5 day fasting experiment results

David Truong
6 min readJun 21, 2017

I originally posted this on Facebook, but now think it might be more interesting for the wider Internet community.

About 2 weeks ago Adriana and I finished our 5 day fast. It consisted of only water, (black) coffee, and tea. The main reason for us trying this type of fast was for general health improvements related to longevity (see bottom of post for references). Overall it was a positive experience and not as difficult as we thought it would be. This could be due to us already practicing ‘intermittent fasting’ for about a year now. The biggest surprise was how different our experience was compared to other people’s experiences — no ‘clarity’ or ‘energy high’ moments. Although we both lost some weight and body fat, I wouldn’t recommend it as a way to lose weight. It isn’t a sustainable way to lose weight. But if you’re interested in the health benefits of fasting (one of them being cell autophagy), then do your research and try it out at your own risk. 😎

Before and after ‘health’ metrics

Pre-fast (David | Adriana):

  • 74–75 kg | 64–65 kg
  • 17–18 % | 29–31% body fat
  • 77–78 % | 64.7–66.6 % muscle mass
  • 60–70 | 75–80 resting BPM
  • 6.0–6.6 | 6.1–6.4 m/s PWV

Post-fast (2 weeks after):

  • 71–72 kg | 62.5–63 kg
  • 16–17 % | 28–29 % body fat
  • 78–79 % | 66.5–66.8 % muscle mass
  • 70–75 | 70–75 resting BPM
  • 6.3–6.5 | 5.8–6.0 m/s PWV

I did have a post-fast blood test and all the signals are in the normal ranges. Unfortunately I didn’t do a blood test pre-fast, so it is hard to compare my blood results this time around.

I have been to the gym a few times post-fast and have found that my strength and endurance has diminished a bit (around 30–40%), however it is also rapidly improving to near normal levels as I continue to re-feed. I predict I’ll be back at normal gym strength and endurance within 2 weeks.

Note: I caught a cold/flu post-fast which could be due to a diminished immune system post-fast. This also likely has affected my strength and endurance, so in normal post-fasting circumstances gym strength and endurance probably won’t be reduced so drastically.

Lessons learned

  • Besides the health benefits, the other big benefit we got from this fast was how it changed our ‘relationship’ to food. Once we started re-feeding, we became much more aware of what we were eating and appreciated the good food we consumed. I also find that we are more reluctant to eat ‘junk’ food, since we’d been through this rather difficult fast.
  • For both of us, it seems that our coffee consumption has also reduced since fasting. This could be due to consuming less coffee than normal during the fast, reducing our body’s reliance on caffeine.
  • Although it was a 5 day fast, the entire process is a lot longer. Re-feeding and restoring our physical stamina (e.g. walking up stairs) took a few days. Restoring gym strength and endurance is still on-going after 2 weeks of re-feeding.
  • Our mental stamina and focus restored quite quickly shortly after our first meal.
  • Having a partner to do it with helped a lot. We could motivate and keep watch over each other, and also share/compare what we were feeling during the fast.
  • We were mainly hungry between 3pm-7pm. This is pretty close to our normal feeding time during ‘intermittent fasting’, which is interesting as our bodies seem to be used to the intermittent schedule.

Day by day breakdown

Day 1

We had just finished (an eating) holiday in Greece and stopped eating after dinner the night before. During our normal ‘intermittent fasting’, we wouldn’t have our first meal until approx. 11.30am, so the morning felt like any other day. We went to the gym (a mistake in hindsight) and went about our day. Hunger and tiredness started to set in a few hours after our normal eating time (2pm-ish). We had a nap then woke up feeling tired. Hunger would come and go every few hours, with water/tea drinking helping to subside some of the hunger pains. The day was quite uneventful. Went to bed a bit earlier than normal.

Day 2

We woke up sore and tired, which is normal for a post gym day. However I think it was a bit worse than normal due to our bodies adjusting to the lack of food in our system. We had hunger pains every few hours which were more psychological than physical pain — i.e. we just missed food and could see/smell it when going for a walk. We both started having headaches (which was expected due to lack of incoming glucose) and were both generally much more tired than usual. We kept activity to a minimum (walks, reading, relaxing). I tried to do some programming but it was very unproductive. It seems that passively consuming information was easy (reading, watching movies, etc), but trying to actively use the creative part of my brain was very difficult. I found it hard to concentrate when trying to be creative.

Day 3

Our bodies were still sore and tired from the gym on Day 1. This continued for the next day as well, which I think is due to our muscle recovery process slowing down a lot due to lack of food/nutrients/etc. We also continued to have really bad headaches. From our research, this is when our bodies should have started to enter ketosis and to produce ketones from our fat stores. However I think this didn’t happen until Day 4. I’m not sure why… maybe related to our massive (and not very healthy) meals in Greece? This was probably the hardest day as we really missed food by this point, had really bad headaches, and had already achieved the 3 day fasting milestone (the weather was also awesome outside). We did go for a slow gentle walk outside with lots of breaks, which I think helped with increasing our happiness by being outside and seeing other things (instead of just the inside of our apartment).

Day 4

I woke up feeling pretty good (no headaches or body aches), however Adriana still had some body aches. She also worked out a bit at home on Day 2, so this is probably the cause. This day was easier as we had gotten use to not eating for a few days, and the headaches had mostly subsided (yay for ketosis!). We mostly stayed at home and relaxed. We didn’t get any feeling of clarity or extra energy as other people experienced. We mostly got excited that there was 1 day left of the fast and we started planning our meal planning for post-fast.

Day 5

Similar to Day 4 with headaches mostly gone. I felt more focused than the previous 4 days, however not more focused than a normal non-fasting day. I also felt that my body was getting use to burning fat stores for energy and could probably go a few more days if I continued to push it. Maybe next time 😇. We went to bed early as we were so excited to wake up the next morning and break the fast.

Breaking the fast

Our first meal of the day is shown in the cover photo. From our research, the first meal should be rather easy on our digestive systems since it hasn’t been used in a while. Soups, liquids, soft foods, etc. It consisted of orange juice with some lime (electrolytes!), Indian soup, kim chee and Yakult (probiotics to help restore gut flora), and a serving of Feed (basically a meal replacement in powder/liquid form). Lunch was a salad with avocado, almonds and brazil nuts. Dinner was a more ‘normal meal’ with rice etc.