I didn’t eat food for 4-days, here’s what happened

You’ve heard the benefits of extended fasts, but what actually happens?

I decided it’s time. Time to do an extended fast. It’s been on my list all year. Number 9. Do a 3-day fast and make a video about it.

I decided to document my first extended fast as it happened on Twitter. View the thread here.

Why fast for 3 days?

I learn things best when I’m in them. One of my rules is I can’t talk about anything where I don’t have skin in the game. I’d never done an extended fast but being a health nerd, I’d heard of their endless list of benefits. And if you’ve listened to a Tim Ferriss, Joe Rogan, Peter Attia or Aubrey Marcus podcast, you have too.

Day 1 (Friday) — I’ve been here before

74.7 kgs (164.7 lb) this morning. Nothing out of the ordinary. I’m meeting a friend at gym. We do a bodyweight workout, lots of crawling, lots of mobility work and then some kettlebells at the end.

Why blood sugar?

I read The Personalized Diet and learned blood glucose response to food can be an indicator of potential health issues. Too big a spike in blood glucose, from eating the wrong food or eating too much can lead to too much insulin being released. Insulin is a growth hormone. Too much growth leads to excess and as I realised earlier, excess leads to disease.

The parameters I tracked during my fast using this Airtable.

I don’t miss food as much I as I miss the ritual of food.

I go to bed for the first time I can remember without eating anything since the night before. 26-hours into my first extended fast.

Day 2 (Saturday) — Learning whilst doing

I wake up naturally, go the bathroom and weigh in at 72.4 kg (159.6 lbs). My mouth is dry. Nothing which can’t be fixed with a few cups of water. I record my sleep quality as 5/5 and measure my waking blood glucose. 4.2 mmol/L on meter 1 and 4.0 mmol/L on meter 2.

A urine strip showing blood ketone levels of between 1.5 and 4 mmol/L.
A urine strip showing blood ketone levels of between 1.5 and 4 mmol/L.
An exciting moment. My urine revealing I’m in a state of ketosis.
A graph from a study showing how the hunger hormone Ghrelin decreases as fasting goes on.
A graph from a study showing how the hunger hormone Ghrelin decreases as fasting goes on.
As fasting time increases, levels of Ghrelin decrease. Source: https://www.ncbi.nlm.nih.gov/pubmed/15522942
Two blood glucose meters, one showing 3.4 mmol/L and the other showing 2.8 mmol/L.
Two blood glucose meters, one showing 3.4 mmol/L and the other showing 2.8 mmol/L.
Day 2, 4:48 pm, the lowest levels my blood glucose levels have been so far.
Tracking an extended fast with the Zero fasting app. The app shows 49-hours and 23 minutes spent fasting.
Tracking an extended fast with the Zero fasting app. The app shows 49-hours and 23 minutes spent fasting.
Tracking an extended fast with the Zero fasting app. The app shows 49-hours and 23 minutes spent fasting.

Day 3 (Sunday) — Intermittent sleeping

6:45 am wide awake.

My first official blood ketone measurement with a lifesmart meter, it shows 3.6 mmol/L.
My first official blood ketone measurement with a lifesmart meter, it shows 3.6 mmol/L.
Day 3, 12:42 pm, my first blood ketone reading.
Tracking an extended fast with the Zero fasting app. The app shows 72-hours and 20 minutes spent fasting.
Tracking an extended fast with the Zero fasting app. The app shows 72-hours and 20 minutes spent fasting.
Officially crossing the 3-day mark. 3-days was the goal from the start but by late afternoon of day 3, I decided to do 4.

Day 4 (Monday) — Business as usual

8:30 am. I’ve been awake for half an hour reading in bed sipping water. No wake-ups last night but I woke up feeling as if my sleep wasn’t ideal. I rate it 2/5 in my journal.

Two blood glucose meters, one showing 3.0 mmol/L and the other 2.7 mmol/L, one ketone meter showing 3.5 mmol/L.
Two blood glucose meters, one showing 3.0 mmol/L and the other 2.7 mmol/L, one ketone meter showing 3.5 mmol/L.
Day 4, 8:54 am, still in ketosis (3.5 mmol/L) and my lowest blood glucose readings so far.
Screenshot of the Zero fasting app showing a time counter of 96 hours and 22 minutes, my four day fast is complete.
Screenshot of the Zero fasting app showing a time counter of 96 hours and 22 minutes, my four day fast is complete.
The Zero timer officially ticking over. My first extended fast complete.
My first meal to break the fast. Steak, greens, olives, cauliflower, pickles and my favourite food, almond butter.
My first meal to break the fast. Steak, greens, olives, cauliflower, pickles and my favourite food, almond butter.
My first meal in four days. Although I’m not hungry, I’m ready to break to my fast.

Takeaways and findings

Tracking blood glucose and ketones every couple of hours is tedious. The hardware could be improved. There were times I forgot and times where I didn’t take a measurement because I was doing something else.

Blood glucose (mmol/L)

I used two meters to compare different values. One of them was consistently lower than the other. The consistency of one being lower than the other was a good thing. If they alternated between one being higher or lower, the accuracy of each would be in question. My blood glucose levels were usually lowest in the morning and generally increased with physical activity. The more intense the activity, the heavier the increase in blood glucose.

Graph showing my blood glucose changes over the four day fast measured with the Accu-Chek guide.
Graph showing my blood glucose changes over the four day fast measured with the Accu-Chek guide.
Blood glucose measurements (mmol/L) with the Accu-Chek guide blood glucose meter, coloured dots indicate a measurement taken after physical activity.
Graph showing my blood glucose changes measured over the four day fast, measured with the Contour Next blood glucose meter.
Graph showing my blood glucose changes measured over the four day fast, measured with the Contour Next blood glucose meter.
Blood glucose measurements (mmol/L) with the Contour Next blood glucose meter, coloured dots indicate a measurement taken after physical activity.

Blood ketones (mmol/L)

I didn’t get ketone measurements until day 3. By then I was already in ketosis. But by the urine strips (I didn’t record these), my ketone levels were flatlining up until just before this time anyway.

Graph showing my blood ketone measurements over day 2 and day 3 of the fast.
Graph showing my blood ketone measurements over day 2 and day 3 of the fast.
My blood ketone levels (mmol/L) throughout day 3 and 4 of the fast.

Weight changes

My weight didn’t change as much as I expected. It even went up on Day 3. This is probably because it was the morning I drank 2-litres of water after waking.

Graph showing weight changes during my four day fast.
Graph showing weight changes during my four day fast.
My weight changes during the 4-day fast. I finished 2kg lighter than when I started, from my eyes, most of this seems like water weight.

Numbers at a glance

It was interesting to see how the two blood sugar meters differed. Meter 2 was consistently lower than meter 1 but they both finished with the same standard deviation (amount of variation in measurements). Note how my hunger level stayed an average of just over 1/5.

Mean, min, max, standard deviation of my blood glucose, weight, blood ketones, hunger levels and energy levels throughout.
Mean, min, max, standard deviation of my blood glucose, weight, blood ketones, hunger levels and energy levels throughout.
Mean, min, max values of some of the different parameters I was tracking during my first extended fast.

Progress pictures

These aren’t perfect. I took them as I was recording a clip for the video version of this article each morning. Each has slightly different lighting and were done at slightly different times. Day 5 also uses an iPhone instead of my camera.

Progress photos in mirror showing changes from day 1 to day 5, after the fast. Day 5 taken with different camera.
Photos I took every morning. Should be taken with a grain of salt since not every photo is the same lighting or exact same time. Day 5 is the morning after my first meal.

Extras

Despite the trackable parameters, I learned eating habits kick in even when you’re not eating. My hunger increased (not anything dramatic) around mealtimes like clockwork. Remember the 4:00 pm apple and almond butter? Every day at 4:00 pm a switch went off reminding me of this.

What would I change?

  • Water only — If you count the black coffee, I didn’t really do a true water-only fast. This is something I’d change for next time. Water and electrolytes only.
  • Low carbohydrates beforehand — The hardest part of the fast was when I was switching from burning glucose to burning fat. It was nothing unbearable but eating low carbohydrates or being in ketosis a week beforehand would probably rule out almost all discomfort.
  • Ketone measurements from the start — This ties into the previous point. It would have been helpful (and cool) to know my blood ketones from the start and all the way through to see how they changed.
  • Measurements — My method of taking measurements is still imperfect. In an ideal world, everything would be at the same time each day, weight, blood glucose, blood ketones. But most of the time reality isn’t ideal. I’m currently looking into a continuous blood glucose monitor to help fix this.

What next?

This was an experiment to learn more. And I did. I learn best when I’m in the middle of something.

I play at the crossroads of technology, health and art. Broadcasting from: www.mrdbourke.com

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