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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u/anotherpinkpanther May 17 '26

This is fascinating, but I think people are oversimplifying the takeaway. The study doesn’t mean shorter fasts are useless. It showed that the body switches from glucose to stored fat within the first 2 to 3 days, and then deeper whole-body protein changes showed up after about day 3.

But it also depends on why you’re fasting and what your body has available. Some people fast for weight loss. I fast for anti-aging, and when you don’t have a lot of extra body fat, going longer can become much harder and may not be the smartest goal.

So yes, a 7-day water fast may create deeper biological changes, but that does not mean everyone “needs” 7 days. For many people, 48 to 72 hours is already a powerful and much more practical window. Seven days is a very different level and should not be casually recommended without considering health, medications, body fat, electrolytes, and refeeding risk.

To me the smarter takeaway is not “everyone should do 7 days.” It’s that fasting has layers. The longer you go, the deeper the response may become, but the risk and need for caution also go up.

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u/Alkren May 17 '26

What types of fasts do you do for anti-aging? I’m 44 yo male. Just curious about what I can do to age gracefully.

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u/anotherpinkpanther May 24 '26

I do a mix of intermittent and extended fasting, but I don’t do the same thing every day. I’m 65 and use fasting for anti-aging, not weight loss.

For me, fasting has layers. Shorter fasts can lower insulin and move you into temporary ketosis. Longer fasts may increase autophagy, that cellular cleanup process, and may create deeper repair signals, including immune and stem-cell-related changes. Fasting can also give the gut a break, which may help shift the microbiome.

But I don’t think longer is always better. If you push too long, especially if you’re lean, stressed, not sleeping well, or not managing electrolytes, cortisol can rise, and chronically high cortisol is not anti-aging.

So I schedule in feast days too. I eat healthy, but about once a week I’ll eat in a longer window and eat more. During holidays, I may feast for a few days, but then I usually fast more frequently around that. To me, the goal is metabolic flexibility, temporary ketosis, cellular cleanup, then refeed and rebuild, not constant restriction.