Seven-day (~170 hours) fast 

  Breakfast is for gluttons and peasants – Thomas Aquinas[*]

I decided to write this short account of my fast because of the overabundance of blogs prescribing conflicting things about fasting.  Also, reputed sources focus on short-term fasting (less than three days), and mostly on intermittent fasting (time-restricted eating).1–3 Most sources on longer fasts are blog entries, and one should take all of these (this one included) with skepticism.  So, on to the fast…

The fast consisted on avoiding food completely for seven days.  I only drank filtered water.  No vitamins, no electrolytes, no teas, no coffee, no lemon; nothing but water.  Here is what happened:

Day one

Feeling irritable and experiencing brain fog.

Night one

Sleep is interrupted.  I would attribute this interruption to the lack of food intake.

Day two

Feeling lethargic and brain fog.

Night two

Sleep is again interrupted and experienced dizziness when rising in the morning.

Day three

Hunger is gone.  Aches all over my body, especially in my legs.  Have become much more sensitive to the cold.  The strength of my urinating stream is somewhat diminished.  My mind is reactive (as opposed to proactive), meaning that watching movies (as opposed to, for example, writing) was the activity on the docket.

Night three

Sleep was not interrupted.

Day four

On the fourth day I felt very tired even after having slept over ten hours.  After spending 3-4 hours awake but in bed, I started having mental energy.[†]  I also perceived a stronger and faster heart rate, which I measured at 50 BPM.

Night four

It was difficult to go to sleep.  Slept 7 hours.  Sleep was interrupted by a short period of fantasizing about food, and afterwards by feelings of starvation as well as palpitations.  Specifically, a sucked-in abdomen with the feeling of my digestive system scraping my stomach for food, and a perceived thumping heartbeat.

Day five

55 BMP.  Feelings of starvation are gone.  Feeling normal.  I believe I am now in a full state of ketosis.  I am producing energy from fatty acids (not too much energy, but enough energy to carry out daily tasks).  This is accompanied by a fruity-iron breath (ketosis breath).  Intermittent feelings of starvation.

Night five

More fantasizing about food when trying to sleep.  General difficulty sleeping.  It seems my body is telling me to get up and find food.

Day six

BMP 60.  Feelings are the same as in day five.  With the addition of boredom, I am now bored of the fasting effort.   Tried to be proactive and was mentally exhausted within a short period of time.  Mind works for menial tasks like reading the newspaper, listening to a podcast, watching a light film, getting a glass of water.

Night six

More difficulty sleeping.  Slept for five hours.

Day seven

BPM 65.  No hunger.  Energy for cleaning, walking to the store.  Ketosis breath less noticeable.  Do not feel like refeeding, even though I will feed before bedtime.

Refeeding day one:

Broke fast with raisins and orange juice.  An hour later I had Greek yogurt with no added sugar.  I was feeling great until I had some peanut butter.  I felt tired after the peanut butter and went to sleep.

Refeeding day two

Ate normally.  Began the day with a complete eggs-based breakfast.  Had chicken later in the day.  Everything normal.

Overall experience:

I lost 9% of my body weight.  By the second day after breaking fast I regained 2% of my original weight.  By the third day I stood at 95% of original weight.  Bowel movements occurred until day three and on day six of the fast.  The daily increasing of BPM at rest is weird, however I would attribute this to errors in measurement, as these were measured the old-fashioned way with a clock and two fingers on the carotid artery.

I would consider that fasting for seven days is safe for most people.  This opinion is not only based on my personal experience but on an actual study carried out on 768 people.[‡]  It seems most people experience manageable adverse effects when completely restricting food for up to 21 days.  These adverse effects rise consistently until day ten and then begin to plateau until day 21.4  I should note, however, that in the mentioned study there were two hospitalizations due to complications due to fasting, indicating that the body is being put through strain.  So, I support the recommendation to plan any fasting exercise with the guidance of one’s doctor.

I do not see meaningful benefits in fasting for health.  It is an efficient way to lose weight, but I did not experience a mental clarity nirvana, nor feelings of splendorous energy as has been reported in other accounts.

Nevertheless, I do find spiritual value in the experience.  It teaches the fasting individual about scarcity, restraint, and discipline.  Meditation is key.


[*] Paraphrase.

[†] I read academic articles on fasting and then watched films.  Read literature before going to bed again.



  1. Intermittent Fasting: 4 Different Types Explained. Cleveland Clinic. Published April 30, 2019. Accessed January 3, 2022.
  2. Is intermittent fasting good for you? Mayo Clinic. Accessed January 3, 2022.
  3. MPH MT MD. Intermittent fasting: Does a new study show downsides — or not? Harvard Health. Published October 30, 2020. Accessed January 3, 2022.
  4. Finnell JS, Saul BC, Goldhamer AC, Myers TR. Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting. BMC Complement Altern Med. 2018;18:67. doi:10.1186/s12906-018-2136-6
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