My 3½-day fast

Just after New Year’s, I decided to try and do a 5-day fast. As discussed in my other post from 5 months ago, I’ve been doing “intermittent fasting” (really: time-restricted eating) for over 4 years now. However, I’ve never been able to make it past 3 days. This time I was determined to learn from my past mistakes and try to make it at least 3 days and ideally 5 days. I’m definitely not as cool as MrBeast, who aimed for 30 days and ended up doing 14 days. Still, I was proud of what I accomplished and would like to continue doing longer fasts from time to time.

Why would you go so long without food?

My inspiration is Miles Kimball’s blog post documenting his “annual anti-cancer fast.” Once a year, Miles undertakes a 7-10 day fast in order to starve his body of cancer cells through a process known as autophagy.

Aside from health benefits, I would like to avoid becoming obese, and not eating for an extended period of time helps a lot with that. I also enjoy the psychological challenge of not eating for such a long period of time.

What do you consume during the fast?

Obviously, fasting means not eating. When I fast, I only drink water mixed with electrolytes (I use these sodium, potassium, and magnesium supplements from Amazon). I also take a natural fiber supplement (psyllium husks) to maintain digestive regularity. My preferred form of water is Bubly sparkling water (grapefruit or lime flavored). In particular, I found that pink Himalayan salt and grapefruit Bubly can be a delicious blend. Note that I have a hard time swallowing the sodium supplement I linked above because it is not buffered and hence upsets my stomach; therefore, I grind it up and mix it with my water instead of swallowing it whole.

I don’t drink tea or coffee, but my understanding is that black tea or black coffee are both viable drinks. For autophagy, it’s important not to drink bone broth or bullet proof coffee—two other common fasting beverages. However, these might be fine to take in if your goal for fasting is to lose weight and not kill off cancer cells.

I’m reproducing Miles Kimball’s medical advisory below (original emphasis), because it’s critical to keep this in mind before undertaking an extended fast:

1. Do not try to do a fast of more than 24-48 hours without first reading The Obesity Code, and possibly Jason Fung and Jimmy Moore’s The Complete Guide to Fasting

2. Do not try an extended fast unless you are of prime age and not pregnant: that is, don’t try an extended fast if you are a child, a teenager, elderly or pregnant.

3. If you are on any medication, you must consult with your doctor before trying an extended fast. Fasting can make the dosage of your medication wildly inappropriate. You should worry about this even with over-the-counter medication; for over-the-counter medication, lean very low on the dosage while you are fasting.

4. You should take in some minerals/electrolytes. If not, you might get some muscle cramps. These are not that dangerous but are very unpleasant. What I do is simply take one SaltStick capsule each day.

How did you feel?

The image below is a rough graph of how I was feeling as the fast progressed.

My past experiences with extended fasting have been a roller coaster, and this time was no different. In the past, I would feel normal at times and other times I would feel what I can only describe as “woozy”—light-headed, slightly dizzy, and having a brain fog. My understanding is that this is driven by dehydration.

This time, I came armed with electrolytes and plenty of sparkling water. For electrolytes, I took three different sodium, potassium, and magnesium pills. I also liberally took psyllium husks as I mentioned above.

Sleep

The main challenge I had during my fast was not sleeping well. At 34 hours, I woke up feeling clammy at 4 am and was feeling hungry. I was able to get back to sleep for a couple of hours. I only started feeling better four hours later after I drank 1.5 L of electrolyte water.

The next night, I woke up at 4:15 am (60 hours in), but I was feeling much better in terms of hunger and dehydration so I was basically up for the day.

The last night of my fast, I slept much better and woke up at my regular time.

Cold

Besides not sleeping well, I was really, really cold throughout much of the fast. This makes sense: calories are energy, and the body’s processing of food generates heat. When you’re not eating, your body isn’t generating that extra heat.

While being cold is unpleasant, it’s easy to put on extra layers, so this was only a minor inconvenience.

Why did you end your fast early?

One reason I ended my fast early was because it was Sunday and I would be attending church and taking the sacrament (i.e. communion). I probably would have just let it slide and not counted the small amount of bread as breaking my fast.

The other reason I gave up was because I missed the psychological pleasure of eating. Even though I was feeling mostly fine toward the end and wasn’t particularly hungry, I missed eating.

How much weight did you lose on the fast?

I lost 9.6 lbs over the course of my fast. 6 weeks later as I write this, I’m still 1 lb lighter than when I started the fast.

It turns out that fasting causes substantial loss of water weight. It might sound paradoxical to lose water weight while simultaneously drinking lots of water to stay hydrated. However, my rudimentary understanding is that the body’s cells hold on to a lot of water internally. When undergoing autophagy, the water that was “locked in” to the cells gets released from the body and that amount is much greater than what needs to be drunk to maintain hydration.

How were you able to continue doing your job?

I chose my fasting time strategically. As an academic, I have certain times of the year that are not busy. One such time is Dec 15–Jan 15. The timing was also good because my wife was out of town and so I didn’t need to worry about being tempted by her meals.

I still did work, but I wasn’t as productive as usual, so I wouldn’t try this during busy seasons.

Anything else you learned that’s interesting?

• Salt kills carbonation. If you throw salt into sparkling water, it immediately goes flat.

• Fat is truly a “clean fuel” for your body. I remember chasing my kids around a playground at about Hour 70. I felt completely normal and even felt a little better than usual. I could feel a difference in how my body was using energy and I liked the new feeling.

Where can I go to learn more about getting started with fasting?

• Here is a YouTube playlist I put together with some good introductory resources.

• Miles Kimball also has a nice overview here.

Note

Here is the code to produce the graph above.