Tuesday, October 24, 2017

Fasting for 8 Days: Why? And Now what?

In mid-September I set out to fast for at least one week, drinking water but essentially no food.  I broke the fast in the afternoon of the ninth day after over losing more than 13 pounds. 

Part of me wanted to keep going because I felt exceptionally focused and calm on the 7th and 8th day.  However, I was also looking forward to finally eating again, and I had a kind of silly reason not to continue:  I had signed up for some "diet bets" that were ending a few days later, and I was worried they might flag me for losing too much weight if I didn't squeeze in a few solid days of re-feeding before the weigh-in.  

So I stopped, and I actually tried really hard to eat as much (healthy food) as I could for the next 4-5 days, mainly for the diet bets, but also for the rebuilding process that happens in the body after any fast.  It turned out eating was challenging, however, because I felt like I assume people feel after bariatric surgery:  I could only eat about half as much food as usual before feeling incredibly full.  That sensation wore off gradually over the next week-or-so as my stomach re-expanded, and I didn't have any problems with the weigh-ins.  In fact, they were the easiest "diet bets" I'd ever done... 

Why did I do something so crazy? 

First, there is growing evidence that fasting may be the best thing you do for your health.  Research and other preliminary data in both animals and humans have shown evidence for:
And the list could go on.  The most dramatic benefits come when you do more than 3 days in a row, but any duration is beneficial. 

Keep in mind I've been aggressively steeping myself in nutrition- and health-related research for the past year or so, but as I think on it now I'm convinced the only reason more people aren't fasting is because they just don't know how beneficial it can be.  And of course the fact that it goes again decades of traditional advice that was based on basically nothing...

Second, I'm convinced that fasting (intermittent, extended, or some combination) is the best way to lose weight and keep it off.  

Basically, if you cut your calories down every day (i.e. traditional advice you hear everywhere), you lose some weight until your metabolism adjusts accordingly, and then you plateau.  After that you regain the weight (and then some) when you inevitably fall off the wagon because your strategy isn't working and you're frustrated.  

When you fast, on the other hand, you don't lower your metabolism in the long run, and you keep your body guessing by switching things up regularly.  You also lower your insulin for long stretches of time, and insulin is basically the signal to your body to store fat in response to energy intake. 

For those basic reasons, I think weight loss is much easier once you have this additional tool in your belt.  

What else happened while I was fasting?

Here are the notes I took during the fast:

In case you can't read my chicken scratch or it's too busy for you, some key stats:

  • Weight loss:  over 13 pounds, or just under two per day on average.  (The two numbers listed for each day are two different scales.) 
  • Urine ketone levelsVery high all the time after day one.
  • Blood Sugar:  83 on day one, then never over 60 again; typically in the 40's.  
  • "Food" Intake:  Some sugarless gum here and there, salt, potassium, magnesium, vegetable bullion to increase sodium (about 9 cal/day starting on day 3), and some tea (no calories).  That's about it. 
  • Energy Levels:  About 20% lower than usual on average, actually felt the best on day seven and day eight out of the whole 8.5 days.  


It's been about month now since I finished the fast, and my current weight hovers around 170 lbs (10 lbs below starting weight).  That's quite remarkable really, considering you would typically expect to regain about 2/3 of the weight you lose during a prolonged fast (because of the transient components of the weight loss, in the form of water, sodium, glycogen, recycling old proteins, and shrinking down certain cell populations, such as white blood cells and various organs).  It's also remarkable because I've been regularly lifting weights in the past several weeks, so I expect I have a few more pounds of muscle now than when I started the fast.  

I think the sustained nature of my weight loss is a testament to what I've done since then:  Additional fasting, and avoiding refined sugar and refined flour at all times.  I've been in nearly-continuous ketosis since the week before the fast, and that's despite eating a lot of berries, and sometimes even oatmeal, legumes and other fruits, including bananas and oranges.  The sustained weight loss is also further evidence of how well fasting works as a tool for weight loss.  

If after reading this you're thinking of trying some type of fasting, you are wise individual indeed. :)  However, to approach it smartly, here's what I'd suggest: 

  • First, start by cutting out refined sugar and other refined grains for a period of time, perhaps 1-3 months, and ideally doing a full-fledged ketogenic diet during that time.  It will be a lot easier to fast if you're already in ketosis, and after your body has some time to get used to using ketones for energy.  Interestingly, ketones both curb hunger and inhibit muscle breakdown.  Chew on that. :)
  • Second, Start with time-restricted eating (12, 10, 8, or 6 hours in a day).  The clock starts when you eat your first caloric substance, and stops when you eat your last, and you try to keep it below whatever time you set.  The simplest way to do this is to skip breakfast or dinner.  This is a form of intermittent fasting, and basically gives your body an extra 6-8 hours with low insulin levels, and at least a slight bump in ketone levels. 

Either or both of those methods will help you to ease into it, and after that there are myriad options of how to approach it. 

Personally I plan to continue regular fasting of some sort in perpetuity, both until I get to my ideal weight as well as thereafter for "maintenance" and additional health benefits. 



I think Jason Fung is the best person to listen to about Fasting.  You can search YouTube and find a host of Jason Fung interviews, but this is probably a good one to start with.

The Complete Guide to Fasting is a book that I haven't read yet, but after hearing the authors on many podcast episodes I feel comfortable recommending it.  

"Fasting Talk" is a podcast which has loads of insights, and I especially like the episodes in which Dr. Fung appears.  Start from the first episode because the format changed after about 20 episodes, and those first ones give a nice foundation. 

There's a lot of mention on there of using different supplements or what not while fasting, but the more I learn I think it's better to fast with nothing but water and electrolyte supplements, to get the greatest health benefit along with weight loss.  Also, the two non-physician people on the podcast are a little sensational and not-so-scientific at times, but the advice is generally good. 

Mark Mattson is a researcher who is quite expert on fasting:

Mark Mattson on stemtalk:  https://www.ihmc.us/stemtalk/episode007/

"Found my Fitness" is a science-based podcast by Rhonda Patrick on all things health and nutrition.  Several episodes relate to fasting and keto.  Here are a couple good ones to start with:

Some of the below are available as podcasts.  The first video is the one that got me started with keto a little over a year ago. 

Peter Attia video on ketogenic diet:  https://www.youtube.com/watch?v=NqwvcrA7oe8
Peter Attia stemtalk interview:  https://www.ihmc.us/stemtalk/episode001/
Peter Attia w/ Tim Ferriss:  https://www.youtube.com/watch?v=hfvH-YfbOEo

Dom D’Agostino stemtalk:  https://www.ihmc.us/stemtalk/episode-14/
Dom D’Agostino w/ Tim Ferriss:  https://www.youtube.com/watch?v=q_b8pbyFdGY

Dom D'Agostino is kind of the guru of all things keto, or the person who knows the most about keto-related research.

There's a book called "Keto Clarity" that I haven't read, but just like the book listed in the fasting section I've listened to the author on many podcast episodes and I think it would be a good resource in the early stages.


  1. Wow. Now trying for 40 days? Nice work

  2. Interesting... do you exercise while fasting?

    1. Yes, sometimes I do, but typically very modest intensity. Sometimes I do cold exposure or sauna as alternatives. If I do any resistance training it's at the end of the fast very shortly before I start refeeding, it wouldn't make much sense to break your muscles down a lot if you're not going to eat for a few days or more.

  3. I really like learning about this from you. Keep up the good work!