The 48-Hour Immortality Fast

by Dan Walsh

Notes and observations from my starvation-induced attempt to regenerate stem cells.

Human longevity is a fascinating subject for me . Flipping death on his head seems like the most fundamental paradigm shift that could ever occur for humanity. Imagine how everyone would change if they had more time – infinite time. Some people see doom and gloom, but I see the end of one our most corrosive driving forces: the fear that we’re running out of time.

I’m always on the lookout for new studies that point towards longer life-spans and I found an incredible one last week: Fasting Triggers Stem Cell Regeneration of Damaged Old Immune System. The study showed that fasting for 48+ plus hours triggers a regenerative process in mice that creates a fresh immune system. They’ve extended the fasting protocol to humans and found similar results. I’m kind of a diet hacker so this was right up my alley. I had to give it a try.

Now, the humans in this trial were going through chemotherapy. They had a huge incentive to stick to their fast for 48 – 72 hours. By doing so, their bodies could basically send in a new immune system right after the chemo destroyed it. I have no incentive other than curiosity and 48 hours is a long time to not eat. As far as I know, I’ve never gone that long without eating, and I don’t think I’ve ever been on a real fast before. This was new ground for me.

The following are the train-of-thought notes I took during my fast.

48-Hour Fasting Notes

I started my fast last night at 8pm. It’s almost 11am now, so I’m 15 hours in. Getting hungry. Started getting hungry on my ride into work, but it’s more acute now. Not bad though.

Two interesting observations so far:

  1. Purposefully making myself hungry is an odd departure from the norm. Usually hunger is a side effect – something that needs to be fixed. But in this instance, hunger is the point. Are there other similar feelings? Fatigue? Pain? How does my perspective on these things change when I approach them on purpose?
  2. I have realized a food-seeking behavior of which I was previously unaware. Two or three times now my mind has subconsciously gone in search of “food I can eat.” My normal diet precludes certain foods – junk food, etc – and I have adopted the behavior to search for foods that are ok to eat when I am hungry. I didn’t realize that was my model for finding food. In this instance, though, there are no foods that are ok to eat.


It’s almost 5pm now. I’ve been about the same level of hungry since lunch. Interesting that it hasn’t really increased. I had a coffee at lunch, that probably helped. The warm liquid feels good in my stomach. Might hurt later… I’ve also started snacking on a bit of salt. Not because it fills me up, but because my mouth misses… flavor, maybe? The act of consumption?

Funny, I’ve missed / delayed breakfast and lunch before, but this feels more epic because I have to go all day tomorrow too. Overall, it’s really not that bad though. I’m not in agony. I’m still getting work down. I don’t feel tired or lethargic. My mind seems capable. So far this seems like it could be a doable, monthly ritual… would be good to have actionable numbers on this process to see if it’s worth it. :)


7pm. 23 hours in. Got pretty hungry on my way home from work. Bike ride. Contemplated ending the fast. Everything sounds DELICIOUS. Even crappy stuff like Ramen Noodles. I’m drinking some apple spice tea right now to see if the warm liquid will help again. Seems to be working so far. It’s pretty easy to go a day without eating. This isn’t hard. But thinking about not eating tomorrow too! That’s the compelling reason to quit.


8pm. 24 hours. Downed half a bag of sweet potato chips and a bunch of trail mix. Felt good.


Observations and Thoughts

Yeah… so I didn’t make it 48 hours. :)

My hunger never became so incredible that I was in agony or couldn’t think of anything else, so it’s interesting to me that I cracked. Thinking about eating wasn’t an issue while I was busy at work, it was only when I got home that my mind started to spin and my willpower waned.

“Should I just end it now and try again later?”

“I shouldn’t end yet. I’m not even halfway!”

“Should I make it a 24-hour fast? That would be a worthwhile experience, right?”

That’s always the way. As soon as the “should I / shouldn’t I?” thoughts begin, the battle is already lost. Willpower can’t win that fight. The advantage is so lopsided that it’s not even really a fight.

Angélica jokes that I can stay full for a week off the thought of a single almond. I love that joke, and there’s a bit of truth there. I don’t get hungry often, which gives me an uncommon relationship to food. I sort of eat like a snake. I’m sure this made fasting easier. Even so, the fasting experiment revealed two behaviors related to hunger that I wasn’t aware of: avoidance and guided seeking behavior. These seem obvious and common in retrospect, but I had to go to the extreme to get enough perspective to see the status quo.


How To Make It Better Next Time

Well, first of all I need to make it to 48 hours. The biggest hurdle was boredom and a little fatigue. I was pretty tired when I got home after work. I should have just gone to sleep. Instead, I stayed up and became preoccupied with thoughts of the fast. I thought about how another whole day of fasting would feel (probably not great). I thought about what I should eat to end my fast (baked sweet potato). I thought about if it was all worth it. Like I said, willpower can’t handle that. Next time around, I either need to go to sleep, or find something that doesn’t require a lot of effort to keep me preoccupied. Like videogames.

Not eating for 24 hour played some tricks on my digestion. It was sort of off for the next few days, as one might imagine. Eating a spoonful of sesame seeds in a neat little trick to see how long food stays in your stomach. They don’t get digested, so you can see them when they come back out (gross!). I’ll down some seeds at the end of my final meal so that I know when everything has left my system.

I didn’t have adequate quantifiable measurements. I used a continuous heart rate monitor and urinalysis reagent strips to measure changes in my body. The HR monitor does a better job at showing changes over time – trend data. This test wasn’t long enough to use HR as a good metric, though resting heart rate may have changed during the fast and unfortunately I didn’t measure that. The reagent strips are more immediate. They showed changes to glucose levels, specific gravity, and PH, but I didn’t have a good baseline so I don’t have much to compare it to. Before my next fast I’ll work on establishing a better understanding of these metrics so I can spot changes.

Based on the experiments in the article, the biggest changes occurred in the circulatory and immune systems. Adding a few blood tests and blood pressure metrics to the next pass will give me a much better idea of what’s happening in my body.



It sounds strange to say, because I basically failed, but the fast wasn’t as hard as I thought it would be. There was no agony. My resolve just kind of melted away and then I binged on sweet potato chips. I thought it would take a lot out of me, but I felt fine after a day. It’s been less than a week and I feel like I could try it all over again. A weekly schedule is probably too much, but maybe a 48 hour fast at the beginning of the month would be a good cadence. I’ll try again August 1st.

I took another look at intermittent fasting while trying to find rational reasons to quite my fast. There’s a lot of evidence that fasting for even as little as 18 hours can have a substantial positive effect on overall health – though not the same kind of stem cell regeneration. Either way, after a 24 hour fast, 18 hours would be a breeze. Maybe I’ll try working that in more often. I need to do more research first.