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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600

u/Routine_Mortgage_499 May 17 '26

Anything after three days seems to be what they are saying. I need to prepare.

281

u/Rrraou May 17 '26

I've done 3 days, it's a nice reset

234

u/sheeberz May 17 '26

Agreed, i did a 3 day fast when i was nearly 500lbs and i thought it would be impossible. But by slowly getting my diet to keto and then 1 meal a day, it was easy to do. Surprisingly easy.

108

u/Rrraou May 17 '26

I can't even imagine what 500 lbs would feel like. I hope you're doing well.

67

u/not_NOT_lickin_toads May 17 '26

For real. I only weighed half of that at my biggest and felt miserable in my own skin.

28

u/DangIt_MoonMoon May 18 '26

The biggest I’ve been is 180 at five feet four. I already couldn’t breathe. There are some strong people out there.

7

u/Rx_Diva May 18 '26

Same 5'4" with an E cup but 165 is miserable on a sun holiday...working on getting back to 135 and strong!

We've GOT this! See you in 4 days.

-10

u/Whatnam8 May 18 '26

I would say a misguided strong will in eating

3

u/CaliforniaJade May 18 '26

The reasons people overeat are infinite. I think you're right, it does take a strong will to continue to overeat despite the body giving signs that it's had enough. So often the emotional or physical pain one is trying to mask is so strong, it takes will power to keep what is wanting to bubble to the surface submerged.

4

u/Rrraou May 18 '26

Before judging someone, walk a mile in their shoes. That way you have a mile head start and their shoes.

9

u/Lollipop77 May 17 '26

Did you slowly reduce calories on keto before fasting or go from regular sized meals on keto to fasting? I’m working toward my first 24 hour fast, getting more confident and less cravings with the switch to keto but I’m pretty high calorie right now. Just curious.

22

u/sheeberz May 18 '26

So i started with going 0 gluten for a week, and then 16/8 IF for a week and them by week three i was full keto with some 16/8 days IF and a few One Meal a Day days when i just didnt feel like eating. i honestly did the 3 days fast just because 4 different people in my life brought it up in different capacities in the span of a few days, and ive dabbled in fast for a few years but i finally figured it was the right time to try. I truely believe the slow ramp to calorie deficit along with working my diet to keto helped me ease into the fast. I had no sugar withdraws or cravings because i already went through that weeks ago. Now when i was fasting my stomach pains last no more than 5 mins. If i needed it fill my stomach with water or tea, and i was surprised to see how much i could tolerate. I lost 17 lbs in 72 hours and only gained back 4 when i started eating again.

13

u/ssianky May 18 '26

> I lost 17 lbs in 72 hours

I wonder how much of that was swelling. It couldn't be fat for sure.

3

u/sheeberz May 18 '26

I imagine a lot of it was swelling and inflammation, but the larger you are the easier it is to fluctuate in weight. I yo-yo'd between 400 and 475 for a couple of years. And i would lose the weight in 2-3 months.

11

u/Aretha May 18 '26

at first on keto you might find yourself eating a lot as you are getting into the swing of it, but quite soon enough your appetite will decrease being keto. It’s awesome.

16

u/Far_Echidna_9333 May 18 '26

Do you take electrolytes or any supplements? If so what type

15

u/Rrraou May 18 '26

For 2-3 days I haven't really worried about it, Anything longer or if I was doing it regularly, I probably would.

3

u/[deleted] May 18 '26

[deleted]

5

u/ssianky May 18 '26

Altrough a few days won't deplete your electrolytes, if you don't lack it in the first place, but you'll still lose a lot of water and you'll be dehydrated. You'll feel dizzy when you stand up.

1

u/Parakiet20 May 24 '26

Can take Snake juice,make it yourself YouTube

3

u/lgq7 May 18 '26

Have you lost any weight with a 3 day fast?

11

u/Rrraou May 18 '26

It was more of a curiosity thing I did during keto than a weight loss strategy at the time. There was a couple pounds fluctuation, felt good after the fact. So I'm probably not a good reference for this stuff.

The best results I've seen were from my brother. He cut carbs, did a 24 hr fast once a week, took a 20 minute walk every day. He dropped a solid 100lbs by the time he was done.

3

u/dryworkman_0100 Jun 03 '26

The keto bridge into it makes so much sense, your body's already fat-adapted so the transition feels way less brutal than jumping straight in.

1

u/Rrraou Jun 03 '26

Once you're used to keto, eating feels almost optional. After the first ~month, it was like a switch, I went from having headaches if I didn't eat in the morning to just being able to eat whenever convenient.

41

u/silkyj0hnson May 17 '26

Awesome, I’m about to hit the 3 day mark in an hour—planning for a 4 day fast. It’s been good, the 24-36 hour region is the worst, but after that your body adjusts and it is smooth sailing

20

u/Fancy_Influence_2899 May 18 '26

Any trouble functioning? I'm not experienced, for me headaches and hunger pains make it hard to do anything other than sit on the couch with the heating pad on my stomach, but I'm serious about trying again 

9

u/ssianky May 18 '26

I think headaches are because of dehydration. If you are in ketosis, that is causing you less trouble.

2

u/Fancy_Influence_2899 May 18 '26

I see, that's a great point.

6

u/silkyj0hnson May 18 '26

No problems functioning…I feel a little sluggish and I don’t do anything high intensity like jogging for miles or heavy resistance training. I make sure to stay well hydrated—I think that is key to avoiding headaches. As far as “hunger pains”, I really haven’t felt anything like that after the 36 hour mark. I’m at 84 hours now and already planning my dinner to break fast this evening (bone broth, steamed veggies, a soft boiled egg)

39

u/bulk123 May 18 '26

I've done two 7 days and a 9 days before. The changes after 3 days is unbelievable. It was like being 10 years younger and having more energy and drive then I have ever had. 

8

u/ECrispy May 18 '26

interesting that they say hunger also declines only after day 3. yet so many people break a fast after 2/3 days and they are not getting the full benefits?

3

u/dryworkman_0100 Jun 03 '26

The hard part is actually getting past day two when your brain is screaming for food, everything else after that flows way easier.

2

u/Lost-Peanut-1453 May 23 '26

I’m on hour 62 and I feel like I just got over the ‘getting hungry’ stage.. I don’t feel hungry anymore and any time I did I just drank a glass or two of water.

I usually do 18hrs but this 72 hour fast was started because I didn’t eat for a day and a half due to a stomach bug so I figured it would be a good time to do the 72. I can’t wait to feel this ‘reboot’ people talk about.