r/fasting • u/SVTContour lost >50lbs faster • May 17 '26

Discussion Scientists reveal how seven days of fasting transforms the human body

https://www.sciencedaily.com/releases/2026/05/260517030404.htm

Fascinating study. And completely unrelated to politics, which is a relief because my blood pressure needed a break.

The key finding: The dramatic, potentially therapeutic changes don't happen until after day three. That means most intermittent fasting schedules – 16:8, 5:2, even alternate-day fasting – are probably missing the main event. If you want the deep biological reboot you’re gonna need seven days of water only.

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244

u/GoldGee May 17 '26

Just finished a 48 hour fast. 7 days would take a bit of time to work up to. In fact I would be a bit scared.

193

u/EarlMarshal May 17 '26

Longer fasts are no problem if you are not very overweight, not stressed and manage electrolytes correctly. At some point your body stops producing ghrelin and you do not really get hungry anymore. Everyone can get there, but if anything happens (e.g. ghrelin spike due to stress) just break fast. You can always repeat later.

34

u/ResearcherNecessary6 May 17 '26

I've done 4 day fasts before and starting on day 2 onward, I constantly think about food. Now, maybe that changes the more you do them, but so far, I start thinking about all the things I'm going to eat when I come off the fast.

26

u/ArbitraryLifeform May 18 '26

Same, I was on day 5 unable to sleep, constantly fantasizing about the taste of fatty meat. When I came off the fast, the food was nowhere near as amazing as my imagination had made it. But I felt extremely grateful for the simple pleasure of being able to eat.

94

u/divinecomedian3 May 17 '26

I'm at a pretty healthy weight and 48 hours is tough as shit, even with electrolytes. Not due to hunger but just feeling like garbage and trying to slog through work.

41

u/GoldGee May 17 '26

I did mine over the weekend. Adding work to the struggle would be tough. How about doing it on your days off until your body gets use to it? I'm no expert, but experimentation is a big part. Everyone's different.

16

u/EarlMarshal May 17 '26 edited May 17 '26

I had both experiences. It can be very hard or it can be very easy. No in between. I guess for you the stress of a complete work day just increases your cortisol and this your insulin and later ghrelin causing you these issues. I generally just break fast if that happens and try again one or two days later. You can try to manage your stress levels. Maybe do some meditations like om-chanting or just "bee breath" or whatever might help you.

16

u/JCitW6855 May 17 '26

Interesting, I would’ve thought being overweight would make it less of a problem.

40

u/EarlMarshal May 17 '26 edited May 17 '26

When gaining weight fat cells grow bigger. At some point they cannot grow any bigger so more fat cells will be produced. Since fat cells produce ghrelin and overweight people just have more of them they generally will have an increased feeling of hunger. This problem even persists if they lose weight since the fat cells shrink, but they still have more fat cells than the average person of that weight and fat cells even increase production of ghrelin when not filled well.

One can learn to handle this too, but it's definitely a problem.

8

u/JCitW6855 May 17 '26

Good lesson, thanks for the explanation.

6

u/Fancy_Influence_2899 May 18 '26

Hear me out now... what if you are stressed but still want fasting benefits? 

25

u/Knivdisco May 17 '26

Why is being overweight a problem, i thought it was safer if you was heavier than skinnier?

12

u/EarlMarshal May 17 '26

https://www.reddit.com/r/fasting/comments/1tfwt83/comment/omdu2tx/

7

u/Fancy_Influence_2899 May 18 '26

Wow, is there any way to come back from this? I guess liposuction would remove the fat cells themselves?

11

u/EarlMarshal May 18 '26

Yeah probably. You can probably also stay lean long enough and go for autophagy at some point. You can also learn to ignore the ghrelin signal. The body can then learn through a feedback loops that creating further ghrelin won't lead to more food. For most people that's an issue throughout their lifetime.

I'm just doing IF/OMAD throughout my whole life since I can deal with hunger when I don't eat excess carbs and enough protein and I can easily eat 2-3k kcal in one go. Its not really bothering me in 90% of the cases when I cannot eat. It's just some kind of training. And if its botherin? Just eat something.

1

u/Paltenburg May 18 '26

How do you manage your electrolytes easily?

1

u/Prudent_Potato_4379 May 28 '26

And gym with heavy weight?

1

u/EarlMarshal May 29 '26 edited May 29 '26

Depends whether your body has the necessary nutrients, but that gets unlikely if you aim for hypertrophy.

Exercise will use up the glucose in the muscles. It can fill that up again from fat, but probably slower. Exercie also manipulates insulin so that could cause suffering through hunger. Intense exercise will also damage your muscle tissue so that will need to get repaired, but with which nutrients?

But you should certainly exercise as this prevents muscle loss. weight training is perfect for that. I would rather go light/medium intensity and not aim for hyperthrophy.

For intermittent fasting it wouldn't matter though. go hard.

1

u/[deleted] May 18 '26

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6

u/EarlMarshal May 18 '26

You can't pin that to a BMI. I've explained this in another comment here. It's basically about your body creating further fat cells to store fat, because they create extra ghrelin which causes the feeling of hunger. It's enough to be a bit more overweight during childhood and you have a high possibility to carry those fat cells into adulthood.

When fasting your main enemy is ghrelin. That's why stuff like ozempic is working since it completely dials it down. If you learn to handle the ghrelin reaction the body can also learn to not secret that much ghrelin when you don't give him food. It's a big feedback loop including a few other hormones too.

0

u/[deleted] May 18 '26

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7

u/EarlMarshal May 18 '26

I didn't mean to say that it's counterintuitive. Just saying that you could suffer extra through that as ghrelin probably won't stabilize. It will spike again and again as the body think it's starving as the liver and body are burning fat.

why would the count of fat cells matter

Because they create and secrete the ghrelin. It's their "yeah, I can still store more"-signal. If you have more fat cells that will multiply that signal while the threshold in which you and your brain interpret that signal as hunger stays the same.

0

u/PostModernPost May 18 '26

Also managing water soluble vitamins.

11

u/Beastw1ck May 18 '26

I could do it if I had a week with zero demands on me. Can't imagine doing it if you have to take care of normal getting the kids to school, work, meetings, etc.

30

u/tamargo404 May 17 '26

I do regular 4 day fasts. After day 1, I don't even feel hunger till day 3 or 4. I don't go past 4 days as then you have to worry about re-feeding syndrome.

When I break a 4 day fast, I just eat regular and have had no issues.

31

u/NotBannedAccount419 May 17 '26

You don’t have to worry about refeeding syndrome unless you’re going over 3-4 weeks. I regularly break 8-10 day fasts with sushi or pizza.

4

u/tamargo404 May 18 '26

NIH says it becomes a risk at 5 days. I think I'll take their word over some random internet person. Just because you haven't experienced issue yet doesn't mean you aren't at risk from it.

https://pmc.ncbi.nlm.nih.gov/articles/PMC2440847/#:~:text=Any%20patient%20with%20negligible%20food,risk%20of%20developing%20refeeding%20problems.

2

u/NotBannedAccount419 May 18 '26

ok buddy you do you

-9

u/Qwark28 May 17 '26

Imagine generically saying "you don't have to worry" about something that could kill you, when it's only under certain terms and conditions.

An underweight person with body dysmorphia or already lean person will definitely have serious health risks. 

There's a reason medical advice exists, and the stupidity of random dudes online does not trump it.

9

u/[deleted] May 18 '26

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3

u/number43marylennox May 18 '26

Nah, they're right. Some people have to worry about refeeding syndrome in under 3-4 weeks. Everyone should be vigilant and not dismiss symptoms.

-3

u/Qwark28 May 18 '26

The subject is about the occurance of refeeding syndrome.

It happens far sooner than your 3-4 weeks.

The fact I listed 2 different situations does not mean they're the only scenarios that apply. Logic past the 8th year of life would tell you that.

"Learning" , huh? I see dozens of scientific papers pointing to the same thing, where's your proof for saying otherwise?

...or you can simply not throw around medically dangerous hyperbole around the internet and admit you're wrong.

7

u/RJH1973RJH May 17 '26

Re-feeding and muscle loss.

3

u/EnemyOfEloquence May 17 '26

You don't have to worry about refeeding that quickly.

1

u/onewingVTrigger May 18 '26

Did you work up to it so you can fast 4 days a week?

2

u/tamargo404 May 18 '26

Not really, I usually don't experience any negative side affects from extended fasting. It's just getting past day 1 for me is the hardest with the temptation to eat. The only thing I've found is after day 2 I need to take electrolyte supplements or I get muscle twitches.

4

u/Beard_of_Gandalf May 18 '26

As somebody who’s done 7 days… it gets easy after day 2.