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Comment by d--b | Hacker News Reader

All the muslim world does 4-week intermittent fasting every year. That'd make it easy to test the asumption of the paper on a large scale population

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They do, but my colleagues tell me that the food they eat when they break their fast is often heavier than usual, and they might eat more as well. More than one is gaining weight during Ramadan :)

It may be wise to test your colleagues assumption while we're at it as well :)

A very important difference is that you can't drink water during a Ramadan fast. Regardless of what you're doing with your food, deliberately dehydrating yourself is pretty much never justified.

When I first heard of abstaining from water while fasting I also had a strong emotional reaction to the idea.

After realizing that water is a byproduct of catabolism, I'm willing to entertain the idea that it is beneficial.

It's not an emotional reaction - we have plenty of evidence about the negative impact of dehydration and no substantial evidence in favor of it.

> After realizing that water is a byproduct of catabolism, I'm willing to entertain the idea that it is beneficial.

The two parts of this sentence aren't connected by logic.

I'll clarify the sentence.

The body produces water as a byproduct of ATP (energy) metabolism. During a fast, fat and other tissues are broken down by catabolic reactions to accomplish this. Knowing this, I am willing to entertain the idea that abstaining from water for a period of time can be beneficial, or perhaps I should say at least not harmful, because there are mechanisms in the body that synthesize water. Obviously, a sufficiently long period of time without water would be harmful.

I haven't done the math to figure out how much water this is, and so I do not know how sufficient it is to keep minimally hydrated during a water-fast. I'm just saying that the thought of abstaining from water during a fast isn't necessarily as dangerous as it sounds, because your body can and does produce it's own water as a by-product of energy metabolism.

> I haven't done the math to figure out how much water this is

From https://en.wikipedia.org/wiki/Metabolic_water

> Humans obtain only about 8-10% of their water needs through metabolic water production

But the article states no eating and no drinking as fasting so it also involves deliberate dehydrating.

Yes, because they selected subjects who were observing Ramadan and that makes their study easier to carry out. My point is that the dehydration is counterproductive.

Most articles and videos on intermittent fasting say that drinking water is fine. Artificialy sweetened drinks are also a no go.

Exactly. Maybe I wasn't clear in my comment above. My point is that most resources on intermittent fasting allow (and actually encourage) drinking a lot of water, and rightfully so. At the same time a lot of the research is done on subjects who observe Ramadan fasting and do not drink water. This difference has to influence the results in some way.

"never justified"

A religious obligation won't count as justification?

I think the logical interpretation of GP is that it's never justified from the perspective of physical health. Whether religious obligations outweigh ones health is a completely personal decision that no outsider gets any say in.

1. Some folks cheat. 2. Some, who you would think are otherwise healthy, cannot fast (I have a friend that found out he cannot fast. He was instead hospitalized). 3. The severity of the fast depends on the time of year the fast falls and where in the world you are. Right now, it is certainly worse in Norway (where the days very long in June) than it is in the southern hemisphere, where the days have their winter lengths.

The last two can be somewhat accounted for (and already are: Folks that can't fast are exempt and special rules for places that get midnight sun). We can't really control for the first one, especially with real cultural taboo against breaking the fast during the day.

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