I also blog frequently on the Yesod Web Framework blog, as well as the FP Complete blog.

Post Fast Write-up

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As I blogged about last week, last week I did a multiday fast. There was definitely interest in this topic on Twitter, and at least one request for a post-fast write-up. So here we go.

I fasted from about 8pm on Saturday, July 7 to 8am on Friday, July 13. This works out to 5.5 days, or 132 hours of fasting. Additionally, I had done a shorter 1.5 day fast the previous week (from Thursday, July 5 till Friday, July 6), which as you’ll see is relevant to the weight results.

That previous blog post shared some of my reasons for fasting. The short version is: there are lots of potential health benefits, but my goal right now was to try to lose some fat with minimal muscle loss.

Weight change

Since the primary goal of the fast was fat loss, let me share the numbers. I always weigh in first thing in the morning for consistency. I additionally record skinfold caliper and waist measurement approximations of body fat percentage, which should be taken with a large grain of salt. I’ll include them in the information below.

Unfortunately, I forgot to record my weight on Sunday, July 8. The most recent weigh-in I’d had before was Wednesday, July 4. I took measurements on Monday, Wednesday, and Friday (just before breaking the fast), and again Sunday morning (48 hours after breaking the fast).

Finally, for context, I am 175cm tall (5’9”).

Day Weight Body fat % (est) Fat mass (est) Lean mass (est)
July 4 81.8kg 21% 17.4kg 64.4kg
July 9 79.3kg 21% 16.9kg 62.4kg
July 11 77.7kg 20% 15.5kg 62.2kg
July 13 76.8kg 19% 14.3kg 62.5kg
July 15 78.5kg 20% 15.7kg 62.8kg

Again, take the numbers with a grain of salt: body fat measurements are not perfect. A secondary measurement I’ll get to in the next section is changes in lifting strength. Here are some takeaways:

  • There was a precipitous drop in weight right after starting the fast. This is expected as a loss of water weight.
  • Similarly, I put on almost 2kg of weight again in the 48 hours following the fast. This is again expected as I was regaining water weight. (I ended up eating around 100g of carbs over the course of Saturday.)
  • There was a relatively steady weight loss during the course of the fast.

To me, it looks like I lost between 2-3kg of fat from the fast, including the 1.5 days the previous week. This would come out to between 15,400 and 23,100 calories, which would mean between 2,369 and 3,554 calories per day. All of which sounds perfectly reasonable given my weight and activity level.

Strength during fast

There is a major confounding factor in measuring my strength: I’ve been recovering from a wrist injury which has affected all of my major lifts (squat, deadlift, and bench). That said: I had no major drop in strength measured by a 5 rep max during the fast. I did tire out more quickly on subsequent sets, however. I’ll have a better feel for whether I had any strength loss over the coming week.


This was by far the easiest fast I’ve ever tried. The second day was, as usual, the hardest day. But it wasn’t really that difficult. I had a high level of mental focus, had plenty of interesting (and some non-interesting) work tasks to perform, and plenty of phyiscal activity. In other words, I was able to distract myself from eating.

There were a few times during the week when the hunger was intense, but only for 1-2 hours at a time. There were a few times when I didn’t feel like I could focus on anything, but that seemed more to do with an overabundance of things grabbing my attention than the fast itself.

I had decided in advance that I would break my fast Friday morning. I was certainly excited to get back to eating, but when I woke up Friday morning, I did not feel ravenous, nauseous, or in any other way in need of breaking the fast. Had circumstances allowed it, I have no doubt that I could have easily kept going.

Hunger after fast

Usually after a fast it takes me a while to feel properly hungry again. I broke my fast on a (for me) relatively light meal of 2 scrambled eggs. Twenty minutes later, I added in some cheese, and then took the baby for a walk to visit my parents. That’s when the hunger really kicked in. I started snacking on anything I could get access to. I came home and fried up a pan full of tuna. I continued eating a lot throughout the day, finishing off with some large pieces of meat Miriam made for dinner.

Saturday felt much the same, though Miriam seems to think I ate less than I thought I did.

I neither measured my food intake, nor tried to restrict it in any way. As you can see from the weight chart above, between Friday morning and Sunday morning, I put on 1.7kg, which I believe would be entirely accounted for by water weight. I don’t believe I had any fat gain or “refeeding” issues,” though I acknowledge that the body fat estimates paint a different picture.

Plans for the future

This was a win for me. I have to see if it significantly impacts performance in the gym, but otherwise, I found this far easier than trying to do a prolonged weight loss “cut.” Assuming all goes well, I may try to do alternating weeks of eating a high fat, moderate protein diet, followed by a week with a multiday fast (between 3 and 5 days), and see how that affects weight and strength.

I’ll continue taking body measurements, and will share results when I have more meaningful data.

If anyone has specific questions they’d like me to answer, let me know!

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