MDF5 – The Log Blog

Fresh and Happy with No Food for 5 days


A 5-day water-only fast, an MDF5, is not as difficult as it sounds. Certain aspects of my first experience with an MDF5 might help you do yours more smoothly. Are you ready to feel more motivated, empowered or even just inspired?

Here are descriptive graphs, a few helpful videos, and an article about my experience.

First, a welcome video:


There are 3 more videos below on blood samples, urine ketones, and the 5th day.
For ease of navigation, to allow you to jump to the parts that interest you, here is a hyperlinked content list.



A R T I C L E   G R A P H S   &   V I D E O S
Background to This
Background Reading
My Background and Benefits
Deeper Motivation
Why those Dates? (+video)
Pre-MDF5 Activity & Nutrition
MDF5 Physical Activity
MDF5 Non-Physical Activity
MDF5 Nutrition
Ambient Temperatures
Blood Ketones vs Urine Ketones
Measuring Urine Ketones Yourself (+video)
Kg Loss vs Fat Loss
Journaling (+video)
Would I ever do another MDFx?

The Path Ahead
For you


Background to This [top]

In the detailed Multi-Day Fasting – A Guide I mentioned the importance of journaling the process. With the desire to execute your first MDFx if you understand some of the experiences of others, it will be one more encouraging perspective and supportive pillar. It is with that in mind that I decided to present this today. I hope that you will find it very useful.

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


Background Reading [top]

I strongly recommend that you read Multi-Day Fasting – A Guide before you implement anything below. And, within that, do read the articles in the sections on The Science and Benefits, on My Articles on Fasting, and Scientific Studies.

Remember, this is about my experience. We are all different. Your experience may well be even more wonderful than mine!


My Background and Benefits [top]

I have been fasting for almost 30 years now – but they have been fasts that lasted between 14 and 30 hours. There have been 3 phases in my ‘fasting life’ over the last 30 years.

Initially, intra-day fasts were only during Ramadhaan (30 days each year), typically at the lower end of that 14-30 hours range. More recently (3¾ years ago) came the everyday fasting that I prefer to think of as Time Optimized Feeding and has reached an equilibrium of about 22 hours of daily fasting. This is possible because of my Ekahari lifestyle (2¾ years now) in the most recent phase.

Each duration and type of fasting introduced at different stages of my life has had a specific set of benefits. There exist many benefits that are common to them and some benefits that are specific to only one or two types of fasting.

In order to get a different set of benefits that were previously unachievable with these comparatively shorter hours, I decided to do my first MDFx in March 2018 and set x=5. The idea was to eat no food and drink only water during those 5 days but, other than that, to conduct life as normally as possible.


Deeper Motivation [top]

I did not need to take myself through an MDF5 for fat loss. (My body fat measured last Friday was 6.5% in a gym in London.) At a physical health level, I was keen to capture the other physical benefits of fasting that we obtain when we go beyond the 96 hours mark. The deeper motivation was for imposing multiple hormetic stresses for benefits in the mental, emotional and spiritual dimensions. The access to those dimensions is, of course, through our physical world and thoughts.

Life Tip: remind yourself daily the truth “I am not my body and I am not my mind – they are both just my tools


Why those Dates? [top]

The Rough Plan

I chose a period of 5 days when I was not travelling. In London, to get blood work done privately beyond the free NHS is expensive and so makes no financial sense. I specifically chose to do my first MDF5 in Mumbai so as to be able to collect blood samples daily and get specific parameters measured by a path lab at a reasonable price. [If you want to run similar experiments, do get in touch with me at]

My first MDF5 was from 1230, Monday 5th March 2018 until 1430, Saturday 10th March 2018.

I went 2 hours over the 120 hours because I had a childless couple booked in for lifestyle counselling at the fertility clinic where I often see patients when I am in Mumbai.


Pre-MDF5 Activity & Nutrition [top]

The day before I started was a Sunday. As is typical for a Sunday morning, I ran my longer-run-of-the-week, this time a half-marathon distance, on the seaside roads of Mumbai. As is typical, I ate my Brunchnner, my one-meal-of-the-day, in the afternoon. As is not typical, I ended up eating a snack in the evening at the poolside of a sports club with an old school friend. An eating window of 5hr-45min as opposed to less-than-2-hours.

Don’t copy thy neighbour

On the morning of day-1, as part of my last meal before the MDF5, I ate breakfast as early as 10:25am which is highly unusual (median fast breaking time in the 2 weeks prior to that was 1:45pm). This is because the plan was to start the 5 days of water-only fasting at 1230. I finished my eating that morning with some nuts, fruit and vegetables and 4 besan laddoos that were homemade. I started my breakfast at a different sports club from the one the evening before and the yummy laddoos were consumed at the same clinic where I started and finished my MDF5.

So, I had an eating window of 2hr-5min on the morning that I started my first MDF5.


MDF5 Physical Activity [top]

No running during my first MDF5
No running during my first MDF5

Workouts: As this was my first MDF5 I was interested in exploring my own previously unexplored space with prudence. Normally, I would have run twice during Mon-Fri and visited the gym thrice. I decided to avoid distance running and stick to only strength training at the gym.

Other: It was important to not disrupt all the other activities of daily life. So, I continued to walk, cycle and take the train to commute to places. Some of the travel included taking stairs while carrying my bicycle. Although Mumbai is fairly hot and humid at that time of the year, prolonged fasting keeps your extremities cold while trying to preserve your core body temperature. So, the high temperatures did not feel very uncomfortable.

See the sections on Transportation and on Ambient Temperatures below.

Your strength comes from within
Your strength comes from within


MDF5 Non-Physical Activity [top]

My work carried on as usual throughout the MDF5. Other than slight irritation and distraction only on Day-2 the mental focus was extremely high throughout the 5 days. My days were spent on a lot of study, writing, programming, speaking to clients and to patients. I tend to work from the time I wake up until the time I go to bed and I rarely socialize. Things were not really any different during my first MDF5.


MDF5 Nutrition [top]

To ensure strict water-fasting, I did not consume any black coffee or other drinks. Only water. As I did not run as part of my workout regime during this MDFx I did not perspire enough to require salt intake during those 5 days.

Keep your Eating Windows short


Sleep [top]

I try to maintain good sleep hygiene – I don’t mean cleanliness, I mean factors that drive quality and quantity of sleep. During this first MDF5 I definitely slept for longer than I normally do and was very pleased about that. Maximizing sleep would further support all the regeneration of cells, including stem-cells and natural killer cells while controlling any tumor growth. Bringing down inflammation, prolonging hippocampal shutdown, and increase the learning through the night was equally important. Allowing the glymphatic system to do a deep clean for longer during sleep was a great way to complement the benefit from the ketones for brain fuel when awake.

Sleep – your Swiss Army Knife


Ambient Temperatures [top]

The “Feels Like” temperature for those days in Mumbai (and London, as a comparison) was good to note. Fortunately, prolonged fasting that allows hydration (i.e. not a dry fast) allows you to stay cooler during hot weather. Unfortunately, if you try to do the same thing in cooler weather e.g. London in March or September, you are going to need to wear extra layers during your fasting days to avoid physical discomfort from feeling cold. There are other methods to avoid feeling cold without wrapping up, but I will talk about that some other day.

You can stay warm without food


Blood Ketones vs Urine Ketones [top]

In addition to D3-hydroxybutyrate in the blood biomarkers in the plan listed above, I also checked urine ketones myself.  This is significantly cheaper but less sensitive than the quality-controlled lab readings from your blood.

It is important to note that urine ketones and blood ketones will not be strongly positively correlated. Absence of urine ketones as measured with ketone sensitive paper strips do not mean the absence of blood ketones. This is mainly because the sensitivity of ketone strips is much lower than lab equipment for measuring blood ketones. It is also the case that moderate levels of blood ketones (after 48 hours) do not mean that your level of ketosis is low. It may, in fact, highlight that you are in deep ketosis but your body and brain have adapted well to consume the ketones being continuously produced. In this case, the bulk of your adaptation did not happen during the MDF5 but because of other disciplined Time Optimized Feeding (e.g. long daily fasts) that you will have gone through prior to your MDF5. Correspondingly, if your path lab reports that you have very high blood ketones, do not rejoice too much. It may well imply that your body has not adapted its machinery to utilize the ketones being produced – you have definite scope for improvement. I believe that when in a steady state of ketosis after, say, 72 hours, you should ideally see moderate-to-high and not very high ketone levels.


Measuring Urine Ketones Yourself [top]

Here is a list of simple things you need:

  • A watch with seconds that is not your smartphone
  • Your smartphone that has a working camera
  • The ketone strips (e.g. Keto-Diastix® by Bayer)
  • Your urine sample in a clean container.

Here is my video that shows you how. Please pay close attention to the details.


Kg Loss vs Fat Loss [top]

Hopefully, you have already read this section on Weight Loss vs Fat Loss in the Multi-Day Fasting – A Guide.

Fat Loss is not the same as Kg Loss


Transportation [top]

Trying to stay green… fasting or not!
Want background reading? Here you go, in chronological order:
How Green are my Movements? 100 Days of Data
How Green are my Movements? 1001 Journeys Later
How Green are my Movements? After One Year of Logging
How Green are my Movements? 5000 Journeys Later

Move green when you can’t eat greens


Journaling [top]

For my first MDF5, I maintained a more detailed daily journal than I normally do. I have benefitted from that now, as I can look back and observe what was happening then in my mind and outside my body that I had forgotten about. In addition to typing notes and numbers into my devices, I took 149 photographs and shot 44 videos as they were often more efficient at capturing my thoughts and things happening around me. That has helped me with having this conversation with you today, 1½ years later.

Here’s a glimpse into my Video Diary for Day-5:


Would I ever do another MDFx? [top]

Other than the few minutes during Day-2 when I asked myself “why on earth am I doing this?” and then reminding myself of the host of reasons, I was excited about making MDFx part of my annual lifestyle planning. In addition to maintaining an Ekahari Lifestyle, and maintaining it as a dry fast (no-water/drinks) during Ramadhaan, I planned to repeat versions of the MDFx again. As I discussed (HERE) I did not make any decisions about when to do the next one until a few weeks had passed.

I then did an MDF8 six months later during Paryushan (Sep-2018) and then another MDF5 in March 2019. If things go according to plan, I will do an MDF8 again during Paryushan (2019) that starts this weekend.


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. […] 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 […]


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