TLDR: Lost 4,2kg in 5 days without eating, regained 1,8kg 3 days after — losing a little over 2kg

For the last couple of weeks I’ve been doing intermittent fasting (IF), slowly decreasing my feeding window. What this means is that you for example start with eating from 10 to 18 (8 hours) and fasting from 18 to 10 (16 hours). I won’t go into the details of fasting and the health benefits, but only describe my experience with my first multi-day fast.

After eating only between 12 and 18 for a week (6/18 split) I decided to try my first multi-day fast. The initial goal was to do it for 72 hours (3 days) but I decided to extend it when I was not hungry in the morning of day 4.

In the middle of the day though, I got really tired. I took a nap, en went to bed early. This was a sign for me that this was enough for the time being and I decided to break my fast the next morning.

The Rules

Don’t eat anything. You are allowed to drink only the fasting-fluids from the fasting-fluids chapter in the book: The Complete Guide to Fasting. These are:

  • Water
  • Black Coffee
  • Tea
  • Bone broth
  • No artificial sweeteners, as they can kick off the cephalic phase response, triggering hunger and insulin production.

Key takeaways

I did not keep a detailed log every day about how I felt and how hungry I was. But here are my key takeaways:

  • The first 24 hours was easy because I was already doing IF, it just meant skipping an extra meal
  • The second day was the hardest, I had to put in effort to suppress the hunger with drinking lots of water
  • Every day I noticed getting a little bit hungry around noon and six, these are the times I normally eat. Even though my body was in the fat burning mode and there was plenty of body fat to burn. The circadian rhythm did well at releasing the hunger hormones at these times
  • I did not get tired, no headaches, no loss of focus
  • I was able to continue my workout schedule, although I did feel a bit weaker at some points

“The secret is to understand that hunger comes in waves. You just need to ride out the waves.”

Excerpt From: Jason Fung. “The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended”.

Weight progress

DateWeight in at 8:00
23/07/202179,75 (-0,25)
24/07/202179 (-0,75)
25/07/202178 (-1)
26/07/202177,8 (-0,2)
27/07/202176,6 (-1,2)
28/07/202175,8 (-0,8)
29/07/202176,5 (+0,7)
30/07/202177 (+0,5)
31/07/202177,6 (+0,6)


Here’s what happened; nothing. Well no nothing, my body got busy on repairing itself and started using ketones as the primary fuel source, instead of glucose (sugar). I got really tired on he fourth day and was happy to not have a 9-5 office job, I would not have been able to focus properly. I’m not sure why I got so tired, but I guess my body was done with the fast and really wanted some calories to start burning.

It is super weird to experience 5 days without food, and be completely fine. I was able to exercise, had normal focus, was not super hungry (got les every day) and not hangry. My weight went down rapidly which is to be expected. I was not eating any salt of course so I lost a lot of water weight as well. This is quickly regained as when you start eating again. The expected fat loss is around ±0,25kg (half a pound) per day, so the weight loss and gain are as expected.

250grams of fat is 1925 kcal (7700 / 4, where 7700 is the amount of kcal per kg of body fat)