Can anyone point me to the research/notes which say that 48hr fasting is much harder than 24hr or > 48hr

(Preet) #1

I heard Richard and Richard talking about it on an earlier podcast but I cannot seem find it again.

thanks Team

(Bob M) #2

That would be interesting to see. I know Dr. Fung has said the second day of a longer fast is usually the worst. I have found this to be mainly true, though I also remember getting ravenous Thursday night, 4 days into a fast. I made it to the next day, but it was tough.

#3

People are metabolically different, I doubt any study could look into that accurately. Thereā€™s way too many differences to account for. My first fast was 3-4 days and i never felt it. Others want to rip their face off by the time they hit 24hrs, fat adapted or not.

(Doug) #4

Iā€™ve never seen formal research on it, Preet. But from reading a lot - like many hundreds if not thousands of accounts of fasting - I donā€™t think 48 hours itself presents any special necessary problems, overall, versus 1 day or just ā€œmore than 48 hours,ā€ but perhaps the 3rd day, 4th day, etc., might be easier, on average.

A substantial number of people feel rough around 18 hours, and I think this makes sense - at this point your stomach is empty, and the small intestine is too, or close to it. The ā€˜post-absorptive phaseā€™ (as Dr. Fung calls it, anyway) is underway, and the blood sugar level is starting to decline. Itā€™s enough of a thing that many people time it so that that period is while theyā€™re asleep - like if somebody is on a ā€˜normalā€™ daylight schedule then they eat in the morning, go to bed ~ 14 or 15 hours later, and when they wake up itā€™s been 21+ hoursā€¦

The second day is often ā€œharderā€ than the first, probably because then the digestive system really is pretty empty, as far as contributing energy. Weā€™re into burning glycogen then, maybe even going into fat-burning.

Coming from a ketogenic diet would usually alter this (all other things being equal). It should be a smoother-transition to burning fat, and the body would likely feel less deprivation.

During Day 3, I think whatever glycogen depletion is going to occur has happened, or is mostly finishing up. Gotta really be running on fat somewhere in there, so for better or worse it will be more steady-state afterwards. Personally, I do think that intentionally stopping a fast at 2 days will usually be counter-productive, i.e. itā€™s not like it usually gets harder afterwards, thus if anything Iā€™d say it takes more ā€œeffort per dayā€ to get through the first 2 days, so why not keep going? Of course there may be other considerations, too.

Individual variation and experience with fasting also make a huge difference. Doing several longer fasts tends to make shorter ones comparatively really easy, especially compared to the first time one goes for 48 hours, or whatever length one chooses. Iā€™ve done 12 days, 10 days, and about 30 fasts of 3 to 6 days. The first 2 days are no problem at allā€¦

(Bob M) #5

12 and 10 days ā€“ Thatā€™s impressive. My max was 5.5 days, and I started getting dizzy when standing, so I quit. Weekends are the toughest for me, so Iā€™ve done a lot of 4.5-5 day fasts, mainly 4.5 days, since I could eat Sunday evening and make it to Friday sometime, and eat then.

For me, over time, fasting has gotten harder, not easier. A few years ago, a 4.5 day fast was nothing, and I was doing 36 hour fasts all the time, and exercising at about 32 hours. This year, Iā€™ve only done one 4.5 day fast, and not many 36 hour fasts. Itā€™s harder now, though the pandemic hasnā€™t helped (kids home every night).

(Pam ) #6

Everyone is different, for sure. I find the first 24 hours the worst, then I am good. Day 2 and day 7 feel the same for me.

#7

Surely itā€™s not true for everyoneā€¦ But it makes sense to me. The first day should be easy as we donā€™t get hungry yet? :smiley: (Not like I am good at waiting until hungerā€¦ I suck at it. But if I am determined, I can do it.) At least people with a naturally small eating window. Not eating for nearly a day is normal, happens a lot so itā€™s no big deal to do it or a bit more hours when we are determined to fast. Then we miss a meal and things may get harder (with a usually bigger eating window it should happen earlier than 24 hours). But later I seem to get disconnected from eating - but I have very little experience with that. I usually miss my meals, at least mentally and eat. It was ages ago when I went over 48 hours despite I wasnā€™t always hungry at that point. Sometimes real hunger just doesnā€™t come until the 5th day (okay, that was once and no hunger for 45-48 hours happened multiple times and I broke my fast then with or without hunger).

If my last meal is right (size, timing) and I sleep when I should, the first 20-26 hours are nothing (longer if I ate earlier last. my hunger tends to follow the actual time, not the hours passed from my last meal). If the meal is problematic, the first hours are the hardest (well no, I just eat then) and if I am not asleep when I reach the 8th-12th hour (it shifted with time), thatā€™s usually a problem too but I am almost always asleep then and after a good sleep, I am very satiated for long againā€¦ At least in the beginning but then eating becomes an abstract conceptā€¦

(Doug) #8

:slightly_smiling_face: Iā€™d say that is a pretty good thing. Is this always true, Pam? Is one fast as easy as past fasts, or the next one?

There is also a very possible 363 kilgram gorilla in the room, so to speakā€¦ The psychological component of fasting is huge, for many of us. Iā€™m not saying that physical sensations and effects wonā€™t be present and real - and the leaner we are, the more quickly these will assert themselves, in general.

But as one gets away from the really low body fat percentages for their sex, I think the mental part of the game gets big and usually overpowers the physical stuff, especially after one is used to fasting. Iā€™ve yet to have ended a fast because I physically felt like I had to. Itā€™s always because of a social meal I donā€™t want to miss, because I was bored, etc.

I donā€™t mean to generalize for everybody - as individuals we certainly can differ, even if we have the same body fat percentage, for example. And even for a given individual, thereā€™s usually substantial variation among fasts, i.e. you never know how it will go. But the emotional/mental thing shouldnā€™t be underestimated.

(Pam ) #9

OldDougā€¦Iā€™m not saying they are all easy. LOL. But for me, the absolute worst day of the fast is always the first one.

(Michael - When reality fails to meet expectations, the problem is not reality.) #10

When I started keto I did so with a 96-hour fast (4 days). On day 2 (24-48 hours) I felt most severely hungry. I call this hunger ā€˜carb hungerā€™ and describe it as like the flesh eating plant from the movie Little Shop of Horrors demanding to be fed constantly. This hunger was most pronounced the morning of day 2 and declined slowly/steadily throughout the day. From the morning of day 3 the severe hunger of day 2 was replaced with a much more subdued/subtle hunger. I call this hunger ā€˜keto hungerā€™ and describe it as the company accountant announcing at the monthly board meeting that outgo exceeded income during the previous month and the difference had to be made up from current accounts.

Please note, this experience was going from SAD to keto. I havenā€™t done any multi-day fasting while in ketosis. Now, I only do 10/14, 12/12 or 14/10 IF from supper to breakfast. Last night to this morning, for instance, I did a 14/10 IF. Felt zero hunger.

Edit: corrected my IF numbers.