Caution [top]

Although dry fasting (without water or other drinks) can be extremely good for health, being appropriately hydrated is very important for good health at other times. During your MDFx too you need to be careful that you drink the appropriate quantity of water to match up with perspiration during exercise. However, some caution is needed here. In the case that you perspire a lot – pushing out salt – you ought to also keep track of your need to consume some salt (dissolve in drinking water) to replace it. Consuming salt will not break your fast. If you become depleted of salt it makes sense to consume a small amount of normal cooking salt immediately to avoid unnecessary moments of hypotension (low blood pressure). The symptoms of hypotension can be alarming for some – and it would be a pity to abort your MDFx attempt for something negative but transient that has a trivial solution. See Blood Pressure,


Stimulants – Caffeine [top]

Although black coffee will not stimulate insulin production and so, by my definition for the MDFx, it does not break the fast, for your MDFx I recommend that you do not take caffeine so as to not interfere with the body’s various processes. The rejuvenation program inside your body that has evolved over millions of years is very sophisticated – let it do its thing. Although there is only a very limited study so far into the beneficial impact of drinking coffee on ketosis, I think that since the purpose is beyond just ketone levels in the blood, you should stay away from caffeine. You could continue to use black coffee, black tea, and green tea during your normal daily Time Optimized Feeding throughout the rest of the year.

See Irritability and Anger


Stimulants – Nicotine [top]

If you smoke, you might be tempted to smoke even more if you cannot handle the physiological (and mental, emotional) stress in the first 1-to-3 days. If you do not wish to use your MDFx to wean yourself off nicotine, be confident that the MDFx will be offsetting some of the terrible effects of your cigarettes. Please give the cigarettes up during some other time. Soon!

See Irritability and Anger


Alcohol [top]

I do not think that you or anyone else should be drinking alcohol. See Alcohol – Did you Believe the Lie?

Alcohol will break your fast. Unfortunately, it will also break many other things inside you. Maybe, slowly. But, surely!


Weight Loss and Fat Loss [top]

You may often hear someone say they lost a few Kg after a few days of fasting. Please translate that into “a second weighing scale measurement after a few days showed a lower number”.

Do not make the mistake of understanding that “she lost F Kg of fat in just x days”. That is almost always mathematically and scientifically impossible.

The weighing scale reading change will be from true fat loss and deceptively not fat loss reasons. Over say x days these changes will be from:

  1. No new food coming in [this will account for a lowering by ~ 0.5Kg]
  2. No (or lower) salt intake leading to a decrease in water retention i.e. an automatic expulsion of water from the body’s tissues [this will account for the bulk of any drop you see but will vary depending on how much salt is expelled vs replaced]
  3. Digested food that is excreted out of your body within 24 hours [though this is equivalent to 1.]
  4. Digested food that is excreted out of your body over periods much longer than 24 hours [perhaps lowering by another ~ 0.5Kg]
  5. Glycogen depleted by end of day-1 that remains depleted [rarely more than 0.5kg] which will be replenished once you consume carbohydrates after your MDFx.
  6. Fat loss associated with your BMR [at most 0.25Kg per day for x days]
  7. Fat loss associated with above normal physical activity
  8. Fat gain associated with lower than normal physical activity

So, assuming you had no change in physical activity (because you did not do much exercise anyway) and you did an MDF5 (x = 5) your actual Fat Loss would be at most 1.25kg from not eating for 5 whole days even though you may observe a 3kg drop in weight.

And that is assuming you kept your physical activity the same. If you dropped your physical activity levels, or lay in bed a lot because you ‘felt weak’ then you would lose even less fat. It will be unusual for you to do more physical activity than usual during your MDFx.

Be very glad that the fat you will have lost will have been mostly the dangerous visceral (e.g. abdominal, belly) and only slightly subcutaneous (just below the skin) fat.

See Exercise and Biomarkers to Track.


Muscle Loss [top]

Whether you fast or you do not fast, your body responds to stimuli – those from the environment and those that you give it consciously – food, drink, exercise, sleep. As part of that, your muscles respond to the stimuli relevant to their function. So, if you have a sedentary lifestyle and if you do not fast and do not use your muscles you will lose muscle mass. If you do not fast, and stop your gym visits, over a fairly short period of time (measured in days not months) your muscles get weaker and reduce in size (and mass).

When you fast for short periods of time e.g. 12 hours you actually create an environment within your body to enhance muscle preservation and growth (e.g. via increased production of human growth hormone). There are studies that show that during an MDFx, your BMR actually goes up, not down, by day-3. If you are totally sedentary, my guess is that you are likely to lose a tiny amount of muscle mass and if you do a little bit of exercise, you will preserve it well. I would not recommend being sedentary, especially if you were not sedentary before your MDFx.

See the section on Exercise Just Before and for Exercise during.


Exercise [top]

My recommendation is that you continue to do the physical exercise you have been used to during your MDFx. Be watchful and tweak down the intensity and/or volume when needed.

You may find that beyond day-3 your intensity (Kg of a dumbbell at the gym; pace of running; speed of cycling; seconds per lap of the pool) needs to be lowered. Remember, during your workout you are looking for hormesis – and so the numerical values e.g. Kg, min/km or km/hr, they do not mean anything in isolation. Lifting a 20kg dumbbell in the context of “day-5 of MDF5” may be equivalent to 30kg for the exact same exercise in a “normal” workout session.

If you do not exercise for some reason, do not think of your MDFx as being a waste. Remind yourself that the primary goal was to allow your body to experience the benefits of getting no nutrients other than water (and maybe salt) for x days. Benefits beyond trivial fat loss.  See Weight Loss and Fat Loss.

Those who do an MDFx for religious reasons are typically advised by their guides to abstain from demanding physical activity. If you think that advice applies to you, please follow it. My suggestion is to understand the reason for all religious advice. If you think you can manage your physical workouts then see the religious guidance for what it is – guidance – just do your workouts, perhaps at a lower intensity and lower total volume.

See Hormesis – Your best friend and The Science and Benefits of MDFx.


Cooking and Meals for Others [top]

I would not specifically stop cooking for others just because I am fasting. I would also not avoid being with them while they were eating a meal. It does not bother me. It would be good if you could develop that ability too. It might happen very quickly, or it might take some time. Enjoy the process of separating your own negative physical and emotional sensations from your positive tasks and duties.

If you are meeting friends for lunch, coffee or drinks, you could always sip on water while they consume insulin spiking dubious consumables.

See Irritability and Anger


The Feast After the Fast [top]

With the fast done, now is the time for its twin – the feast. Just like you were intelligent about the fast, now be intelligent with the feast.

From your mouth to your colon, your body would not have had an input of food for x days. This would have been absolutely fantastic for the organs, tissues, and cells of your digestive system. My suggestion is that you start your feast very gradually, with as much from raw plants as possible. Often people are cautious and will drink water with micronutrients e.g. salt water from boiled lentils. It makes sense to be cautious, so proceed without greed even if you are adventurous by nature.

The greater the diversity of (insoluble) fibre you can take in during the early parts of the feast, the better – for your gut health. Keep any less healthy fun food items for the end of the feast. In general, as for all meals in the year, focus on fun food that is also healthy. See Poison

Avoid caffeine in food (e.g. chocolate) and drinks (e.g. tea, coffee, green tea, Coke) for the first day or so to reduce malabsorption of important micronutrients that you have missed out on during your MDFx.

Avoid heavily processed factory foods that come in packets even if you find it difficult to stay away from them during the rest of the year.

Eat each mouthful of food slowly, chewing carefully, more thoroughly than you normally would.

Do not drink water or any other drinks for 30 minutes before your feast, and for 60 minutes after your feast. If you have something like a soup (or lentil water) at the start of the meal, try to keep a 30-minute gap before you then eat solid food.

For a list of old articles by me on eating/food see this.


Mental Activity [top]

A dry fast (which is not what we’re focusing on with an MDFx) is likely to cause a drop in mental focus because of dehydration and lethargy. With an MDFx there is no dehydration risk, in fact, there is a risk of over-hydration. So if things go according to plan you should not see a drop in mental energy. See Water and Salt – Caution.

It may be that on day-1, day-2, and day-3 you find it difficult to concentrate 100% of the time. Remind yourself that you are not able to concentrate 100% of the time anyway, on any other day of the year. It is just that in this case, there are unexpected pangs of hunger to distract you (as opposed to yet another email notification). You will notice that hunger pangs do not last for more than a few minutes and you are able to continue with your work.

What is a more interesting space to explore for those who do an MDFx is that when one reaches a stage (on day-4 for most people, it happens on day-3 for me) where there is zero desire for food and the brain works beautifully from early morning until late night. It might even be the most mentally productive day of the year for you.


Thoughts about Food [top]

It may be that you think about food often, even when you are not hungry. It is good to observe yourself thinking about the food, perhaps about your favourite dishes to be consumed when you eventually finish the MDFx. Let the thoughts come, do not fight them, but let them also go easily. Pay attention to which foods you thought about. Pay attention to whether that list of foods is different whenever you do an MDFx again.

Do not tell yourself to not think about food. Just try to not get emotionally affected by the thoughts.


Headaches [top]

If you feel a headache coming along, my suggestion is to attack it before it makes much progress. Have some salt water, lie down for 15 minutes, allow yourself to slip into a nap if you can.

If you are at the office and a headache is destroying your state of calm – I would be interested to know how you dealt with it while continuing with your MDFx and office tasks. Please write to me at


Irritability and Anger [top]

It is very common for most people to be irritable when they are hungry. You have a choice between 2 paths:
[1] You can respond to irritating situations with annoyance and anger
[2] You can make a very conscious effort to be calm [Top Tip: try silence] and cruise through the irritating situation.

The former is your animal response and has mostly downside. The latter is not easy to do, and you may not always get it right, but has massive upside if you stay committed to master it over the years.

In my opinion, if you spend hours in prayer every week, but cannot stay calm and collected through every bout of hunger, then your prayers are being of very little actual benefit to you! Think of it as a litmus test…

Temple, church, and mosque visits that do not help you remain emotionally immune to hunger when required are wasted visits. I shall say it again – standing in a church makes you no more a Christian than my standing in a garage makes me a car!


Other People – Family, Friends, Colleagues [top]

Other than anyone who might be involved in preparing your meals, there is no specific need to announce to others that you are doing an MDFx. You could if you want to, but there is no real need to. If you do mention it to someone you are with, you will learn a lot about the other person by watching their expression closely and listening to their first set of responses. I find that part quite interesting!


Socializing – Drinks and Dinners [top]

You are likely to be the best judge about how much you ought to socialize where your friends are eating and drinking. You might even surprise yourself with how immune you are to other people eating around you. This may be difficult until day-3, but very easy after that.

See Dealing with Hunger and Thoughts about Food


Journaling [top]

For progress in life, success in anything you pursue, journaling can play a critically important role. With MDFx it is no different. What you document besides the biomarkers, in terms of qualitative information or your thoughts and activities through the day, will vary as the days go by. Do make a point to note your weakest moments, when they happened, what they were about, and what you did to get past those moments.


Thoughts after the MDFx [top]

Depending on how your experience of your first MDFx was your thoughts about doing another one in the future will vary. My advice is that you do not make any decisions regarding (doing or not doing) another one until some length of time has gone by. Once a few days or week have gone by, go back to your initial motivational reasons and decide on your policy regarding a future MDFx. You may decide to do another one for a different combination of reasons.

See Initial Motivation and Broad Philosophy and Deeper Motivation.


Fun Experiential Facts about MDFx [top]

Fact: You will not chew anything for x days. When was the last time that that happened in your life?

Fact: If it is summer or hot weather, while everyone else is feeling hot and bothered, you will feel cool or cold.

Fact: Even though a few days have passed since your last solid meal, your circadian rhythm makes you “go in the morning”, and there is significant output! You might see colours you haven’t seen before – enjoy!

Fact: You hear other people wrongly use the phraseI’m starving” when they’re a bit hungry during the day and it’s been just a few hours since their last meal and you realize how we are often so imprecise in describing our own feelings and sensations. It makes you focus even more on the precision of your own spoken and written words.

Fact: You realize once you are past day-3 that you can live without food for a very large number of days.

Fact: Some of the cravings you had (e.g. for sweets) before the MDFx, those cravings are lower or non-existent once you start eating after the MDFx. There is a (gut microbiome) based explanation for that. If you notice it happening, take advantage of it, and give up the Poison.


FAQ – Is an MDFx hard? [top]

If you try to do anything unsystematically, it is going to appear hard, or even impossible. Cruising through an MDFx is no different.

If you are systematic in your approach, you will cruise through the MDFx. If not the first time, eventually. See Discipline


FAQ – Does it get easier? [top]

From a courage and confidence perspective, every subsequent MDFx will get easier because of past experiences of success. Within a particular MDFx, as hunger disappears after the 1st, 2nd or 3rd day, it does get much easier as the days pass. It is not uncommon to hear someone doing an MDF5 say, on their day-4 “I could easily continue to an MDF10”. See Dealing with Hunger


FAQ – How often should I do an MDF5? [top]

If you are generally in good health, and also lean and athletic, an MDF5 every 6 months (twice a year) might be sufficient. I do not recommend it more frequently.

If you are generally in good health but are not lean and athletic, you could do an MDF5 ever 4 months – so not more than 3x in a year. Remember, your primary goal with an MDFx (x = 5) is not fat loss. You must improve your lifestyle in multiple ways to get to your target state of health.

If you are overweight and have realized the power of Time Optimized Feeding that can be done at zero cost to bring down your future healthcare costs, you could implement MDF5 once a month. Or MDF8 or even MDF10 once every 2 months.

See Initial Motivation and Broad Philosophy and Deeper Motivation.


FAQ – Should I do an MDFx for fat loss? [top]

If you do an MDFx, you will experience fat loss, guaranteed. The guarantee period for the loss is only those x days. You will get benefits from an MDFx that you cannot get directly if you used other methods of fat loss. So, do not do MDFx for fat loss as a primary reason, unless you have a systematic plan for the many days after the x days.

See Weight Loss and Fat Loss


FAQ – where do I sign up for an MDFx? What about the medal, certificate, and t-shirt? [top]

Because there is no money to be made from an MDFx (but I am sure someone somewhere is trying to figure out how to) you do need to register anywhere or pay anyone. There is no medal, certificate or t-shirt for participation. Only an increased Healthspan.


FAQ – Won’t I just become fat again when I start eating after MDFx? [top]

What most people think is ‘fat loss’ during their MDFx is not that – it is more water loss (from salt reduction within the body). So, after the x days, your weight will go up, because your body will again hold on to more water as you consume food with natural salt and added salt in processed foods. For more details about this point, see Weight Loss and Fat Loss


FAQ – Is there a benefit to an MDFx if it makes me feel weak and I end up spending large parts of it in bed? [top]

If your motivation to do an MDFx was religious, then you should still do an MDFx if you spend most of the last few days in bed. It is not how I would do it, given that I believe one should be as productive as possible every day, fasting or not fasting, religious or non-religious, at age 5, 50 or 100.

If you do end up in bed, when not sleeping, try to use it productively instead of watching rubbish TV. You could study, read, write, pray, meditate, speak to friends or family you haven’t connected with recently.

When you lie down to rest, it is important to bear in mind that:

[a] no storm lasts forever
[b] after some time in bed, you will feel better and be able to move around again
[c] if something is too traumatic, you might not benefit too much. It is important to keep things hormetic.
[d] complete bed rest is one of the most harmful pastimes that a smoker or non-smoker could engage in


THE PATH AHEAD – for you [top]

If you do an MDFx soon or have done one before, I would like to hear about your experience. If getting your food and drink to make you a superhuman version of yourself is something that excites you, and you would like customized guidance through the entire process, do get in touch. You can reach me by emailing me at

As always, if you have found this conversation useful, please share it with your family and friends.



Dr Purnendu Nath spends his waking hours focusing on helping individuals and organizations reach their goals, to make the world a better place. He speaks, writes and advises on topics such as finance, investment management, discipline, education, self-improvement, exercise, nutrition, health and fitness, leadership and parenting.


  1. Thanks for such a detailed article on fasting. It has changed my whole prospective towards fasting and it’s efficacy. I have had few takes from the post which I will put into practice, next time I fast. MDFx day 4 and 5 is something worth experiencing!


  2. Puru..Thanks- Very insightful – every morsel of word mentioned here, MDF2 is what i am currently experiencing and tomorrrow morning will complete 24 hours. Seems like a long journey


    • So wonderful to hear from you Shridhar. If you can go beyond MDF2, you will find that it actually gets easier – at least from the perspective of not feeling any hunger 🙂
      May the universe give you the power you deserve with your choices and actions.


  3. Puru,

    Heartfelt thanks for helping me out in my first MDF5 water fasting (i.e. for the duration 27’April-2019 at 11 AM to 2’May-2019 at 10:15 AM). The article has been a constant reference point to me i.e. prior to fast, during the fast and even after the fast.

    I had some unique and subtle experiences, had no feeling of hunger almost from end of day-2 onwards, felt lighter with a decent energy level, was able to move around, no stomach rumbling, growling or gurgling noise throughout, etc.. Also mentally there were so many instances when I was more into the moment and was quite alert. Only thing I had to deal with was mild headaches which use to come and fade away for which I just followed your instructions. I also realised it to be a very conducive state for the spiritual growth, it made me understood the reason why? fasting plays such a key role in auspicious day or religious activities.

    Overall I was amazed how my body adapted and responded to a whole fasting process. Towards the end of my fasting I had already made a decision to include periodic MDF1 or MDF2 fasts in my schedule going ahead and atleast one MDF5 in a year.


  4. Hi,

    I have read your earlier blogs too. Very helpful. I have only tried a 24 hour fast. Hunger is not the issue with me. Headaches are, and they continue even after the fast ends. Currently, I practice 16/8 only. Will definitely try this as I completely agree with the logic.
    Thanks for all your writings.

    PS: Some clues on headaches please.


    • Dear Prashant
      Thanks for writing!
      It’s simple…If you are doing 16/8 consistently quite happily…
      Simply move it to 16.5/7.5
      … then 17/7
      … then 17.5/6.5
      … then 18/6
      … then 18.5/5.5
      … then 19/5
      … then 19.5/4.5
      … then 20/4
      … then 20./3.5
      … then 21/3
      … then 21.5/2.5
      … then 22/2
      … then 22.5/1.5
      … then 23/1
      and…. you’re there!!!


      • Thank you for replying.

        Will try this gradual increment as you mention.
        Re the link for headache, I fall in the category of the 2nd para, where I am in office and also don’t think, a nap helps me. Will do try salt with water. The headache just ruins everything, continues post eating too. Hunger is not an issue though.

        Thank you.


  5. […] The volume and intensity of any recent physical activity will drive short term (acute) fatigue. Demanding physical activity will accelerate mental fatigue and it does not even have to be work you do with your limbs. Even digestion requires energy – something that is saved during short fasts or prolonged fasts. Of course, eating food will almost always leave you net calorie positive after accounting for the energy required for the digestion process. [see My articles on fasting] […]


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