Even if you're not obese, fasting appears to be one of the most healthy things you can do for your body. Low insulin variability, autophagy, clear out visceral fat on organs, yields extended longevity in lab mice, etc.
Disclaimer: I eat like garbage so it's more likely that not eating garbage is having these positive effects, not just fasting.
As mentioned from fasting you still get major benefits from autophay, sirtuin activation, longevity, low insulin variability.
Some of the top fitness and health practitioners who are big on fasting are very low body fat, incredible shape.
Leading figures like Peter Attia, Tim Ferriss, Ben Greenfield, David Sinclair, Kevin Rose to name a few, all pro fasting, all in top shape/low body fat.
> and you become very injury prone
No, you become temporarily weaker, and that's only if you're fasting multiple days. It's recommended you work out during fasts... your body remains anabolic to muscle (barring other variables like elevated stress).
In spite of jamming as much junk food down my throat as I possibly could, I struggled to maintain weight on the Appalachian trail. You can definitely outrun a bad diet. (Not that it's a healthy way to live either.)
Gary Taubes book “Why we get fat,” is a great read on this subject.
But, yknow, HYOH
I have lost weight like that before, but can't maintain a 2 hour a day exercise routine.
I imagine you can't stay on the Appalachian trail forever.
So eventually a bad diet will lap us.
> According to the doctor it's because we're not supposed to keep a full schedule while fasting.
That's a standard answer that likely does not draw on his medical knowledge. People pass out even when not fasting (women more so than man, something to do with vagus nerve IIRC), and thousands of people do long wet fasts while keeping a full schedule with no ill effects.
Highly active is something you can be when you're at or approaching a healthy weight; the causality is IMO almost backwards from what you've described.
My wife and I are long distance hikers. That means carrying 10-15kg up and down mountains for 10-14 hours per day every day for 3-6 months.
It also means literally counting every calorie--because you have to plan it in week-long intervals and also optimize it for minimal weight and sufficient nutrients.
Sounds like a perfect recipe for weight loss right? Enter 'hiker hunger.'
Appetite is completely elastic. Your ability to perform depends on your brain's ability to produce happy endorphins and satisfaction signals etc.
That's where intermittent fasting is crucial. You exercise your body's regulatory functions. It's not just some belief or willpower or placebo I mean: at a chemical level you transform the function of your neurochemistry to improve your metabolic process.
Would you be able to use IF during a thru hike? I suspect that the answer is no. The weight gain problem for distance hikers is after the hike is finished and we reduce activity significantly. I've solved that by training for distance races when I'm not hiking.
Zach Bitter, the current 100 mile record holder, put it in a way that makes a lot of sense to me[0]. For a mere mortal, fasting for 6 hours puts you in the hole for about 700 kcal. A world class athlete like him is at more like a 2000+ kcal deficit. It's impossible to catch up once you get that far behind, and you end up losing weight and injuring yourself. I only burn about 800 kcal during training on an easy day, but I still find it nearly impossible to catch up if I miss a meal. I'm already eating 5x a day. It's hard to cram 5 full meals into a few hours.
[0]: https://zachbitter.com/blog/2014/04/06/intermittent_fasting_...
And weight gain is not contained to "after the trail"
And weight loss is not guaranteed.
It's great that you've found something that works for you. Like I said, it works for me too.
Bodies are different though.
"I've hacked around this problem" != "This problem is illusory"
Are you talking of this kind of thing, low body fat makes even this difficult, or are you talking of multi-day fasting?
Although there are other benefits to IF, the weight loss is principally from calories in, calories out, because it’s much harder to cram an excess of calories into a small time window unless you purposefully eat beyond satiation.
Is it? Study [1] claims "Mice fed an FS [fat and sugar] diet ad libitum (FSA) consumed the same amount of calories as mice fed within a 9 hr window of the dark phase (FST) [fat and sugar, time restricted] (Figure S2A, i), yet the FST [time restricted] mice gained less body weight"
and then "to investigate the therapeutic potential of TRF [Time Restricted Feeding], we tested whether TRF could reverse or arrest body weight gain [..] Within a few days the mice were habituated to the new feeding paradigm and continued to consume equivalent calories (Figure S2A, iv). The 13:12 FAT mice showed a modest drop in body weight"
[1] https://www.cell.com/cell-metabolism/fulltext/S1550-4131(14)...
From related work of https://www.salk.edu/scientist/satchidananda-panda/
I think "it has to be calories in/calories out because it's just common sense" is not nuanced enough for biological systems.
Fasting, to me, begins when all previous meals are digested
I successfully lost 50 lbs a few years ago doing keto and brought myself to exactly the middle of normal BMI.
While I was losing the weight, keto was easy -- I always had energy (more than ever before), felt great, wasn't getting sick.
But once I hit my target weight... all of a sudden keto became miserable. I had brain fog all the time, except for about the window of 2-4 hrs after each meal when my digestion seemed to peak. I started getting colds all the time.
Once I switched back to eating carbs, I felt great.
My theory is that your body burns fat proportionally to the amount of fat you have... and that it's fine to fuel yourself until you just don't have enough fat anymore to keep it going to even things out between meals.
I was pretty bummed actually to discover that keto doesn't work for me anymore, when I'm already at a healthy weight. I just loved the constant energy. But for however my body's built, it's just not an option for me anymore.
https://greatist.com/live/autophagy-fasting-exercise#definit...
I've fasted for up to 5 days before, and I felt just fine - especially on days 4 and 5, I actually feel like I have more mental clarity and drive than usual.
I guess this is always my question of anyone who has a positive experience with fasts. Personally, I have been at the mid-upper range of healthy bf%/weight for years and exercise frequently (running 30+ minutes 7 days a week for a few years, cycling 60+ minutes 2-3 a week this year) and find much shorter fasts (say, 20h) excruciating and completely draining mentally and physically. And I'm not at 7% body fat like that other guy. Lowest I got was maybe 14% while I was running daily; while I'm up to 18%ish now, fasting hasn't gotten any easier.
(Even if I skipped exercising, just the mental effects made my mood significantly worse by the end of the day, which makes it harder to work effectively in a collaborative environment.)
What's your non-fasting diet like? Fasting is the quickest way to get into ketosis. If you're used to eating a carb-heavy diet, the switch into ketosis can be brutal. So if you either ease off carbs leading up to the fast, or just all the time, it'll be easier.
The other thing is electrolytes. Your body doesn't store them, so you (IMO) have to supplement. If you start to feel like crap, have 1tsp of salt in about 1L of water and see if it fixes it. I also supplement with magnesium and occasionally potassium.
I'm sure Dorsey isn't the only high profile/ functioning CEO who does multi day fasts each week.
"Not only are we deeply wired to function for long periods of time without food"
So the body doesn't collapse after x number of hours without fuel. Your body also has the ability to generate its own heat when it's cold. Does that mean that it's desirable or ideal that we deliberately use these abilities? Does it mean that there is no harm or risk in doing so? I'm not saying that there is or isn't; I don't know.
"but when you haven't eaten in a while your mind becomes focused and alert"
This is sort of like the focus that you get when you're being chased by a wild animal or falling out of a tree. I don't know that seeking focus from sources like this is a great idea, but YMMV.
"since your body thinks it needs to find or hunt food."
So maybe your body is telling you that fasting isn't such a good idea?
"I'm sure Dorsey isn't the only high profile/ functioning CEO who does multi day fasts each week."
I don't do multi-day fasts and I've lived for years longer than Dorsey.
The evolutionary angle isn't the reason why I believe fasting is a good idea - it's just a rebuttle to "there's no way you function well while fasting"... of course you can, it was likely the MO for millions of years of modern human evolution (or 100+ M years for mammals). It's as natural to fast as it is to fornicate.
Rather, my reasons for fasting come from the scientific literature, centered around autophagy, insulin control, sirtuin activation, visceral (organ) fat depletion, and troves of clear lab test results of benefits (albeit most on non human mammals).
Based on many comments here I think folks just haven't caught up with the longevity research of the last 3-4 years.