I can think. I can wait. I can fast… When a person has nothing to eat, fasting is the smartest thing he could do. When, for example, Siddhartha hadn’t learned to fast, he would have to accept any kind of service before this day is up, whether it may be with you or wherever, because hunger would force him to do so. But like this, Siddhartha can wait calmly, he knows no impatience, he knows no emergency, for a long time he can allow hunger to besiege him and can laugh about it. This, sir, is what fasting is good for.
— Siddartha by Herman Hesse
When I read this while traveling in Thailand, I was inspired to try an extended fast. I never thought of hunger as a handicap.
Especially when traveling, I constantly think about food and when I’ll eat next. I spend time researching, going to, and eating at restaurants. At work, there’s a constant push-pull whether I should keep working or get up and have a snack. While I enjoy eating and especially experiencing a new place through its cuisine, I often go too far. I’d get more out of a trip and have more focus time at work if I were in control. Fasting seemed like a great way to practice that control. By going beyond hunger, I’d prove to myself that nothing bad would happen. I wouldn’t pass out. I wouldn’t be unable to focus due to the hunger pangs. I’d laugh about it like Siddartha.
I’ll be skipping some plot and technical details in this narrative to keep it focused, but scroll down to the last section for my detailed log, or the section before it for the science.
I just happened to read Tools of Titans by Tim Ferriss after I read Siddartha. Ferriss describes his three day fast protocol, which he does a few times a year. He begins after dinner on day zero. The next day he wakes up late and walks for a few hours to deplete his glycogen stores as quickly as possible. While his cells are switching over to ketosis, he consumes exogenous ketones like MCT oil, up to 400 calories/day. Once in ketosis, as measured in blood samples, he only drinks water with a little added salt. This continues until the evening of the third day when he eats a giant greasy burrito. Sounds easy!
I started on Tuesday after dinner. Hunger set in the next morning, but drinking tea and water staved off the worst of it. I walked around San Francisco all day and felt okay, but waves of hunger made me not even want to listen to a book. I felt present and aware, as if in a permanent mindfulness exercise. I tired easily, and sometimes stopped walking to catch my breath.
By the time I got home in the evening, I was completely spent, brain at ~30% capacity, and felt cold, but not hungry! My body was shutting down. I cranked up my electric mattress pad and passed out. When I woke up five hours later, I felt pretty good and my urine test strips showed I was starting to enter ketosis.
When I woke up Thursday morning, I felt weak and lightheaded, with brain capacity at 30%. A urine test strip showed high ketone levels. I strongly considered abandoning the experiment due to the brain fog, but decided to allow myself a few more calories in the form of straight coconut cream. Rather than hunger, I just felt slight nausea and an emptiness. Over the next few hours I had about 400 calories and each time the nausea ebbed. I’m not sure how much of that was placebo, but it worked. I felt I had 70% mental capacity, but I proceeded to hammer out tasks. I wrote a letter, did some brainstorming, interviewed someone, and a couple other things. A trance-like focus propelled me along. I felt foggy when not actively working on anything, but good while working.
As the sun set on Thursday I had felt weak and foggy for hours. I decided I had gotten what I came for, so I’d abort one day early. I planned to meet friends at El Farolito for a victory burrito. I worried I’d be too weak to get there, but wanted to test myself. As I walked out the door, I suddenly felt normal. To catch the bus I had to walk fast and even jog a bit. In the moments where I needed the extra energy, it was there for me. My heart beat a little faster and I breathed a little harder than normal, but otherwise I felt good. At one point I felt the urge to water poop, but successfully held it in. When I sat down in the bus I felt foggy, weak, and cold again.
When I got to the restaurant, I chatted with my friends while we waited for the burritos. I still wasn’t hungry, but in conversation I felt pretty good. I considered continuing the fast and saving the burrito. If I were starving, I would’ve attacked it the moment it came. It came. I felt no particular urges. But as I bit in, the symphony of chorizo, avocado, beans, rice, salsa, cheese, and sour cream filled my mouth, bombarded my senses. It was one of the most delicious things I’d ever eaten. I stopped half way through to take stock. I felt good. My brain fog was clearing. I felt warm and took off my jacket. I started eating the second half.
With a fifth of the burrito still sitting on the plate, strong nausea brewed in my gut. I wasn’t sure if I needed to poop or vomit, but I knew one of the two would happen soon. I interrupted the conversation with an understated “I might need to throw up” and walked as fast as I could manage to the bathroom in the back of the restaurant. Just before I got to the door, my vision darkened and my strength left me. I managed to make a semi-controlled fall to one knee. Some guy was standing there. I pushed the words out of my mouth as if extruding clay: “Can you help me?”
“Have you been drinking? Are you ok?”
WARNING: graphic content in following paragraph
“I fasted for two days. I just ate a burrito. Need toilet,” I replied. My words sounded like a bad joke, but I was too deep in emergency mode to laugh. He helped me into the bathroom and left. I staggered to the door, locked it, and felt my butt start to release. I made a split second decision whether pooping or vomiting was more urgent. Poop. I made it to the toilet, sat down, insides rocketing out of my asshole in a foul brown stream. Full consciousness flooded back in. Sweat poured from my face, covered even my thighs. I saw the trail of liquid poop droplets from the door. I looked to the toilet paper dispenser and found it empty. I didn’t care. Relief, gentle nausea, and thoughts of my friends swirled in. With my friend’s help, I cleaned up and got in a Lyft home. “What’ve you learned?” she asked.
“It was a supposedly fun thing I’ll never do again.”
At home I cleaned up more, went to bed, and passed out. When I woke up on Friday, it all seemed like a bad dream. My mind and body both felt good, or maybe even better than usual.
I embarked on this quest to defeat hunger and test the limits of my mind and body. I found those limits. I experienced total lack of hunger despite an 85% caloric intake reduction. I went deep into ketosis. I felt high without drugs. I found focus despite mental impairment. I completely purged my digestive system.
In retrospect, I’m glad I did it. I learned about myself. I regret following Ferriss’s advice to break the fast with a giant greasy burrito. Actually, I regret following any of Ferriss’s fasting protocol. He has more fasting experience than I do, and importantly it’s his own. I read his guide a couple of times to make sure I was following it to the letter. There were not enough warnings. What worked for him didn’t work for me. It was potentially dangerous.
If I were to try it again, I’d work up to it. A couple one day fasts with no calories at all? Try to get into ketosis before starting to fast? The MCT oil gave me the diarrhea. Skip that. Then, I’d very carefully re-feed. A slice of bread over 30 minutes?
I probably will not try it again. To anyone considering this, please approach it more seriously and gradually than I did. Don’t trust anyone’s advice. Use your own gradual experience as your guide. Listen to your body. Bail at the first sign of trouble. You can always try again.
Before I began, I wanted to make sure I knew what I was getting into, and to be able to explain what I felt physiologically. I’m not a biologist, so please fact check me!
There are two energy sources in the body: glucose and ketone bodies. When people talk about blood sugar, that’s glucose. It’s the most immediately available of the two, so cells use that first. When you’re running low on glucose, the liver starts breaking down its glycogen stores into glucose. If your glycogen stores are full, incoming sugar will be stored as fat instead of more glycogen (aka de novo lipogenesis). If you’re low on glucose and glycogen, fat cells (adipose tissue) will release more free fatty acids into the blood stream.
Ketone bodies come either from metabolism of these free fatty acids or directly from food. Under normal circumstances, there’s plenty of glucose floating around, so the liver doesn’t produce ketones. During intense, prolonged exercise or during fasting, though, the body starts to get some or all of its energy from ketones (ketosis). In Ferriss’s fasting protocol, you purposely walk all morning to try to deplete your glycogen stores and get to ketosis faster. The danger here is that the body may also try to break down muscle into amino acids into glucose (gluconeogenesis) instead of using fat.
I think it’s for this reason that Ferriss recommends consuming straight ketone bodies in the form of medium chain triglyceride (MCT) oil. Cells can use these MCTs directly. By ensuring there are enough non-glucose energy sources in the body, it won’t resort to breaking down your muscles. But MCT oil can also cause massive diarrhea since it is anti-bacterial! Fasting alone didn’t cause my diarrhea, so the MCT oil is the only possible culprit. The diarrhea probably also caused some of the weakness and lightheadedness.
I’m guessing that by the time I at the burrito, my intestinal tract was full of water, and the digestive pump (peristalsis) had shut down. When the burrito came in, everything suddenly came back to life, and it only took a little push for all that liquid to get evacuated, leading to my explosive diarrhea. I’m not sure why it triggered massively increased heart rate, breathing rate, sweating, and in general my autonomic nervous system’s complete rebellion. Some chemical processes were finding new equilibrium very quickly.
The reason my brain got so foggy on day two is that it takes 3–4 days for the brain to switch over to using ketone bodies for energy. It’s not a step function, but a slow transition. Presumably if you frequently go into ketosis, that transition period would shorten. This was the worst part for me, and the primary reason I decided to abort my fast early. People whose brains have switched energy source to ketone bodies report a sense of unusual mental clarity. This may be due to ketone bodies producing more cellular energy (ATP) per oxygen than glucose. Or it may be due to having been mentally impaired for the last 3–4 days. I haven’t seen conclusive evidence.
Day 0 — Tuesday
- 8pm: Split a vegetarian Souvla salad
- 11: Sleep
- 7am: Bike to Mission Cliffs, lead climb 1 hour, bike home
- 9: Drink a pot of rooibos with Jack
- 11: Go home, chat with Chris, stretch, normal poop, shower, drink 1 tablespoon MCT oil (140 calories)
- 12: 3L of water in a backpack, walk all over SF, listen to Superintelligence at 1.5x speed
- 4:30: Return home feeling really light headed and cold. Drink 1T oil. Liquid poop.
- 5:00: Turn on electric mattress pad to near max, pass out
- 10:30: Wake up to chat with Ariel, take metamucil and melatonin. Ketone test strip shows 5 mg/dL
- 11:30: Sleep
- 6:30: Wake, check keto levels (above). Maybe a little too high! Feel very weak, drink 1T oil
- Make “keto ice cream”: freeze 2c coconut cream, 1T cocoa powder, 2 pinches sea salt, dash cinnamon
- Read a lot on fasting dynamics: how much electrolytes to consume, what are the expected side effects, etc. Realize I might be getting too much salt and water
- Nice solid poop thanks to metamucil from yesterday
- Feel terrible, eat some keto ice cream, feel slightly better
- Onboard a bunch of accounts for new job starting Monday
- Finish watching Fantastic Beasts
- Hand-write a letter to a friend
- Prep for and interview CEO of a startup that I had cold-emailed
- Check keto levels (above)
- Water poop again
- Write most of this post
- Water poop again
- 6:30pm: Walk to bus, take bus to Mission
- 7:00: Meet Ariel and Razzi at El Farolito for chorizo super burrito. Devour burrito with intense pleasure
- 7:30: Break out in sweat. Interrupt Razzi, rush to bathroom, fall over near the door, make it inside, poop my pants a little, sit on toilet, completely evacuate bowels. Clean up. Lyft home.
- 8:00: Get home, shower, hydrate, pass out
- 7:00am: Wake up, feel great! Eat a banana and some chips.